阅读说明：本技术 钛合金的微观结构改进 (Microstructure improvement of titanium alloy ) 是由 P·H·谢菲尔德 J·A·小格罗霍斯基 于 2020-03-15 设计创作，主要内容包括：公开了一种用于改进先前通过选择性熔化工艺制造的基础钛合金制品的物理特性的方法。该方法包括通过热氢工艺向基础钛合金制品引入氢,所产生的钛合金制品表现出各向同性的细化晶粒的等轴微观结构。热氢工艺可包括将氢引入基础钛合金制品,以降低β转变温度,将基础钛合金制品加热至高于降低的β转变温度,以形成氢化β,降低基础钛合金制品的温度以影响共析转变,并通过真空加热使基础钛合金制品脱氢。基础钛合金制品可以具有提高的氧含量和/或氢可以以0.4重量％或更高的比例引入。(A method for improving the physical properties of a base titanium alloy article previously manufactured by a selective melting process is disclosed. The method includes introducing hydrogen to a base titanium alloy article via a hot hydrogen process, the resulting titanium alloy article exhibiting an isotropic equiaxed microstructure of refined grains. The hot hydrogen process may include introducing hydrogen into the base titanium alloy article to reduce a beta transus temperature, heating the base titanium alloy article above the reduced beta transus temperature to form a hydrogenated beta, reducing a temperature of the base titanium alloy article to affect a eutectoid transformation, and dehydrogenating the base titanium alloy article by vacuum heating. The base titanium alloy article may have an increased oxygen content and/or hydrogen may be introduced at a rate of 0.4 wt% or more.)

1. A method for improving physical properties of a base titanium alloy article previously manufactured by a selective melting process, the method comprising:

hydrogen is introduced to the base titanium alloy article by a hot hydrogen process, and the resulting titanium alloy article exhibits an equiaxed microstructure of isotropic and refined grains.

2. The method of claim 1, wherein the base titanium alloy article exhibits more anisotropy and coarser grain quality than the resulting titanium article.

3. The method of any one of the preceding claims, wherein the resulting titanium alloy article exhibits an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 100 microns.

4. The method of any one of the preceding claims, wherein the resulting titanium alloy article exhibits an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 50 microns.

5. The method of any one of the preceding claims, wherein the resulting titanium alloy article exhibits an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 20 microns.

6. The method of any one of the preceding claims, wherein the resulting titanium alloy article exhibits an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 10 microns.

7. The method of any one of the preceding claims, wherein the step of introducing hydrogen by a thermal hydrogen process comprises:

introducing hydrogen into the base titanium alloy article to reduce the beta transus temperature;

heating the base titanium article above the reduced beta transus temperature to form a hydrogenated beta;

reducing the temperature of the base titanium alloy article to affect eutectoid transformation;

the base titanium alloy article is dehydrogenated by vacuum heating.

8. The method of any of the preceding claims, wherein the step of heating the base titanium article above the reduced beta transus temperature to form hydrogenated beta produces a temperature in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

9. The method of any of the preceding claims, wherein the step of dehydrogenating the base titanium alloy article by vacuum heating produces a temperature in a furnace having any of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

10. The method of any one of the preceding claims, where the step of introducing hydrogen introduces 0.4 wt.% hydrogen or more.

11. The method of any one of the preceding claims, where the step of introducing hydrogen introduces 0.5 wt.% hydrogen or more.

12. The method of any one of the preceding claims, wherein the step of introducing hydrogen is from 0.5 wt.% hydrogen to 1.5 wt.% hydrogen.

13. The method of any of the preceding claims, wherein the oxygen content of the base titanium alloy article is greater than any of 2000ppm, 2500ppm, 3000ppm, 3500ppm, and 4000 ppm.

14. The method of any one of the preceding claims, wherein the base titanium alloy article is a surgical implant.

15. The method according to any one of the preceding claims, wherein the base titanium alloy article is a hip stem.

16. The method of any one of the preceding claims, wherein the resulting titanium alloy article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

17. The method of any one of the preceding claims, wherein the base titanium alloy article is manufactured from a first entity and the step of introducing hydrogen by a thermal hydrogen process is performed from a second entity.

18. The method of any of the preceding claims, wherein the base titanium alloy article is manufactured in a first apparatus and the step of introducing hydrogen by a hot hydrogen process is performed in a separate apparatus remote from the first apparatus.

19. The method of any of the preceding claims, further comprising subjecting the base article or the resulting article to hot isostatic pressing.

20. The method of any of the preceding claims, further comprising subjecting the base article to hot isostatic pressing prior to the step of introducing hydrogen.

21. A method for processing a selectively melted titanium article, comprising:

introducing hydrogen into the article to reduce the beta transus temperature of the article;

heating the article above the reduced beta transus temperature to form hydrogenated beta;

reducing the temperature of the article below the eutectoid transition point; and

the article is dehydrogenated by vacuum heating to form a fabricated article.

22. The method of claim 21, wherein the step of heating the article above the reduced beta transus temperature to form a hydrogenated beta phase is performed in a furnace having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

23. The method of any one of claims 21 to 22, wherein the step of dehydrogenating the article by vacuum heating to form the fabricated article is performed in a furnace having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

24. The method of any of claims 21 to 23, wherein the grain size of the worked article is smaller than the grain size of the green article.

25. The method of any of claims 21 to 24, wherein the grain size of the fabricated article is less than 100 microns.

26. The method of any of claims 21 to 25, wherein the grain size of the fabricated article is less than 50 microns.

27. The method of any of claims 21 to 26, wherein the grain size of the fabricated article is less than 20 microns.

28. The method of any of claims 21 to 27, wherein the grain size of the fabricated article is less than 10 microns.

29. The method of any of claims 21 to 28, further comprising subjecting the article or the fabricated article to hot isostatic pressing.

30. The method of any of claims 21 to 29, further comprising subjecting the article to hot isostatic pressing prior to the step of introducing hydrogen.

31. The method of any one of claims 21 to 30, further comprising annealing the article prior to the step of introducing hydrogen.

32. The method of any one of claims 21 to 31, wherein the step of introducing hydrogen introduces 0.4 wt.% hydrogen or more.

33. The method of any one of claims 21-32, wherein the step of introducing hydrogen introduces 0.5 wt.% hydrogen or more.

34. The method of any one of claims 21 to 33, wherein the step of introducing hydrogen introduces 0.5 to 1.5 weight percent hydrogen.

35. The method of any one of claims 21 to 34, wherein in the step of heating the article above the reduced beta transus temperature, the article is heated to 10 ℃ to 75 ℃ above the reduced beta transus temperature to form a hydrogenated beta phase.

36. The method of any one of claims 21 to 35, wherein the temperature resulting from the step of heating the article above the reduced beta transus temperature to form a hydrogenated beta phase is maintained for 30 to 60 minutes.

37. The method of any one of claims 21 to 36, wherein the temperature resulting from the step of lowering the temperature of the article below the eutectoid transition point is maintained for 3 to 6 hours.

38. The method of any one of claims 21 to 37, wherein the step of dehydrogenating the article by vacuum heating to form the fabricated article is performed between 650 ℃ and 850 ℃ for 2 to 48 hours.

39. The method of any one of claims 21 to 38, wherein:

the step of introducing hydrogen introduces 0.5 to 1.5 weight percent hydrogen;

heating the article to 10 ℃ to 75 ℃ above the transition temperature in the step of heating the article above the reduced beta transition temperature to form a hydrogenated beta phase;

heating the article above the reduced beta transus temperature to form a hydrogenated beta phase at a temperature of from 30 to 60 minutes;

maintaining the temperature resulting from the step of lowering the temperature of the article below the eutectoid transition point for 3 to 6 hours; and the number of the first and second groups,

the step of dehydrogenating the article by vacuum heating to form the fabricated article is carried out between 650 ℃ and 850 ℃ for 2 to 48 hours.

40. The method of any one of claims 21 to 39, wherein the oxygen content of the article is greater than any one of 1300ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, or 4000 ppm.

41. The method of any one of claims 21 to 40, wherein the article is a surgical implant.

42. The method of any one of claims 21-41, wherein the article is a hip stem.

43. The method of any of claims 21 to 42, wherein the worked article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

44. A titanium alloy article comprising:

an oxygen content greater than 2000 ppm;

refining the equiaxed microstructure of the grains; and the number of the first and second groups,

grain size of less than 100 microns.

45. The titanium alloy article of claim 44, wherein said article comprises an isotropic microstructure.

46. The titanium alloy article of any one of claims 44 to 45, wherein the grain size is less than 50 microns.

47. The titanium alloy article of any one of claims 44 to 46, wherein the grain size is less than 20 microns.

48. The titanium alloy article of any one of claims 44 to 47, wherein the grain size is less than 10 microns.

49. The titanium alloy article of any one of claims 44 to 48, wherein an equiaxed microstructure of refined grains is a result of thermal hydrogen treatment.

50. The titanium alloy article of any one of claims 44 to 49, wherein the oxygen content is greater than 2500ppm, 3000ppm, 3500ppm, or 4000 ppm.

51. The titanium alloy article of any one of claims 44 to 50, wherein said article is a surgical implant.

52. The titanium alloy article of any one of claims 44 to 51, wherein the article of manufacture is a hip stem.

53. The titanium alloy article of any one of claims 44 to 52, wherein said article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

54. The titanium alloy article of any one of claims 44 to 53, wherein the article is a high strength titanium article.

55. A method for improving physical properties of a base titanium alloy article having an increased oxygen content, the method comprising:

introducing at least 0.4 wt.% hydrogen into a base titanium alloy article to reduce a beta transus temperature, heating the article above the reduced beta transus temperature to form a hydrogenated beta, reducing the temperature of the article to effect a eutectoid transformation, dehydrogenating the article by vacuum heating to form a resultant article;

the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 100 microns;

wherein the increased oxygen content is above 2000 ppm.

56. The method of claim 55, wherein the resulting article exhibits an isotropic microstructure.

57. The method of any one of claims 55 to 56, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

58. The method of any one of claims 55 to 57, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

59. The method of any one of claims 55 to 58, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

60. The method of any one of claims 55 to 59, wherein the step of heating the article above the reduced β transus temperature is performed in an oven having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

61. The method of any one of claims 55 to 60, wherein the step of dehydrogenating the article by vacuum heating is carried out in a furnace having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

62. The method of any one of claims 55 to 61, wherein the step of introducing hydrogen is at least 0.5 wt.% hydrogen.

63. The method of any of claims 55 to 62, wherein the step of introducing hydrogen is from 0.5 weight percent hydrogen to 1.5 weight percent hydrogen.

64. The method of claim 55, wherein:

the step of heating the article above the reduced beta transus temperature is performed in an oven having a temperature uniformity of either: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below;

the step of dehydrogenating the article by vacuum heating is carried out in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below; and the number of the first and second groups,

the step of introducing hydrogen is from 0.5 weight percent hydrogen to 1.5 weight percent hydrogen.

65. The method of any one of claims 55 to 64, wherein the increased oxygen content is greater than any one of 2500ppm, 3000ppm, 3500ppm, and 4000 ppm.

66. The method according to any one of claims 55 to 65, wherein the titanium alloy article is a surgical implant.

67. The method of any one of claims 55 to 66, wherein the titanium alloy article is a hip stem.

68. The method of any one of claims 55 to 67, wherein the titanium alloy article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

69. The method of any one of claims 55 to 68, wherein the titanium alloy article is a high strength titanium alloy article.

70. A method for improving physical properties of a titanium alloy article, the method comprising:

introducing at least 0.4 wt.% hydrogen to the titanium alloy article to reduce the beta transus temperature;

heating the article to a temperature above the reduced beta transus temperature to form hydrogenated beta, the heating being in a furnace having a temperature uniformity of +/-28 ℃ or less;

lowering the temperature of the article to effect eutectoid transformation;

dehydrogenating the article by vacuum heating to form a resulting article;

wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 100 microns.

71. The method of claim 70, wherein the step of introducing hydrogen to the titanium alloy article to reduce the beta transus temperature introduces at least 0.5 wt.% hydrogen.

72. The method of any one of claims 70-71, wherein the step of introducing hydrogen to the titanium alloy article to reduce the beta transus temperature introduces 0.5 wt.% hydrogen to 1.5 wt.% hydrogen.

73. The method of any one of claims 70 to 72, wherein the resulting article exhibits an isotropic microstructure.

74. The method of any one of claims 70 to 73, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

75. The method of any one of claims 70 to 74, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

76. The method of any one of claims 70 to 75, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

77. The method of any of claims 70-76, wherein the titanium alloy article has an oxygen content greater than 2000 ppm.

78. The method of any one of claims 70 to 77, wherein the oxygen content of the titanium alloy article is greater than 3000 ppm.

79. The method of any one of claims 70 to 78, wherein the step of heating the article above the reduced beta transus temperature to form hydrogenated beta is performed in a furnace having a temperature uniformity of any one of: +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

80. The method of any one of claims 70 to 79, wherein the step of dehydrogenating the article by vacuum heating is performed in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

81. The method of any one of claims 70-80, wherein the resulting article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

82. The method of any one of claims 70 to 81, wherein the article produced is a surgical implant.

83. The method of any one of claims 70-82, wherein the resulting article is a hip stem.

84. A method for improving physical properties of a titanium alloy article, the method comprising:

introducing at least 0.4 wt.% hydrogen to the titanium alloy article to reduce the beta transus temperature;

heating the article to a temperature above the reduced beta transus temperature to form hydrogenated beta;

lowering the temperature of the article to effect eutectoid transformation;

dehydrogenating the article by vacuum heating to form the resulting article, the vacuum heating being in a furnace having a temperature uniformity of +/-28 ℃ or less;

wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 100 microns.

85. The method of claim 84, wherein the step of introducing hydrogen to the titanium alloy article to reduce the beta transus temperature introduces at least 0.5 wt.% hydrogen.

86. The method of any one of claims 84 to 85, wherein the step of introducing hydrogen to the titanium alloy article to reduce the beta transus temperature introduces 0.5 wt.% hydrogen to 1.5 wt.% hydrogen.

87. The method of any one of claims 84 to 86, wherein the resulting article exhibits an isotropic microstructure.

88. A method according to any of claims 84 to 87, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

89. The method of any one of claims 84 to 88, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

90. The method of any one of claims 84 to 89, wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

91. The method of any one of claims 84 to 90, wherein the oxygen content of the titanium alloy article is greater than 2000 ppm.

92. The method of any one of claims 84 to 91, wherein the oxygen content of the titanium alloy article is greater than 3000 ppm.

93. The method of any one of claims 84 to 92, wherein the step of heating the article above the reduced β transus temperature to form hydrogenated β is performed in a furnace having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

94. The method of any one of claims 84 to 93, wherein the step of dehydrogenating the article by vacuum heating is performed in a furnace having a temperature uniformity of any one of: +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

95. The method of any one of claims 84 to 94, wherein the resulting article exhibits fatigue properties comparable to or better than a wrought material of the same titanium alloy.

96. The method according to any one of claims 84 to 95, wherein the produced article is a surgical implant.

97. The method of any one of claims 84-96, wherein the resulting article is a hip stem.

Technical Field

The present disclosure relates to techniques for improving the titanium microstructure of titanium articles. While these techniques may be used to improve titanium articles manufactured by a variety of techniques, the present disclosure is particularly concerned with homogenization of additively manufactured titanium articles. This includes homogenization to improve performance characteristics.

Background

It is well known that titanium additive manufacturing is itself a layer-by-layer manufacturing process, which is reflected in the macro and micro structure of the article manufactured by this method. In fact, the direction of the build is discernable through the build layer, and the microstructure has a columnar nature. Such highly oriented structures are produced in a selective melting additive manufacturing process by the sequential melting and solidification of each individual layer and the adjacent relationship of each layer to the next layer subjected to similar thermal cycling. Because the article is built in one direction, the microstructure of the article necessarily differs when viewed "against the build direction" and "along the build direction". Furthermore, the microstructure is highly directional. This is referred to herein as "anisotropy".

The difference in microstructure results in a difference in mechanical properties such that a single material, when tested in one direction, will exhibit better properties than in the other direction, e.g. "against build" versus "along build".

This is generally considered disadvantageous because these differences must be taken into account when designing and applying the manufactured article of additive manufacturing. This may also lead to a reduction in the valuation of the material, limiting performance to the "weakest" direction. Differences in microstructure can also lead to manufacturing inefficiencies as it dictates how the product must be oriented during the build process, which can affect the ability or efficiency of the additive manufacturing operation.

Disclosure of Invention

All manifestations of titanium metal additive manufacturing techniques, which involve melting events to consolidate (consolidate) materials, encounter difficulties caused by directional build-up and anisotropy. This includes processes that use a powder bed fusion process in which an article is constructed by selective melting of successive layers of titanium powder. The energy source for powder bed fusion is typically a laser or electron beam. In general, other additive technologies can be categorized as directed energy technologies. These techniques melt a powder or wire and deliver it to the area where metal deposition is desired and build the article layer by layer.

Many titanium alloys can be processed using these additive manufacturing methods, most commonly Ti-6 Al-4V. Although the processing details discussed herein are understood to relate to this particular alloy, this is not meant to be limiting as the invention will find broad applicability in many titanium alloys.

Common throughout these techniques is an improved method and technique that enables rapid melting and cooling of relatively small areas in the article being built, referred to herein as "selective melting". In many cases, the entire article is constructed of materials that have undergone these thermal cycles. Also, since the article is directionally built, selective melting can lead to unwanted anisotropy, and associated differences in mechanical properties when tested in different directions.

The present disclosure provides for the application of hot hydrogen technology to all manufactured titanium articles, and in some cases those manufactured specifically by additive manufacturing methods, to mitigate the anisotropy present in the article, effectively homogenize the microstructure of the titanium, and overcome the deleterious effects of oxygen and layered microstructures. The present disclosure also relates to articles obtained using hot hydrogen technology. This disclosure is directed to various inventive embodiments described in this section and others.

Aspect A:

in one aspect of the present invention, referred to herein as aspect a, a method for improving the physical properties of a base titanium alloy article previously manufactured by a selective melting process is disclosed. The method of aspect a includes introducing hydrogen into a base titanium alloy article via a hot hydrogen process, the resulting titanium alloy article exhibiting an equiaxed microstructure of isotropic and refined grains.

In aspect a, the base titanium alloy article may exhibit more anisotropy and coarser grain quality than the resulting titanium article.

In aspect a or any of the foregoing modifications, the resulting titanium alloy article may exhibit an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 100 microns.

In aspect a or any of the foregoing modifications, the resulting titanium alloy article may exhibit an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 50 microns.

In aspect a or any of the foregoing modifications, the resulting titanium alloy article may exhibit an equiaxed microstructure of isotropic and refined grains, having a grain size of less than 20 microns.

In aspect a or any of the foregoing modifications, the resulting titanium alloy article may exhibit an equiaxed microstructure of isotropic and refined grains, the grain size being less than 10 microns.

In aspect a or any of the foregoing modifications thereof, the step of introducing hydrogen by a hot hydrogen process may include introducing hydrogen into the base titanium alloy article to reduce the beta transus temperature; heating the base titanium alloy article above the reduced beta transus temperature to form hydrogenated beta; reducing the temperature of the base titanium alloy article to affect eutectoid transformation; the base titanium alloy article is dehydrogenated by vacuum heating.

In aspect a or any one of the preceding improvements thereof, the step of heating the base titanium article above the reduced β transus temperature to form hydrogenated β can be carried out in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect a or any one of the foregoing modifications thereof, the temperature resulting from the step of dehydrogenating the base titanium alloy article by vacuum heating may be conducted in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect a or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.4 wt.% hydrogen or more.

In aspect a or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.5 wt.% hydrogen or more.

In aspect a or any one of the foregoing modifications thereof, the step of introducing hydrogen may be from 0.5 weight percent hydrogen to 1.5 weight percent hydrogen.

In aspect a or any of the foregoing modifications thereof, the oxygen content of the base titanium alloy article may be greater than any of 2000ppm, 2500ppm, 3000ppm, 3500ppm, and 4000 ppm.

In aspect a or any of the foregoing modifications thereof, the base titanium alloy article may be a surgical implant.

In aspect a or any of the foregoing modifications, the base titanium alloy article may be a hip stem.

In aspect a or any of the foregoing improvements thereof, the resulting titanium alloy article may exhibit fatigue properties comparable to or superior to a wrought material of the same titanium alloy.

In aspect a or any of the foregoing modifications thereof, the base titanium alloy article may be fabricated from a first entity and the step of introducing hydrogen by a thermal hydrogen process may be performed from a second entity.

In aspect a or any of the foregoing modifications thereof, the base titanium alloy article may be manufactured in a first apparatus and the step of introducing hydrogen by a thermal hydrogen process may be performed in a separate apparatus remote from the first apparatus.

Aspect a or any of the foregoing modifications thereof may further comprise subjecting the base article or the resulting article to hot isostatic pressing.

Aspect a or any of the foregoing modifications thereof may further comprise subjecting the base article to hot isostatic pressing prior to the step of introducing hydrogen.

Aspect B:

in another aspect of the invention, referred to herein as aspect B, a method for processing a selectively melted titanium article is disclosed. The method of aspect B includes introducing hydrogen into the article to reduce the beta transus temperature of the article; heating the article above the reduced beta transus temperature to form hydrogenated beta; reducing the temperature of the article below the eutectoid transition point; and dehydrogenating the article by vacuum heating to obtain a processed article.

In aspect B, the step of heating the article above the reduced β transus temperature to form a hydrogenated β phase may be performed in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below or +/-3 ℃ or below.

In aspect B or any one of the preceding modifications thereof, the step of dehydrogenating the article by vacuum heating to form the worked article may be performed in a furnace having any one of the following temperature uniformities: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below or +/-3 ℃ or below.

In aspect B or any of the foregoing modifications thereof, the grain size of the processed article may be smaller than the grain size of the unprocessed article.

In aspect B or any of the foregoing modifications, the grain size of the worked article may be less than 100 microns.

In aspect B or any of the foregoing modifications, the grain size of the worked article may be less than 50 microns.

In aspect B or any of the foregoing modifications, the grain size of the worked article may be less than 20 microns.

In aspect B or any of the foregoing modifications, the grain size of the worked article may be less than 10 microns.

Aspect B or any of the foregoing modifications thereof may further comprise subjecting the article or fabricated article to hot isostatic pressing.

Aspect B or any of the foregoing modifications thereof may further comprise subjecting the article to hot isostatic pressing prior to the step of introducing hydrogen.

Aspect B or any of the foregoing modifications thereof may further comprise annealing the article prior to the step of introducing hydrogen.

In aspect B or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.4 wt% hydrogen or more.

In aspect B or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.5 wt% hydrogen or more.

In aspect B or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.5 to 1.5 wt% hydrogen.

In aspect B or any of the foregoing modifications thereof, in the step of heating the article above the lower β transus temperature, the article may be heated to 10 ℃ to 75 ℃ above the transus temperature to form a hydrogenated β phase.

In aspect B or any of the foregoing modifications thereof, the temperature resulting from the step of heating the article above the reduced β transus temperature to form the hydrogenated β phase may be maintained for 30 to 60 minutes.

In aspect B or any one of the foregoing modifications thereof, the temperature resulting from the step of lowering the temperature of the article below the eutectoid transformation point may be maintained for 3 to 6 hours.

In scheme B or any of the foregoing modifications thereof, the step of dehydrogenating the article by vacuum heating to form the fabricated article can be performed between 650 ℃ and 850 ℃ for 2 to 48 hours.

In aspect B or any one of the foregoing modifications thereof, the step of introducing hydrogen may introduce 0.5 to 1.5 wt.% hydrogen; in the step of heating the article above the reduced beta transus temperature to form a hydrogenated beta phase, the article may be heated to 10 ℃ to 75 ℃ above the beta transus temperature; the temperature resulting from the step of heating the article above the reduced beta transus temperature to form a hydrogenated beta phase may be maintained for 30 to 60 minutes; the temperature resulting from the step of lowering the temperature of the article below the eutectoid transition point can be maintained for 3 to 6 hours; and the step of dehydrogenating the article by vacuum heating to form the worked article may be performed between 650 ℃ and 850 ℃ for 2 to 48 hours.

In aspect B or any of the foregoing modifications thereof, the oxygen content of the article may be greater than any of 1300ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, or 4000 ppm.

In aspect B or any of the foregoing modifications thereof, the article of manufacture may be a surgical implant.

In aspect B or any of the foregoing modifications, the article may be a hip stem.

In aspect B or any of the foregoing modifications thereof, the worked article may exhibit fatigue properties equivalent to or superior to a wrought material of the same titanium alloy.

Aspect C:

in another aspect of the present invention, referred to herein as aspect C, the titanium alloy article produced comprises an oxygen content greater than 2000 ppm; refining the equiaxed microstructure of the grains; and, a grain size of less than 100 microns.

In aspect C or any of the foregoing modifications, the article may comprise an isotropic microstructure.

In aspect C or any one of the foregoing modifications, the grain size may be less than 50 microns.

In aspect C or any one of the foregoing modifications, the grain size may be less than 20 microns.

In aspect C or any one of the foregoing modifications, the grain size may be less than 10 microns.

In aspect C or any of the foregoing modifications thereof, the equiaxed microstructure of the refined grains may be a result of the thermal hydrogen treatment.

In aspect C or any of the foregoing modifications thereof, the oxygen content may be greater than 2500ppm, 3000ppm, 3500ppm, or 4000 ppm.

In aspect C or any one of the foregoing modifications thereof, the article of manufacture may be a surgical implant.

In aspect C or any of the foregoing modifications, the article may be a hip stem.

In aspect C or any of the foregoing modifications, the article may exhibit fatigue properties equivalent to or better than a wrought material of the same titanium alloy.

In aspect C or any one of the foregoing modifications, the article may be a high strength titanium article.

Aspect D:

in another aspect of the invention, referred to herein as aspect D, a method for improving the physical properties of a base titanium alloy article having an increased oxygen content is disclosed. The method of aspect D includes introducing at least 0.4 wt.% hydrogen to the base titanium alloy article to lower the beta transus temperature, heating the article above the reduced beta transus temperature to form a hydrogenated beta, lowering the temperature of the article to effect a eutectoid transformation, dehydrogenating the article by vacuum heating to form a resulting article; the resulting article exhibits an equiaxed microstructure of refined grains, the grain size being less than 100 microns; wherein the increased oxygen content (elongated oxygen content) is above 2000 ppm.

In aspect D or any of the foregoing modifications thereof, the resulting article may exhibit an isotropic microstructure.

In aspect D or any of the foregoing modifications, the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

In aspect D or any of the foregoing modifications, the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

In aspect D or any of the foregoing modifications, the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

In aspect D or any one of the foregoing modifications thereof, the step of heating the article above the reduced β -transus temperature can be performed in an oven having a temperature uniformity of any one of: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect D or any one of the foregoing modifications thereof, the step of dehydrogenating the article by vacuum heating may be performed in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect D or any one of the foregoing modifications thereof, the step of introducing hydrogen may be at least 0.5 wt.% hydrogen.

In aspect D or any one of the foregoing modifications thereof, the step of introducing hydrogen may be from 0.5 wt.% hydrogen to 1.5 wt.% hydrogen.

In aspect D, the step of heating the article above the reduced β transus temperature can be performed in an oven having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below; the step of dehydrogenating the article by vacuum heating may be performed in a furnace having any of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below; and, the step of introducing hydrogen may be from 0.5 wt% hydrogen to 1.5 wt% hydrogen.

In aspect D or any of the foregoing modifications thereof, the increased oxygen content may be greater than any of 2500ppm, 3000ppm, 3500ppm, and 4000 ppm.

In aspect D or any one of the preceding improvements thereof, the titanium alloy article may be a surgical implant.

In aspect D or any of the foregoing modifications, the titanium alloy article may be a hip stem.

In aspect D or any of the foregoing modifications, the titanium alloy article may exhibit fatigue properties equivalent to or superior to a wrought material of the same titanium alloy.

In aspect D or any one of the foregoing modifications, the titanium alloy article may be a high-strength titanium alloy article.

Aspect E:

in another aspect of the invention, referred to herein as aspect E, a method for improving the physical properties of a titanium alloy article is disclosed. The method of aspect E includes introducing at least 0.4 wt.% hydrogen to the titanium alloy article to reduce the beta transus temperature; heating the article to a temperature above the reduced beta transus temperature to form hydrogenated beta, the heating being in a furnace having a temperature uniformity of +/-28 ℃ or less; lowering the temperature of the article to effect eutectoid transformation; dehydrogenating the article by vacuum heating to form a resulting article; wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 100 microns.

In aspect E or any of the foregoing modifications, the step of introducing hydrogen to the titanium alloy article to reduce the β transus temperature may introduce at least 0.5 wt.% hydrogen.

In aspect E or any of the foregoing modifications, the step of introducing hydrogen to the titanium alloy article to reduce the β transus temperature may introduce 0.5 wt.% hydrogen and 1.5 wt.% hydrogen.

In aspect E or any of the foregoing modifications, the resulting article exhibits an isotropic microstructure.

In aspect E or any of the foregoing modifications thereof, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

In aspect E or any of the foregoing modifications thereof, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

In aspect E or any of the foregoing modifications thereof, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

In aspect E or any of the foregoing modifications, the oxygen content of the titanium alloy article may be in excess of 2000 ppm.

In aspect E or any of the foregoing modifications, the oxygen content of the titanium alloy article may exceed 3000 ppm.

In aspect E or any one of the preceding improvements thereof, the step of heating the article above the reduced β -transus temperature to form the hydrogenated β can be performed in a furnace having any one of the following temperature homogeneity: +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below or +/-3 ℃ or below.

In aspect E or any one of the preceding modifications thereof, the step of dehydrogenating the article by vacuum heating may be performed in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect E or any of the foregoing modifications thereof, the resulting article may exhibit fatigue properties comparable to or better than a wrought material of the same titanium alloy.

In aspect E or any of the foregoing modifications thereof, the article produced may be a surgical implant.

In aspect E or any of the foregoing modifications thereof, the article produced may be a hip stem.

Aspect F:

in another aspect of the invention, referred to herein as aspect F, a method for improving the physical properties of a titanium alloy article is disclosed. The method of aspect F includes introducing at least 0.4 wt.% hydrogen into the titanium alloy article to reduce the beta transus temperature; heating the article above the reduced beta transus temperature to form hydrogenated beta; lowering the temperature of the article to effect eutectoid transformation; dehydrogenating the article by vacuum heating to form the resulting article, the vacuum heating being in a furnace having a temperature uniformity of +/-28 ℃ or less; wherein the resulting article exhibits an equiaxed microstructure of refined grains, having a grain size of less than 100 microns.

In aspect F or any of the foregoing modifications, the step of introducing hydrogen to the titanium alloy article to lower the β transus temperature may introduce at least 0.5 wt.% hydrogen.

In aspect F or any of the foregoing modifications, the step of introducing hydrogen to the titanium alloy article to reduce the β transus temperature may introduce 0.5 wt.% hydrogen to 1.5 wt.% hydrogen.

In aspect F or any of the foregoing modifications thereof, the resulting microstructure can exhibit an isotropic microstructure.

In aspect F or any of the foregoing modifications, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 50 microns.

In aspect F or any of the foregoing modifications, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 20 microns.

In aspect F or any of the foregoing modifications, the resulting article may exhibit an equiaxed microstructure of refined grains, having a grain size of less than 10 microns.

In aspect F or any of the foregoing modifications, the oxygen content of the titanium alloy article may exceed 2000 ppm.

In aspect F or any of the foregoing modifications, the oxygen content of the titanium alloy article may exceed 3000 ppm.

In aspect F or any one of the preceding modifications thereof, the step of heating the article above the reduced β -transus temperature to form hydrogenated β can be performed in a furnace having any one of the following temperature homogeneity: +/-28 ℃ or below, +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect F or any one of the preceding modifications thereof, the step of dehydrogenating the article by vacuum heating may be performed in a furnace having any one of the following temperature homogeneity: +/-14 ℃ or below, +/-10 ℃ or below, +/-8 ℃ or below, +/-6 ℃ or below, or +/-3 ℃ or below.

In aspect F or any of the foregoing modifications thereof, the resulting article may exhibit fatigue properties comparable to or better than a wrought material of the same titanium alloy.

In aspect F or any of the foregoing modifications thereof, the article produced may be a surgical implant.

In aspect F or any of the foregoing modifications, the resulting article may be a hip stem.

Drawings

The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The organization and method of operation, however, together with features, objects, and advantages thereof will become apparent to those skilled in the art upon reference to the following detailed description when read with the accompanying drawings. It is intended that all such additional structures, methods of operation, features, objects, or advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

With respect to the figures, fig. 1 depicts a comparison of macrostructures produced by different additive manufacturing techniques;

FIG. 2 depicts a selectively melted Ti-6Al-4V material exhibiting anisotropic perpendicular grain orientation;

FIG. 3 depicts the selectively melted Ti-6Al-4V material of FIG. 2 after thermal hydrogen treatment;

FIG. 4 depicts a selectively melted Ti-6Al-4V material annealed at 800 ℃ for 1 hour;

FIG. 5 depicts a selectively melted Ti-6Al-4V material, first annealed at 800 ℃ for 1 hour, then HIP at 900 ℃ for 2 hours;

FIG. 6 depicts a selectively melted Ti-6Al-4V material first annealed at 800 ℃ for 1 hour, HIP at 900 ℃ for 2 hours, and then subjected to a thermal hydrogen treatment;

FIG. 7 is a higher magnification view of the material in FIG. 5; and

fig. 8 is a higher magnification view of the material in fig. 6.

Detailed Description

The following describes preferred embodiments of the microstructural improvement of the titanium alloy according to the invention. In describing the embodiments illustrated in the drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. Similar elements are described in the various embodiments, and the same reference numerals are used in the various embodiments to facilitate understanding.

The term "selective melting" has been used or is to be used throughout this disclosure. For clarity of understanding, it should be understood that the use of the term "selective melting" is intended to include all additive manufacturing techniques that incorporate a melting event. The term "additively manufactured" should be construed to broadly include all additively manufactured articles, including those that are selectively melted and those that are not.

As discussed previously, the additively manufactured titanium articles exhibit anisotropy when tested in different directions, resulting in differences in mechanical properties.

The problem of anisotropy is well known in the industry. To alleviate this difficulty, it is well known that the microstructure can be moderately modified using conventional processes such as Hot Isostatic Pressing (HIP) or annealing. It is also well known that these processes have their inherent limitations, some of which are discussed below.

Titanium is commonly used in medical or aerospace applications where fatigue performance is critical. However, selectively melted articles generally exhibit residual porosity that is detrimental to fatigue performance, which is considered unacceptable in medical or aerospace applications. To remove this residual porosity, it is known to subject the article to hot isostatic pressing. However, the thermal cycling associated with the hot isostatic pressing process may negatively affect the microstructure because the article must survive longer periods of time at higher temperatures.

The thermal cycling associated with hot isostatic pressing increases grain size and produces a coarser, elongated alpha structure. This structural change is generally beneficial for increasing ductility, but it is understood that tensile strength is reduced. From the viewpoint of fatigue strength, a decrease in tensile strength is particularly undesirable. In any case, the anisotropy persists after hot isostatic pressing, and these parts still exhibit a columnar grain structure.

Challenges exist in creating non-porous articles that retain relatively high tensile strength and a microstructure suitable to provide good fatigue performance. The microstructure produced by the technique of the present invention is truly unique in the world of selective melting of titanium.

The nature of these microstructures depends on a number of variables depending on the specific process parameters, the specific article geometry, and the specific consolidation technique used. There are many process variables including the deposition rate, the scan rate of the energy source, and the intensity of the energy source. The product has portions of different thickness, thereby creating hot spots or heat sinks, changing the thermal conditions at different portions in the same part. Different techniques use different energy sources, raw materials and deposition methods, all of which affect the microstructure. It is important to note that microstructural changes occur not only between different process settings or manufacturing techniques, but also within a single article.

There are many different techniques for manufacturing titanium metal articles by selective melting, including Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), laser near net shape forming (LENS), laser metal powder deposition (LMpD), laser wire deposition (LMwD), Shaped Metal Deposition (SMD), Selective Laser Sintering (SLS), and Selective Laser Melting (SLM).

Low magnification metallographic images such as those in fig. 1 are sometimes referred to as macrostructures. Macrostructures are particularly useful for viewing large scale orientations. Figure 1 shows macrostructures from several different additive process technologies, namely, Shaped Metal Deposition (SMD), Electron Beam Melting (EBM), Selective Laser Melting (SLM), continuous laser wire deposition (LMwD-0), laser wire deposition with 2 minute intervals (LMwD-2), and laser metal powder deposition (LMpD). Although the specific nature of the microstructures varies from image to image, these microstructures all have layered or highly oriented structures.

As can be seen from a comparison of fig. 1, a number of different microstructures are also seen. The microstructure can be large columnar grains, small columnar grains, equiaxed grains, and mixtures of these types. Indeed, the deviation of the microstructure towards complete equiaxial has proven difficult in practice, since controlling the process parameters of these equiaxial oriented microstructures means exchanging other properties of the finished product, such as tensile strength, ductility and layer adhesion (layer adhesion).

Controlling the degree of equiaxed versus columnar structure can be achieved by varying process parameters such as deposition rate, scan rate, and energy level, but at the expense of other material properties or commercial considerations (e.g., build time).

Extensive development efforts have been applied to overcome these difficulties and control variables to produce relatively predictable microstructures. In practice, however, it is difficult to achieve a microstructure that is both predictable and satisfactory, and it is impossible to produce a desired microstructure.

It would therefore be desirable to provide a method of homogenizing these microstructures in a single article to provide a consistent microstructure in the article while providing mechanical properties equal to or superior to the original article. The second heat treatment, which is capable of simultaneously homogenizing and improving the microstructure, is widely used to expand the use of selectively melting titanium products to more demanding applications.

Due to the extreme thermal stresses applied to the article during the manufacturing process by many melting, cooling, and remelting cycles, it is generally considered necessary to anneal the components prior to delivery for use or even prior to removing the article from the build platform. In fact, bench cracking (bench cracking) sometimes occurs before annealing of the part.

Thus, and very conventionally, the microstructure may also be homogenized using thermal cycling, for example by vacuum or inert atmosphere annealing. Typical low temperature anneal conditions in the range of 500-650 deg.c do not eliminate the columnar structures but do eliminate some of the fabrication related stresses. High temperature annealing, typically around 800 ℃, alters the microstructure more greatly, coarsens the grain size and produces less elongated alpha structures, but does not eliminate the macro columnar structures.

The grain coarsening associated with annealing and the retained high aspect ratio alpha grains can negatively impact mechanical properties. As with the variations seen in the HIP cycle, the growth of elongated alpha structures slightly increases elongation, but has the deleterious effect of reducing tensile properties. Furthermore, the larger grain size and elongated alpha structure are understood to have a negative impact on fatigue performance.

What is desired is a method for eliminating anisotropic mechanical properties while not reducing or preferably improving the mechanical properties of the material relative to the starting material.

What is also desired is a method of homogenizing a microstructure in a component, construction or process.

What is also desired is a non-porous article having a homogeneous, isotropic, and refined microstructure.

From a purchasing perspective, it is desirable for the buyer to purchase articles from different additive manufacturing sellers, and then have the ability to process the parts to ensure consistent properties. In other words, the processes disclosed herein may be well applied after the additive manufactured article is completed, including when the article is shipped to an entity other than the manufacturer. For example, a base titanium article may be manufactured from a first entity, and then a subsequent step of introducing hydrogen by a thermal hydrogen treatment process is performed by a second entity. Alternatively, the base titanium article may be manufactured at a first facility, and then the subsequent step of introducing hydrogen by thermal hydrogen treatment may be performed at a second facility remote from the first facility, from the same entity or a different entity.

Thermal hydrogen treatment is a well-known process for refining the grain size of titanium articles manufactured by non-additive manufacturing methods such as casting and powder metallurgy. Using thermal hydrogen treatment, grain size refinement is improved by incorporating hydrogen as a temporary alloying element during the thermal treatment. The present disclosure and the invention defined herein demonstrate that thermal hydrogen treatment can also be successfully applied to titanium articles additively manufactured by selective melting techniques, not only to refine grain size, but also to eliminate isotropic microstructure without degrading mechanical properties.

Prior applications of these techniques focused on refinement of the microstructure without mitigating or eliminating large scale orientation, columnar microstructure, or anisotropic microstructure. As described, the selectively melted microstructure is unique and can vary greatly from single part, batch, or process to process. Due to the novelty and significant difference from conventionally manufactured titanium components, it was not clear to practitioners in the art prior to this disclosure that the hot hydrogen treatment techniques are applicable to the microstructural challenges of additively manufactured titanium components.

In fact, since additive manufacturing is a relatively new technology, one does not have a good understanding of the resulting microstructures, nor of the reaction of these microstructures to different subsequent manufacturing processes. The microstructure has also proven to be unpredictable. The microstructure is subject to many variables between the type of machine, the specific geometry, and the specific process settings. It is challenging to accurately predict what microstructure features will be produced and how these microstructures will conform on an article, let alone how the microstructures will handle heat treatment after the article is additively manufactured.

Thermal hydrogen treatment is subject to many variations and is known under many different names, including thermal hydrogen Treatment (THP) and Thermal Hydrogen Treatment (THT). Regardless of the name, thermal hydrogen treatment includes the general steps of introducing hydrogen into the article to control the microstructure and then removing the hydrogen. The control of the microstructure is a result of hydrogen and temperature changes, and the purpose of this discussion does not include processes involving mechanical deformation to alter the microstructure. A typical cycle includes the following general steps: hydrogen is introduced into the article to control the microstructure, then the hydrogen is removed to lower the beta transus temperature, the article is heated above the new reduced beta transus temperature to form hydrogenated beta, the temperature of the article is reduced to affect the eutectoid transformation, and then the article is dehydrogenated by vacuum heating.

Technically, at least 0.4 wt.% hydrogen is required to achieve the beta transus temperature reduction. In practice, the hydrogen is typically introduced at 0.5 wt% hydrogen or higher. Addition of more than 0.5 wt.% hydrogen does not further lower the transition temperature. Additions well above 1.5 wt% can lead to cracking of the article.

Once the article is hydrogenated, the temperature is raised above the new transition temperature. Although the lowest temperature rise above the transition temperature is not understood, in practice the article is heated to 10 ℃ to 75 ℃ above the transition temperature to ensure that the transition is exceeded. It is understood that it is important to heat the article above the transition temperature to allow for the most full development of the hydrogenated beta phase. This is also referred to as the beta solutionizing step. The kinetics of this step are relatively fast and the time above the transition temperature is not considered to be particularly critical. In practice, the temperature is maintained for 30 to 60 minutes. Also, discrete hold may not be necessary if a very slow ramp rate is used.

The article is then reduced in temperature to transform the eutectoid. Because the kinetics here are relatively slow, the cooling rate is not critical, but is understood to be in the range of 3-15 deg.C/min. Because of the lower temperature, kinetics are slower, and the holding time can range from 0 to 6 hours, but more typically, 2 to 4 hours. In fact, slow cooling through the decomposition window (decomposition window) may provide an effective eutectoid decomposition (eutectoid decomposition).

The article is then heated in a vacuum to remove the hydrogen. The time and temperature for optimized vacuum removal of hydrogen depends on the thickness of the part, with thicker parts requiring higher temperatures and/or longer heating vacuum times. Typical dehydrogenation conditions are maintained at 650 ℃ to 850 ℃ for 2 to 48 hours. The preferred dehydrogenation temperature is between 700 ℃ and 800 ℃. Cross-sections up to 1 inch are reported to be treatable in this manner.

As discussed above, the thermal hydrogen treatment was demonstrated to refine the grain size of the titanium microstructure formed by the non-additive manufacturing method. Similar methods are employed in additive manufacturing of titanium parts using selective melting and starting with columnar grains having a major length in excess of 500 microns, it has been shown that articles can exhibit a finished grain size of less than 50 microns.

It has also been shown that the article can exhibit a finished grain size of less than 20 microns. The finished product may also exhibit a finished grain size of less than 10 microns. The present study shows that these techniques can also eliminate anisotropic microstructures previously introduced during the layer-by-layer build of the article. Thus, the article exhibits equiaxed microstructures that are isotropic and refined in grains, including those microstructures less than 50 microns, less than 20 microns, and less than 10 microns. One of the challenges in selective melting is that the predictability and controllability of the pores is low when the pore frequency is less than that of other powder technologies. To ensure that there are no detrimental levels of porosity, these components can be HIP treated.

Therefore, additive manufactured titanium components are typically HIP treated to eliminate residual porosity. A typical HIP treatment for titanium is heating to approximately 900 ℃ and 100MPa for 2 hours. This is the most common cycle for HIP titanium, and adjusting the temperature or pressure can improve the microstructure, as will be apparent to those skilled in the art. In particular, lower temperatures may produce better microstructures but require higher pressures.

Another advantage of the present invention is that the thermal hydrogen treatment can be used to homogenize and refine the microstructure of the HIP component to present a fully compact article having a homogeneous macro and microstructure and refined grain size. Although microscopic porosity may occasionally be present, the term "fully compact" is understood to mean that the article has been successfully HIP treated, the article having a density of 99.5% or greater.

Example 1-following are exemplary steps according to the present invention.

The additively manufactured Ti-6Al-4V article was first annealed at 590 ℃ for 1 hour to relieve the stresses induced in the additive manufacturing process. The article was then subjected to a hot hydrogen treatment to hydrogenate the element to a hydrogen content of 0.65 wt% at 785 c. Hydrogen is a beta stabilizer, lowering the transition temperature to near 800 ℃. Thus, the article may undergo beta solutionizing below the transformation temperature of the original, unhydrogenated alloy. It should also be understood that although 785 ℃ is used in this example, hydrogenation may occur over a wide temperature range including between 740 ℃ and 790 ℃. These temperatures are understood to be in an environment of primarily hydrogen. Partial pressure of hydrogen and mixed atmospheres can be used to control these temperatures.

In this example, the article was subjected to a beta solution treatment in hydrogen at 825 ℃ for 1 hour. It should also be understood that while 825 c is used in this example, beta solutionizing may occur over a wide temperature range including between 815 c and 875 c. Thereafter, the reaction mixture was kept at 580 ℃ for 6 hours in an argon atmosphere to effect eutectoid transformation. After this step, the removal of hydrogen was performed by vacuum heating at 700 ℃ until hydrogen was removed. It should also be understood that while 700 ℃ is used in this example, dehydrogenation can occur over a wide temperature range including between 670 ℃ and 750 ℃.

Fig. 2 shows an article of additive construction prior to thermal hydrogen treatment. It can be clearly seen that the microstructure exhibits a strong directionality. This is due to layered fabrication technology (layered fabrication technique). It should also be noted that this material was heated at 590 ℃ for 1 hour for stress relief prior to removal from the build platform.

Figure 3 shows the same article as figure 2 after treatment using the thermal hydrogen technique of the present invention. It is clear from a comparison of the figures that the directionality of the microstructure is eliminated. Although some prior grain boundaries were visible, a comparison of the mechanical properties of the original material and the treated material showed that the mechanical properties were not reduced, and actually improved, except for homogenization of the microstructure. Grain size has been greatly reduced from over 100 microns to below 10 microns.

TABLE 1 comparison of tensile Properties

Condition	UTS(ksi)	Y.S.(ksi)	Elongation (%)
				Typical minimum specification	130	120	10
Selective melting and stress relief annealing (FIG. 7)	190	173	4
				After the thermal hydrogen treatment (FIG. 8)	150	139	12

Table 1 compares the mechanical properties of the same material after selective melting of Ti-6A-4V and thermal hydrogen treatment, including Ultimate Tensile Strength (UTS), yield strength (Y.S.) and elongation, while also providing conventional material specifications.

The untreated selectively melted element exhibited very high tensile strength (190ksi), but was very brittle with an elongation of only 4%. In most industry specifications, the minimum elongation of such an alloy is specified to be 10%. Although the tensile strength is higher than the typical minimum specification of 130ksi, the brittleness of the material is unacceptable compared to the industry standard of Ti-6 Al-4V.

Ti-6Al-4V alloys have many specifications, which are slightly different in industry and manufacturing method. The values shown in table 1 are representative values for most specifications. Selectively melted components do not meet specifications and cannot be used in demanding applications.

These parts were then subjected to hot hydrogen treatment, which proved to show very good tensile values, although slightly lower than before treatment, but now also meeting the elongation requirements compared to typical specification limits. The treatment homogenizes the microstructure and eliminates anisotropy while balancing mechanical properties to provide a strong but ductile product. In this regard, some reduction in ultimate tensile strength is acceptable in view of the concomitant increase in elongation, as the material still meets specification requirements.

Discussion of HIP:

hot isostatic pressing may be employed to remove residual porosity if required due to the end use of the material. In general, Ti-6Al-4V is subjected to HIP treatment by heating at 900 ℃ for 2 hours while applying a pressure of 100MPa by an inert gas. Due to the near-beta transition and the elevated temperature, the grains may become coarse during operation, and during coarsening, plates (plates) and laths (laths) may grow. The highest aspect ratio elements of the microstructure are believed to have an adverse effect on the performance index. Furthermore, tensile properties are generally reduced and elongation is increased.

One problem is that in order to eliminate the porosity that is critical for fatigue, the component must be subjected to thermal conditions that affect microstructural changes that are detrimental to fatigue. After the HIP cycle, the hot hydrogen technology is adopted, so that not only can the microstructure be homogenized to eliminate anisotropy, but also the microstructure can be refined, the sheet structure can be damaged, and better fatigue performance can be provided.

FIG. 4 shows selectively melted Ti-6Al-4V annealed at 800 deg.C, with dimensions of 250 μm. For comparison, FIG. 5 shows the same selectively melted and annealed Ti-6Al-4V after HIP at 900 ℃.

Fig. 4 shows a highly columnar structure with relatively fine grains inside the columns. This structure has more alpha grains than the microstructure in fig. 2 due to the higher temperature anneal. It is still possible to have residual porosity because HIP has not been performed.

The annealed and HIP material in FIG. 5 exhibits coarsened grains that reduce tensile strength and fatigue performance. Moreover, oriented, anisotropic columnar structures remain evident.

Fig. 6 shows the same material as fig. 5 after thermal hydrogen treatment. It is desirable to eliminate anisotropic structures with average grain sizes less than 50 microns.

FIG. 7 depicts a higher magnification image of the annealed and HIP structure of FIG. 5. Despite the relatively small grains, there are many elongated platelet elements. These are known to be detrimental to fatigue performance.

Fig. 8 depicts a higher magnification image of the selectively melted and annealed material of fig. 6. In comparison to fig. 7, the elongated alpha structure has been eliminated in fig. 8, the grain size is refined and the microstructure is more homogeneous.

Fig. 8 shows highly refined grains, without the presence of elongated alpha structures. This represents a dramatic improvement in the microstructure behavior, as these improvements tend to make the material more fatigue-resistant than under the sintering, annealing and HIP conditions.

The fatigue properties of these materials were evaluated using a rotating beam method. Typically, these tests are performed on r.r.moore type test equipment using unnotched samples. The variation was evaluated over a million cycles. The non-homogenized article, selectively melt annealed and then HIP'd, exhibited the microstructure of FIG. 7, which exhibited a fatigue strength of 70 ksi. The same material after homogenization by hot hydrogen treatment (as depicted in fig. 8) exhibited a fatigue strength of 93 ksi. The fatigue performance is improved by more than 30 percent. This is also commercially significant because the performance of a typical wrought plate (wrought plate) is met or exceeded.

Discussion of elevated oxygen content:

by increasing the oxygen content of the alloy, the fatigue properties can be further improved over those obtained by thermal hydrogen treatment alone. While oxygen is understood to be a solid solution strengthener in titanium alloy systems, in general, it is also understood to be detrimental to the fatigue properties and fracture resistance of these alloys. Typically, oxygen is limited to 1300ppm or 1500ppm, with occasional allowances of up to 2000 ppm. High strength titanium alloys with oxygen levels above 2000ppm are not specified for use in performance critical applications.

Higher oxygen content limits can be found in some casting specifications, but castings of these specifications are unsuitable for critical applications, having lower mechanical properties, especially lower elongation. Exceptions have also occurred with titanium materials that are non-alloyed and very low alloyed (less than 1%). These materials have a special purpose and are not considered high strength materials. As a general guideline, high strength titanium articles have a combination of a minimum yield strength of 105ksi, a minimum ultimate tensile strength of 120ksi, and a minimum elongation of 8%.

The use of increasing oxygen content to enhance Ti-6Al-4V is disclosed by Abkowitz in US20140377119A 1. Sintered and sintered HIP microstructures are disclosed. Figure 1 in Abkowitz shows a layered (lamellar) structure.

Increased oxygen levels contemplated in this disclosure include those ranging from approximately 2000ppm to over 4000ppm, including any number within the range, specifically 2500ppm, 3000ppm, 3500ppm, or over 4000 ppm.

As an example, a Ti-6Al-4V alloy with sintered and HIP having an oxygen content of 3000ppm would demonstrate very good static tensile properties, an ultimate tensile strength of 145ksi, a yield strength of 135ksi, and an elongation of 18%. However, the fatigue properties of such materials are unacceptably low. After the end of one million cycles, this material demonstrated a fatigue performance of 60 ksi.

The microstructure of the Ti-6Al-4V alloy accompanying sintering and HIP is in fact lamellar and is understood to perform best under static conditions but not under dynamic conditions.

However, by applying a hot hydrogen treatment to additively manufacture Ti-6Al-4V articles with increased oxygen content, the material is refined and equiaxed and the drawbacks of its original layered structure can be circumvented, exhibiting improved dynamic performance.

The improved microstructure by the hot hydrogen treatment was experimentally shown to improve fatigue performance to 98ksi or higher with an increase of over 60%. The improvement in microstructure converts this material from a poor quality material to a good material, representing the value and utility of the teachings of the present disclosure. Another performance improvement can be seen at oxygen levels in excess of 3500, 4000 and 4500 ppm.

This is significant because the conventional thinking of the effect of oxygen on the fatigue performance of titanium and titanium alloys is contrary. While improvements in static tensile properties have long been known, improvements in static tensile properties have been considered to be accompanied by a substantial reduction in dynamic and fatigue properties.

This teaching has a solid foundation. The fatigue properties of titanium alloys with high oxygen content have been consistently demonstrated to be poor. An important nuance in the prior art is the particular refinement of the high oxygen content material by the thermal hydrogen process to provide an improved microstructure.

Powder-based additive manufacturing is particularly suitable for producing materials with an increased oxygen content, since the oxygen content of the raw material is easier to control than conventional roller compacted articles. One way to achieve this goal is to mix oxide particles or alloy particles with a high oxygen content and a powder with a conventional oxygen content to achieve the desired final oxygen content. Another method involves oxidizing the raw materials or formed parts or providing higher oxygen content in the abrasive as the raw material for the powder manufacturing operation.

Increasing oxygen while improving microstructure through chemical treatment can have a number of advantages not previously expected. The microstructural improvement accompanied by the hot hydrogen treatment allows the alloy to overcome previously accepted belief that oxygen is inherently detrimental to fatigue performance and provide suitability for a wide range of applications previously thought impossible.

A unique aspect of the present invention is the ability to improve performance without changing the metal composition of the alloy, thereby improving the utility of a given alloy.

By way of example, Ti-6Al-4V alloys have become the world's poor college (workphouse) in the medical implant industry because of their availability and strength, rather than being specifically adapted for any particular implant application. Indeed, many other alloys have been developed with improvements that have been demonstrated over Ti-6Al-4V alloys. These improvements include alloy compositions with more biocompatibility for the skeleton or better matched alloy moduli. However, these materials are rarely used because of the incredible high cost of new alloys that are acceptable for human implants.

The surgical implant industry is generally limited from a fatigue perspective by the Ti-6Al-4V alloy. Many total joint replacement components have very demanding fatigue performance requirements, of which the excellent example is the hip stem. The functional space of total joint replacement surgery is limited by the anatomy, and it is often desirable to make smaller joints or to allocate certain functional areas of the joint, such as the bearing surface, a larger volume than other areas of the replacement joint. However, the structural area of the joint must retain enough material to perform its function, which often limits its design. Making these joints smaller and more minimally invasive, or improving the desire to design them, is hindered by the physical properties of the Ti-6Al-4v alloy.

The design window of Ti-6Al-4V is significantly expanded by improving the mechanical properties of widely accepted Ti-6Al-4V alloys without changing the alloy composition or biocompatibility thereof. Thus, there is no need to generate these substantial costs associated with clinical testing of new implantable alloys.

Similar advantages are seen in other applications. Creep resistance is an important feature in many technical applications. While it is known that increasing the oxygen content improves the creep resistance of Ti-6Al-4V alloys, an increase in oxygen content still greatly reduces fatigue strength. These limitations can be overcome by increasing the oxygen content and refining the microstructure via thermal hydrogen treatment.

The increase in creep in Ti-6Al-4V alloys can be improved by using alloys developed specifically for creep resistance properties (e.g., Ti-6Al2Sn4Zr2 Mo-Si). The specification for this alloy limits the oxygen content to 1500 ppm. Generally, increasing the oxygen content above this maximum embrittles the alloy, but the refined microstructure provided by the hot hydrogen treatment more than offsets this embrittlement to provide improved creep resistance, while providing good fatigue resistance and durability.

Another application that would benefit from the present invention is ultrasound. Titanium is a preferred material for ultrasonic horns (ultrasonic horns) or other components used in ultrasonic transmissions. However, ultrasonic systems are designed and tuned around very specific alloy compositions, and changing the alloy can affect the ultrasonic performance of the system or device. Unlike the orthopedic industry, however, the ultrasonic industry developed its design around Ti-6Al-4V alloys. Fatigue performance can be a consideration due to the high vibration frequencies seen in ultrasound applications. Refining the microstructure while increasing the oxygen content can provide improved strength and fatigue properties to the titanium component without negatively impacting the ultrasonic properties of the titanium component.

Consideration of temperature uniformity:

the thermal hydrogen treatment process has been known for some time and a great deal of research has been carried out on the process, demonstrating that the thermal hydrogen treatment process can be used to improve mechanical properties by refining the microstructure.

However, despite previous efforts, thermal hydrogen treatment has never been successfully commercialized. While this may be due to a number of factors, such as industry reluctance to use hydrogen, the limitation of the cross-section that can be successfully processed, difficulties in controlling oxygen or other sources of contamination during processing, or the cost and complexity of additional processing steps, we believe that the fundamental problem of temperature furnace atmosphere uniformity has not been addressed in previous work.

The hot hydrogen process is effective over a fairly wide temperature range, depending on the alloy being treated. Such as the temperatures and ranges discussed herein. Since thermal hydrogen treatment processes are effective over a wide range, the importance of accurate temperature uniformity and control is ignored. Creating a uniform temperature environment in an atmospheric furnace (as opposed to a high vacuum) is very challenging. Due to the exothermic nature of the hydrogenation process, thermal hydrogen treatment presents more challenges than other thermal treatment processes that do not exhibit an exothermic phenomenon during the thermal cycle.

In fact, in such environments, the control instrumentation may not accurately reflect the temperature of the product, or the temperature uniformity throughout the processing environment. This means in practice that the components are subjected to different temperatures in the furnace and, therefore, have different mechanical properties. This is a subtle statement because each location and corresponding condition within the furnace will yield sufficient mechanical properties at the start of the test, but the resulting composite process is quite different due to environmental variations, and statistical analysis will show that a furnace environment with too large a temperature range will not consistently provide an acceptable product.

This problem can be overcome by taking careful measures to reduce temperature variations within the furnace. While this process is "effective" over many temperature ranges, it is not "effective" over all temperature ranges simultaneously. In short, it has been found that the more uniform the environment of the furnace, the more consistent the final product. This seems to be self-evident, since reducing the variations is usually the core principle of quality control, however, aspects of this type of processing, such as the convective nature of the exothermic and heat-treatment atmospheres associated with hydrogenation, in which large amounts of gas are absorbed by the article, particularly aggravating the temperature variations in the heating environment, necessitate additional measures to reduce the temperature variations.

It is normal to see a temperature change of 100 c in a furnace. While most furnaces can be easily controlled to a set temperature by closed loop feedback control, this only addresses the area immediately adjacent to the control temperature sensor. This is a challenge in many types of furnaces, including those that process at, below, or above ambient pressure.

As previously mentioned, the hot hydrogen process becomes more difficult to control due to the exotherm associated with hydrogen absorption by the titanium article. This release of heat must be addressed by the design of the furnace. In addition, if the furnace is not operated under a high vacuum, natural convection within the furnace will create a large temperature gradient throughout the furnace. Also, these problems must be solved by the design of the furnace. Some approaches to addressing this difficulty include adding fans within the furnace to force gas circulation and/or configuring the interior of the furnace to accommodate uniform distribution of forced gas.

By careful design of the furnace and thermal profile, temperature uniformity can be greatly improved and the uniformity of the components throughout the furnace can be improved to the extent necessary to demonstrate run-to-run uniformity and predictability.

In some embodiments of the invention, these features are considered and implemented. Careful development and modification of these furnace conditions indicate that +/-14 ℃ uniformity helps to narrow the performance variation during the production of the hydrogenated beta phase, while +/-10 ℃ or less uniformity is preferred. Furthermore, in the dehydrogenation step, uniformity of +/-10 ℃ helps to narrow the difference in properties, and uniformity of +/-3 ℃ or less is preferable. Pyrometry is a common industrial problem and has its standard of practice. Aerospace Material specifications (Aerospace Materials Specification)2750E, "pyrometry" specifies different temperature uniformity levels, ranging from +/-28 ℃ to +/-3 ℃, including 14 ℃, 10 ℃, 8 ℃ and 6 ℃. Of course, other temperature uniformity set points may be selected, for example, within a preferred range of +/-14 ℃ or +/-10 ℃.

In practice, the two most critical parts of the cycle are the production of the hydrogenated beta phase by maintaining the components above the hydrogen inhibiting transition temperature, and the removal of hydrogen by vacuum. Both of these situations are typically performed during the dwell period rather than during the ramp period, and the discussion of uniformity focuses primarily on uniformity during these dwell periods. While temperature control is always an important factor in thermal processing, the initial hydrogenation step and eutectoid transformation step are not as sensitive to temperature variations.

It will be appreciated that during the exothermic process, the temperature of the furnace may rise slightly; the importance of the present invention is that during these processes, uniformity throughout the furnace is maintained.

The improved process includes processing a titanium article by introducing hydrogen to the titanium article to reduce the beta transus temperature. The article is then heated above the reduced beta transus temperature to form the hydrogenated beta phase while maintaining furnace temperature uniformity at +/-14 ℃ or more preferably +/-10 ℃ or less. After that, the temperature is lowered below the eutectoid transition point to affect the eutectoid transition. After this, the article is heated (dehydrogenated) in vacuum to remove hydrogen, thereby obtaining a worked article. The dehydrogenation is preferably carried out at +/-14 ℃ or less, or more preferably +/-10 ℃ or less. By "or below" it is understood that these temperature variations may fall within the ranges specified, or may fall within ranges less than these ranges. For example, a range of +/-10 ℃ or less would include the following ranges: +/-9 ℃ or below, +/-8 ℃ or below, +/-7 ℃ or below and the like.

An improved process includes processing a titanium alloy having an oxygen content greater than 2000ppm by introducing hydrogen into the article to reduce the beta transus temperature. The article is then heated above the beta transus temperature to form a hydrogenated beta phase while maintaining furnace temperature uniformity at +/-14 ℃, or more preferably +/-10 ℃ or less. Then, the temperature is lowered below the eutectoid transition point. Then, the article is heated in vacuum, thereby obtaining a processed article. The hydrogenation is preferably carried out at +/-14 ℃ or more preferably at +/-10 ℃ or less.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

The invention has industrial applicability in the field of metallurgy.