阅读说明：本技术 一种钛合金表面渗氮工艺 (Titanium alloy surface nitriding process ) 是由 冯志浩 孙信阳 秦雪明 孟致安 胡希磊 韩鹏彪 于 2019-10-16 设计创作，主要内容包括：本发明具体公开一种钛合金表面渗氮工艺。所述方法包括：表面经过预处理的钛合金基体放入真空渗氮装置中,抽真空,将所述真空渗氮装置升温至渗氮温度；所述渗氮温度为400-1300℃；向所述真空渗氮装置内通入氮化气体,氮化0.1-15h,通入惰性气体,冷却至室温,即可在钛合金表面形成氮化钛层；所述氮化气体为体积比为1:0-5的氮气和氩气。本发明所提供的钛合金表面渗氮工艺,可根据钛合金服役的具体要求,在低温和高温下制备不同性能的改性钛合金,其中,氮化钛层的厚度可达到20-200μm,硬度最高可达到2100HV<Sub>0.5</Sub>,平均磨损失重为1.67-3.14g,相比基体硬度和耐磨性明显提高。(The invention specifically discloses a titanium alloy surface nitriding process. The method comprises the following steps: putting the titanium alloy matrix with the surface subjected to pretreatment into a vacuum nitriding device, vacuumizing, and heating the vacuum nitriding device to a nitriding temperature; the nitriding temperature is 400-1300 ℃; introducing nitriding gas into the vacuum nitriding device, nitriding for 0.1-15h, introducing inert gas, and cooling to room temperature to form a titanium nitride layer on the surface of the titanium alloy; the nitriding gas is nitrogen and argon in a volume ratio of 1: 0-5. The surface nitriding process of the titanium alloy can prepare modified titanium alloys with different properties at low temperature and high temperature according to the specific requirements of the service of the titanium alloy, wherein the thickness of the titanium nitride layer can reach 20-200 mu m, and the highest hardness can reach 2100HV 0.5 The average abrasion weight loss is 1.67-3.14g, and compared with the matrix hardness and the abrasion resistance, the matrix hardness and the abrasion resistance are obviously improved.)

1. a surface nitriding process for titanium alloy is characterized by comprising the following steps:

Step a, putting a titanium alloy matrix with a pretreated surface into a vacuum nitriding device, vacuumizing, and heating the vacuum nitriding device to a nitriding temperature; the nitriding temperature is 400-1300 ℃;

And b, introducing nitriding gas into the vacuum nitriding device, nitriding for 0.1-15h, introducing inert gas, and cooling to room temperature to form a titanium nitride layer on the surface of the titanium alloy.

2. The process for surface nitriding of titanium alloys according to claim 1, wherein in step a the nitriding temperature is 400-900 ℃.

3. the process for surface nitriding of titanium alloys according to claim 2, wherein in step b, the nitriding gas is a mixed gas of nitrogen and argon in a volume ratio of 1: 0-1.

4. A process for surface nitriding of titanium alloys according to claim 3, wherein in step b the nitriding time is 3-15 h.

5. The process for surface nitriding of titanium alloys according to claim 1, wherein in step a, the nitriding temperature is 900-1300 ℃.

6. the process for surface nitriding of titanium alloys according to claim 5, wherein in step b, the nitriding gas is a mixed gas of nitrogen and argon in a volume ratio of 1: 1-5.

7. a process for surface nitriding of titanium alloys according to claim 6, wherein in step b the nitriding time is 0.1-3 h.

8. A titanium alloy surface nitriding process according to any one of claims 1-7, wherein in step a, the temperature is raised to the nitriding temperature by means of programmed temperature raising at a rate of 1-10 ℃/min; and/or

And step b, cooling to room temperature in a programmed cooling mode, wherein the cooling rate is 0.5-3 ℃/min.

9. the process for surface nitriding of titanium alloys according to claim 1, wherein in step b, the nitriding gas is introduced at a rate of 1-10L/min.

10. The process for surface nitriding of titanium alloys according to claim 9, wherein in step a, vacuum is applied to a vacuum degree of 0.1Pa or less; and/or

In the step a, the surface pretreatment method of the titanium alloy substrate comprises the following steps: and (3) sequentially grinding the titanium alloy substrate by using 100-mesh, 200-mesh and 500-mesh water-grinding abrasive paper, then ultrasonically cleaning for 20-30min under the condition of power of 30-50Hz, and drying by cold air.

Technical Field

The invention relates to the technical field of titanium alloy surface modification, in particular to a titanium alloy surface nitriding process.

Background

Compared with other metal materials, the titanium alloy has the advantages of low density, high specific strength, corrosion resistance, low temperature resistance and high temperature resistance, and is widely applied to the fields of military industry, nuclear industry, chemical industry, automobile industry and the like. However, the titanium alloy has a low surface hardness, a poor wear resistance, and a high sensitivity to adhesive wear and fretting wear, and thus its range of use is greatly limited. How to improve the hardness and wear resistance of titanium alloys has become one of the hot spots in the field of titanium alloys.

the titanium nitride has the advantages of high melting point, high hardness, excellent wear resistance, excellent high-temperature stability and the like. The preparation of the titanium nitride modified layer on the surface of the titanium alloy is an effective measure for improving the surface hardness, improving the wear resistance, prolonging the service life and expanding the application range of the titanium alloy. At present, a titanium nitride modified layer is prepared on the surface of a titanium alloy by mainly adopting magnetron sputtering, ion nitriding, laser gas nitriding and gas nitriding methods. An obvious interface exists between the film layer and the substrate treated by the magnetron sputtering method, the bonding strength is poor, and the coating is thin; ion nitriding cannot process parts with complex shapes, and the cost is high; laser nitriding is prone to structural defects (e.g., porosity, etc.) and cracks. The gas nitriding is simple and easy to implement, has low cost, can form nitride hard phase on the surface of the titanium alloy, and obviously improves the wear resistance and the corrosion resistance, thereby being widely applied. However, the existing gas nitriding is generally carried out at low temperature, and has the defects of slow nitriding speed, thin permeated layer, brittle permeated layer, overlong treatment time and the like, the prepared modified titanium alloy can not meet the requirement of long-term service of industrial production,

Disclosure of Invention

Aiming at the problems that nitriding is generally carried out at low temperature in the prior art, and the defects of low nitriding speed, thin diffusion layer, brittle diffusion layer, overlong processing time and the like exist, the invention provides a titanium alloy surface nitriding process.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

A surface nitriding process for titanium alloy specifically comprises the following steps:

Step a, putting a titanium alloy matrix with a pretreated surface into a vacuum nitriding device, vacuumizing, and heating the vacuum nitriding device to a nitriding temperature; the nitriding temperature is 400-1300 ℃;

And b, introducing nitriding gas into the vacuum nitriding device, nitriding for 0.1-15h, introducing inert gas, and cooling to room temperature to form a titanium nitride layer on the surface of the titanium alloy.

Compared with the prior art, the modified titanium alloy with different properties can be prepared at low temperature and high temperature according to the specific requirements of the service of the titanium alloy, and the problems of rough surface, cracks, uneven tissue and the like of the modified titanium alloy prepared by the existing preparation process are solved. The thickness of the titanium nitride layer of the modified titanium alloy prepared by the nitriding process provided by the invention can reach 20-200 mu m, and the highest hardness can reach 2100HV_0.5The average abrasion weight loss is 1.67-3.14g, the friction coefficient is 0.15-0.36, compared with the matrix hardness and the abrasion resistance, the prepared titanium nitride layer has the advantages of fine and uniform crystal grains, flat and crack-free surface, simple process, strong controllability and wide application prospect.

Preferably, in the step a, the nitriding temperature is 400-900 ℃.

preferably, when the nitriding temperature is 400-900 ℃, in the step b, the nitriding gas is a mixed gas of nitrogen and argon in a volume ratio of 1: 0-1.

Preferably, when the nitriding temperature is 400-900 ℃, in the step b, the nitriding time is 3-15 h.

Nitriding is carried out at the low temperature of 400-900 ℃, and mixed gas of nitrogen and argon with the volume ratio of 1:0-1 is adopted, so that nitrogen atoms can be uniformly diffused in matrix tissues, the flatness of a nitriding layer can be improved, the nitriding layer does not have defects such as pits and bulges, and the wear resistance and hardness of the nitrogen carbide layer are improved.

preferably, in the step a, the nitriding temperature is 900-1300 ℃.

preferably, in the step b, the nitriding gas is a mixed gas of nitrogen and argon in a volume ratio of 1: 1-5.

the nitriding temperature is an important factor influencing the diffusion rate of nitrogen atoms, and the higher the temperature is, the higher the diffusion speed is, and the larger the thickness of a diffusion layer is. However, at higher temperatures (above 950 ℃), the nitride layer increases in thickness, and due to the difference in the coefficients of expansion between the nitride layer and the substrate, the nitride layer can generate a large stress on the substrate during the nitriding process of the titanium alloy, so that the film layer cracks, and the cracked and exposed substrate continues to react with nitrogen, so that the surface layer structure becomes loose. Thus, the prior art generally chooses nitriding at temperatures up to 850-950 ℃.

According to the invention, the nitrogen-argon ratio is controlled within the range of 1:1-5, and the content of nitrogen in the mixed gas is controlled, so that the nitrogen absorption speed and the diffusion rate of nitrogen atoms in a matrix are controlled, the nitriding is smoothly realized at the temperature of above 900-1300 ℃ phase transition point, and the problems of large and thick grains, uneven structure, cracks and the like of a nitrided layer, which are easily caused in the high-temperature nitriding, are avoided. When the nitrogen-argon ratio exceeds 1:1, high-density nitride is concentratedly distributed on the surface layer, so that the elastic modulus of titanium nitride prepared on the surface layer is increased, the brittleness is increased, and defects such as cracks are generated.

preferably, in step b, the nitriding time is 0.1-3 h.

The longer the nitriding time, the larger the thickness of the carburized layer. But when the nitriding time reaches a certain value, the speed of increasing the thickness of the infiltrated layer is reduced, but the tissue defects are increased, and the optimal high-temperature nitriding time can effectively reduce the tissue defects on the premise of ensuring the thickness of the infiltrated layer.

Preferably, in the step a, the temperature is raised to the nitriding temperature by adopting a temperature programming mode, and the temperature raising rate is 1-10 ℃/min.

the preferred rate of temperature increase may result in a more uniform titanium alloy structure.

preferably, in the step b, the temperature is reduced to room temperature in a programmed cooling mode, and the cooling rate is 0.5-3 ℃/min.

The preferable cooling rate can avoid the problem that the nitride layer and the matrix structure are too stressed to fall off.

Preferably, in step b, the introduction rate of the nitriding gas is 1-10L/min.

the preferred introduction rate of the nitriding gas is beneficial to increasing the nitrogen content of each thickness part in the nitrided layer, thereby improving the strength of the whole carburized surface.

Alternatively, the inert gas in step b may be an inert gas conventional in the art, such as argon, helium, and the like. The inert gas is continuously introduced from the end of nitriding until the nitrided sample is cooled to room temperature

Preferably, in step a, vacuum is applied until the vacuum degree is less than 0.1 Pa.

Before nitriding, the device is vacuumized until the vacuum degree is lower than 0.1Pa, so that other gases and impurities adsorbed on the surface of the titanium alloy substrate can be desorbed and discharged out of the nitriding device, the surface of the titanium alloy can be further purified, the absorption and diffusion of nitrogen atoms in the nitriding process can be promoted, and the nitriding efficiency can be improved; meanwhile, the harmful atmosphere in the nitriding device can be reduced, other gases are effectively prevented from forming an adsorption layer on the surface of the titanium alloy substrate, and oxidation, hydrogen embrittlement and black tissues are prevented from being generated.

Preferably, in the step a, the surface of the titanium alloy substrate is pretreated by the following method: and (3) sequentially grinding the titanium alloy substrate by using 100-mesh, 200-mesh and 500-mesh water-grinding abrasive paper, then ultrasonically cleaning for 20-30min under the condition of power of 30-50Hz, and drying by cold air.

The optimal pretreatment method for the titanium alloy surface can effectively remove impurities adsorbed on the surface and reduce the generation of the defects of the nitriding layer.

the nitrogen and the argon are high-purity gases with the purity of more than or equal to 99.99 percent. The titanium alloy substrate may be a titanium alloy conventional in the art, such as a Ti-6Al-4V, TB6, TC4, or TA15 titanium alloy, and the like. The nitriding apparatus may be a vacuum furnace or an atmosphere tube furnace.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a cross-sectional view of a titanium nitride layer on the surface of a titanium alloy prepared in example 1 of the present invention;

FIG. 2 is a cross-sectional view of a titanium nitride layer on the surface of a titanium alloy prepared in example 2 of the present invention;

FIG. 3 is a cross-sectional view of a titanium nitride layer on the surface of a titanium alloy prepared in example 3 of the present invention;

Fig. 4 is a graph showing hardness distribution of the titanium nitride layer on the surface of the titanium alloy in examples 1 to 3 of the present invention.

fig. 5 is a bar graph of the wear loss of the titanium nitride layer and the titanium alloy matrix prepared in examples 1 to 3 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to better illustrate the invention, the following examples are given by way of further illustration.