阅读说明：本技术 一种增材制造金属材料中裂纹的消除方法 (Method for eliminating cracks in additive manufacturing metal material ) 是由 胡小刚 朱强 于 2020-12-30 设计创作，主要内容包括：本发明涉及一种增材制造金属材料中裂纹的消除方法,所述消除方法包括如下步骤：将含裂纹的增材制造金属材料进行加热并保温,之后在所述保温温度下进行等静压处理,降温得到裂纹消除的增材制造金属材料。本发明提供的消除方法,采用微量重熔的方法形成晶间液膜,将裂纹回填形成固液两相共存的状态,然后控制再凝固速率,实现材料均匀凝固收缩,过程中可施加等静压力,抑制缩孔的产生,最终实现裂纹的愈合及构件致密化,同时还可以提高构件的综合力学性能。(The invention relates to a method for eliminating cracks in an additive manufacturing metal material, which comprises the following steps: and heating and insulating the additive manufacturing metal material containing the cracks, then carrying out isostatic pressing treatment at the insulation temperature, and cooling to obtain the additive manufacturing metal material with the cracks eliminated. The elimination method provided by the invention adopts a micro remelting method to form an intercrystalline liquid film, backfills cracks to form a state of coexistence of solid and liquid phases, then controls the re-solidification rate, realizes uniform solidification and shrinkage of materials, can apply isostatic pressure in the process, inhibits the generation of shrinkage cavity, finally realizes the healing of the cracks and the densification of the component, and can also improve the comprehensive mechanical property of the component.)

1. A method of eliminating cracks in an additive manufactured metallic material, the method comprising the steps of: heating and insulating the additive manufacturing metal material containing the cracks, then carrying out isostatic pressing treatment at the insulation temperature, and cooling to obtain the additive manufacturing metal material with the cracks eliminated; the pressure of the isostatic pressing treatment is less than or equal to 10 MPa.

2. The abatement method of claim 1, wherein the additive manufacturing metal material comprises 1 of a nickel-based alloy, a cobalt-based alloy, an aluminum-based alloy, an iron-based alloy, a titanium-based alloy, and a copper-based alloy.

3. The elimination method according to claim 1 or 2, characterized in that the end temperature of the heating is 5 to 60 ℃ above the solidus temperature of the alloy at the temperature of the metallic material.

4. Elimination process according to any one of claims 1 to 3, wherein the heating is carried out at a heating rate of 10 to 100 ℃/min, preferably 10 to 30 ℃/min.

5. The elimination method of any one of claims 1 to 4, wherein the incubation temperature of the incubation is an end point temperature of the heating;

preferably, the time for heat preservation is 5-60 min.

6. An abatement method according to any of claims 1 to 5, wherein the rate of pressure increase in the isostatic pressure treatment is in the range of 1 to 5MPa/min, preferably 2 to 3 MPa/min.

7. An elimination method according to any one of claims 1 to 6, characterized in that the cooling rate of the cooling is 1-10 ℃/min, preferably 1-3 ℃/min.

8. The elimination method according to any one of claims 1 to 7, wherein the end temperature of said temperature reduction is 20 to 30 ℃ below the solidus temperature of the metal material after the isostatic pressing treatment.

9. The abatement method of any one of claims 1-8, wherein the furnace cooling is performed after the temperature reduction reaches the endpoint temperature.

10. An elimination method according to any one of claims 1 to 9, characterized in that it comprises the steps of: heating and insulating the additive manufacturing metal material containing the cracks, then carrying out isostatic pressing treatment at the insulation temperature, and cooling to obtain the additive manufacturing metal material with the cracks eliminated;

the heating end point temperature is that the temperature of the metal material is 5-60 ℃ above the solidus temperature of the alloy, and the heating rate is 10-100 ℃/min;

the heat preservation temperature is the heating end point temperature, and the heat preservation time is 5-60 min;

the pressure of the isostatic pressing treatment is less than or equal to 10MPa, and the pressurization rate in the isostatic pressing treatment is 1-5 MPa/min;

the cooling rate of the cooling is 1-10 ℃/min, and the end point temperature of the cooling is 20-30 ℃ below the solidus temperature of the metal material after isostatic pressing treatment.

Technical Field

The invention relates to the field of defect elimination, in particular to a method for eliminating cracks in an additive manufacturing metal material.

Background

At present, the additive manufacturing technology is a digital manufacturing technology for realizing the dieless forming of a component by adding and stacking materials layer by layer. The method organically integrates material preparation/precise forming, and manufactures and disperses the three-dimensional complex-shaped parts into simple two-dimensional plane shapes to be stacked layer by layer, overcomes the limitation that the traditional process is difficult to machine or can not machine, and can realize free manufacturing in the true sense. The metal laser additive manufacturing technology integrates the advantages of low cost, short flow, high performance, shape control/controllability and the like, can provide a brand new and effective solution for the preparation of metal components which are difficult to process in the traditional process, and has very wide application prospect in the field of high-value-added metal components such as aerospace, major weaponry, automobiles and the like.

The cracks are one of main failure modes of the laser additive manufacturing component, and are main factors which restrict the application of high-performance metals, particularly alloy laser additive manufacturing technology with high crack sensitivity. The crack form generated in the laser additive manufacturing process mainly comprises a solidification crack and a liquefaction crack, wherein the solidification crack is mainly caused by pulling apart an intercrystalline liquid film by thermal stress at the later stage of molten pool solidification; the liquefaction cracks are mainly formed by that a low-melting-point eutectic phase among crystals in a heat affected zone is remelted to form a liquid film under the action of solidification heat and then is torn under the action of thermal stress. Based on the analysis of the form and formation mechanism of the printing crack, two necessary conditions for crack generation in laser additive manufacturing are known: liquefying the low-melting-point phase in the later solidification period or the heat affected zone so as to form a continuous or semi-continuous liquid film on the position of the grain boundary; there is a sufficiently large tensile stress in the vicinity of the liquid film.

At present, the control method for printing cracks at home and abroad mostly focuses on two factors of online regulation and control. CN110918992A discloses a high-temperature alloy additive manufacturing method, which is characterized in that the proportion range of element components such as C, B and the like in alloy powder is controlled to eliminate the cracking tendency in the high-temperature alloy additive manufacturing process and eliminate the microcracks in a workpiece; however, the method of improving the hot cracking sensitivity of the alloy by adjusting the components will change the components of the alloy, and further influence the performance of the alloy, so that only part of the alloy system is suitable for the method.

CN206028732U discloses a metal vibration material disk powder bed preheating device, adopts microwave to preheat the metal powder bed, has solved the limited problem of current vibration material disk equipment heating temperature, reduces the temperature gradient in the shaping process through improving the powder bed preheating temperature, and then reduces thermal stress in order to improve the alloy fracture tendency.

CN208513642U discloses a laser additive manufacturing device with preheating function and slow cooling function, which can effectively reduce the temperature gradient in the cladding process, reduce the thermal stress, and inhibit the generation of crack defects. However, this method will greatly increase the cost of the printing equipment, and the space for preheating the substrate is limited, so it is suitable for smaller size printed products.

The research methods are all that the solidification behavior of the alloy is regulated and controlled on line in the printing process or the base material is preheated to reduce the thermal stress, so that the generation of cracks is inhibited. There have also been studies showing that post-treatment of a printed article having microcracks can also effectively eliminate print cracks. CN105562694A discloses a hot isostatic pressing three-control method suitable for additive manufacturing parts, aiming at different printing part materials and defect conditions, heat preservation is carried out for 2-4 hours in a high-temperature region lower than the alloy solidus temperature, static pressure of 120-200MPa is applied in the treatment process, the shape and size precision of the additive manufacturing parts are ensured, proper phase and structure are obtained, and the part performance is improved. The hot isostatic pressing technology is an effective measure for eliminating defects such as holes and cracks in the metal component, but the technology has high process cost and cannot heal the holes and cracks on the surface of the component.

CN108994304A discloses a method for eliminating metal material additive manufacturing cracks and improving mechanical properties, which adopts a discharge plasma sintering technology to heat a metal additive manufacturing block to 0.8-0.9 times of recrystallization temperature, and simultaneously adopts a mechanical pressurization method to apply 30-50MPa pressure to realize printing crack healing. The technical principle is similar to hot isostatic pressing, namely crack healing is realized by applying pressure to a metal solid high-temperature area, however, the method needs to compact the block by mechanically pressurizing the mould, so that only regular structures such as blocks or cylinders can be processed, printed products with complex structures cannot be processed, and the method can be used for manufacturing components with complex shapes, which is the core advantage of the additive manufacturing technology.

Disclosure of Invention

In view of the problems in the prior art, the invention aims to provide a method for eliminating cracks in an additive manufacturing metal material, which comprises the steps of remelting the area near the cracks in a trace manner, backfilling the cracks by solid-liquid phase change volume expansion, completely eliminating the original printing thermal cracks by controlling the re-solidification process, and simultaneously improving the comprehensive mechanical properties of a component.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for eliminating cracks in an additive manufacturing metal material, which comprises the following steps: heating and insulating the additive manufacturing metal material containing the cracks, then carrying out isostatic pressing treatment at the insulation temperature, and cooling to obtain the additive manufacturing metal material with the cracks eliminated; the pressure of the isostatic pressing treatment is less than or equal to 10 MPa.

The elimination method provided by the invention adopts a micro remelting method to form an intercrystalline liquid film, backfills cracks to form a state of coexistence of solid and liquid phases, then controls the re-solidification rate, realizes uniform solidification and shrinkage of materials, can apply isostatic pressure in the process, inhibits the generation of shrinkage cavity, finally realizes the healing of the cracks and the densification of the component, and can also improve the comprehensive mechanical property of the component. This is because the position where the crack is generated is the position of the grain boundary where the molten pool is finally solidified, regardless of whether the liquid film is torn by the thermal stress at the final stage of solidification or the low-melting-point phase is torn by the thermal stress after the second melting in the heat affected zone. By adopting a micro remelting method, the grain boundary is remelted a little, the generated liquid volume expands and backfills cracks to realize crack healing due to solid-liquid phase transformation, and then the solidification rate, namely the cooling rate, is controlled to regulate the thermal stress of the re-solidification and realize uniform shrinkage of the component, so that the cracks are prevented from being generated again. Applying a certain isostatic pressure in the secondary solidification process, and inhibiting the generation of shrinkage cavity by uniform elastic deformation

In the present invention, the pressure of the isostatic pressing treatment is 10MPa or less, and may be, for example, 10MPa, 9MPa, 8MPa, 7MPa, 6MPa, 5MPa, 4MPa, 3MPa, 2MPa, 1MPa or 0MPa, but is not limited to the values listed above, and other values not listed in the range are also applicable.

In the invention, when the pressure of the hot isostatic pressing treatment is 0MPa, the temperature is directly reduced after the heat preservation treatment in the process.

As a preferred technical scheme of the invention, the additive manufacturing metal material comprises 1 of nickel-based alloy, cobalt-based alloy, aluminum-based alloy, iron-based alloy, titanium-based alloy and copper-based alloy.

In a preferred embodiment of the present invention, the end point temperature of the heating is 5 to 60 ℃ higher than the solidus temperature of the alloy, and may be, for example, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃ or 60 ℃, but is not limited to the above-mentioned values, and other values not shown in the above range are also applicable.

As a preferred embodiment of the present invention, the heating rate is 10 to 100 ℃/min, for example, 10 ℃/min, 20 ℃/min, 30 ℃/min, 40 ℃/min, 50 ℃/min, 60 ℃/min, 70 ℃/min, 80 ℃/min, 90 ℃/min or 100 ℃/min, but not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable, and preferably 10 to 30 ℃/min.

As a preferable technical solution of the present invention, the heat-retaining temperature of the heat retention is the end point temperature of the heating.

Preferably, the time for the heat preservation is 5 to 60min, for example, 5min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min, etc., but is not limited to the enumerated values, and other values not enumerated in this range are also applicable.

In a preferred embodiment of the present invention, the pressure increase rate in the isostatic pressing treatment is 1 to 5MPa/min, and may be, for example, 1MPa/min, 1.5MPa/min, 2MPa/min, 2.5MPa/min, 3MPa/min, 3.5MPa/min, 4MPa/min, 4.5MPa/min, or 5MPa/min, but is not limited to the above-mentioned values, and other values not listed in this range are also applicable, and preferably 2 to 3 MPa/min.

As a preferred embodiment of the present invention, the cooling rate of the cooling is 1 to 10 ℃/min, and for example, 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, or 10 ℃/min, etc., but not limited to the above-mentioned values, and other values not listed in the above range are also applicable, and preferably 1 to 3 ℃/min.

In a preferred embodiment of the present invention, the final temperature of the reduction is 20 to 30 ℃ below the solidus temperature of the metal material after the isostatic pressing, and may be, for example, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃ or 30 ℃, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

As the preferable technical scheme of the invention, the furnace cooling is carried out after the temperature reduction reaches the end point temperature.

As a preferred technical solution of the present invention, the elimination method includes the steps of: heating and insulating the additive manufacturing metal material containing the cracks, then carrying out isostatic pressing treatment at the insulation temperature, and cooling to obtain the additive manufacturing metal material with the cracks eliminated;

the heating end point temperature is that the temperature of the metal material is 5-60 ℃ above the solidus temperature of the alloy, and the heating rate is 10-100 ℃/min;

the heat preservation temperature is the heating end point temperature, and the heat preservation time is 5-60 min;

the pressure of the isostatic pressing treatment is less than or equal to 10MPa, and the pressurization rate in the isostatic pressing treatment is 1-5 MPa/min;

the cooling rate of the cooling is 1-10 ℃/min, and the end point temperature of the cooling is 20-30 ℃ below the solidus temperature of the metal material after isostatic pressing treatment.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) the elimination method provided by the invention adopts a micro remelting method to form an intercrystalline liquid film, backfills cracks to form a state of coexistence of solid and liquid phases, realizes uniform solidification and shrinkage of materials by controlling the re-solidification rate, simultaneously applies isostatic pressure in the process, inhibits the generation of shrinkage cavities, finally realizes the healing of the cracks and the densification of the additive manufacturing component, and simultaneously improves the comprehensive mechanical property of the additive manufacturing component.

(2) By the elimination method provided by the invention, the porosity of the additive manufacturing metal material with cracks is reduced to be below 0.0009% after the additive manufacturing metal material is processed, and the tensile strength and the elongation of the processed metal material are obviously improved.

Drawings

FIG. 1 is a schematic view of the microstructure of a sample of an additive manufactured metallic material used in the present invention;

FIG. 2 is a graph comparing the density of samples before and after treatment in example 1 of the present invention;

FIG. 3 is a schematic view showing the distribution of internal defects before and after the treatment of a sample in example 1 of the present invention;

FIG. 4 is a graph comparing density before and after sample treatment in example 2 of the present invention;

FIG. 5 is a schematic diagram showing the distribution of internal defects before and after the treatment of a sample in example 2 of the present invention.

The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

Detailed Description

To better illustrate the invention and to facilitate the understanding of the technical solutions thereof, typical but non-limiting examples of the invention are as follows:

the additive metal material is obtained by the following method:

the material IN738LC is selected as spherical powder of precipitation-strengthened superalloy, D10 is 20.5 μm, D50 is 30.8 μm, and D90 is 40 μm. Preparing an IN738LC alloy block by adopting a selective laser melting process, wherein the selective laser melting process parameters are as follows: the laser power is 250w, the scanning speed is 1000mm/s, the scanning distance is 90 mu m, and the layering thickness is 30 mu m;

analyzing the microstructure of a printed part after the part is formed, wherein the result is shown in figure 1, which shows that the printing defect exists in the form of cracks under the process;

③ 1 each of the test sample A (15 mm. 15mm cube), the test sample B (3 mm. 3mm cube), the test sample C (15 mm. 15mm cube) and the test sample D (3 mm. 3mm cube) was prepared; and a tensile sample for mechanical property testing;

fourthly, testing the density value of the sample A by adopting an Archimedes density testing method, and calculating the relative density of the block body to be 99.15%; analyzing the internal defects of the sample B by adopting an x-CT testing technology, and measuring that the crack volume ratio is 0.826%; testing the density value of the sample C by adopting an Archimedes density testing method, and calculating the density of the sample C to be 99.09%; analyzing the internal defect space distribution of the sample D by adopting an x-CT testing technology, and measuring that the crack volume ratio is 0.889%;

example 1

The embodiment provides a method for eliminating cracks in an additive manufacturing metal material, wherein samples A and B are processed;

placing a sample A, B into a heat treatment furnace, vacuumizing the furnace body, introducing high-purity argon to inhibit the oxidation of the sample, heating the sample to 1285 ℃ along with the furnace, keeping the temperature for 5min after the temperature is raised to a target temperature, cooling to 1200 ℃ at the speed of 2 ℃/min, namely the pressure of hot isostatic pressing treatment is 0MPa, cooling to room temperature along with the furnace, and taking out the sample;

the density value of the sample A (after treatment) is tested by an Archimedes density test method, and the density is improved to 99.86 percent. Figure 2 compares the density of sample a before and after treatment.

The porosity reduction was 0.144% when sample B (after treatment) was analyzed for internal defect space using x-CT testing techniques. FIG. 3 compares the internal defect distribution before and after sample B treatment in situ.

Tensile properties were tested on the product before and after treatment, with the specimen dimensions and test methods following the ASTM E8 standard. The test results showed that untreated IN738LC had a tensile strength of 400MPa at 850 ℃ and an elongation of 4.5%, and after the elimination treatment, it had a tensile strength of 770MPa and an elongation of 6.7%.

Example 2

The embodiment provides a method for eliminating cracks in an additive manufacturing metal material, and samples C and D are processed;

and placing the samples C and D into a heat treatment furnace, vacuumizing the furnace body, introducing high-purity argon to inhibit the oxidation of the samples, heating the samples to 1285 ℃ along with the furnace, wherein the heating rate is 10 ℃/min, keeping the temperature at the target temperature for 5min, and then starting to pressurize the furnace body by air pressure, the isostatic pressure is 7MPa, and the pressurizing rate is 2.5 MPa/min. Then keeping the pressure constant, cooling to 1200 ℃ at the speed of 2 ℃/min, then cooling to room temperature along with the furnace, releasing the pressure, and taking out a sample;

the density value of the sample C (after treatment) is tested by an Archimedes density test method, and the density is improved to 99.99 percent. Fig. 4 compares the density of sample C before and after treatment.

The porosity reduction was 0.0009% when sample D (after treatment) was analyzed for internal defect space using x-CT testing techniques. FIG. 5 compares the internal defect distribution before and after sample D treatment in situ.

Tensile properties were tested on the product before and after treatment, with the specimen dimensions and test methods following the ASTM E8 standard. The test results showed that untreated IN738LC had a tensile strength of 400MPa at 850 ℃ and an elongation of 4.5%, and after the elimination treatment, it had a tensile strength of 860MPa and an elongation of 9.8%.

From the results of the above examples, it can be known that the elimination of cracks in the metal material manufactured by the additive is realized by controlling the temperature rising speed and the temperature lowering speed in a reasonable temperature range, and the elimination of cracks can be further strengthened by further hot isostatic pressing treatment, and the tensile strength and the elongation are further improved.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.