阅读说明：本技术 一种钛合金部件深腔螺纹局部离子渗氮的方法 (Local ion nitriding method for deep cavity threads of titanium alloy part ) 是由 闻强苗 陈晓红 吕振兴 王成 白晶莹 崔庆新 李思振 李国利 *** 于 2020-05-09 设计创作，主要内容包括：本发明涉及一种钛合金部件深腔螺纹局部离子渗氮的方法,属于化学热处理技术领域；步骤一、根据钛合金零件的尺寸形状制作渗氮工装；步骤二、对渗氮工装进行真空退火处理；步骤三、擦拭钛合金零件和渗氮工装,通过无油压缩空气或氮气吹干；步骤四、将渗氮工装包覆在钛合金零件的外壁；步骤五、重复步骤一至步骤四n次,制作n个包覆钛合金零件的渗氮工装；将n个渗氮工装呈环形均匀设置在电离圆盘上；n为正整数；步骤六、对钛合金零件进行渗氮处理；本发明通过工装设计保护零件外表面及深腔非渗部位无渗氮层,调节渗氮过程中温度、时间、气氛、电参数,使得整个深腔螺纹获得满足技术要求的渗氮层硬度、渗氮深度。(The invention relates to a method for local ion nitriding of a deep cavity thread of a titanium alloy part, belonging to the technical field of chemical heat treatment; manufacturing a nitriding tool according to the size and shape of the titanium alloy part; step two, carrying out vacuum annealing treatment on the nitriding tool; wiping the titanium alloy part and the nitriding tool, and drying by using oil-free compressed air or nitrogen; step four, coating the nitriding tool on the outer wall of the titanium alloy part; step five, repeating the step one to the step four n times, and manufacturing n nitriding tools for coating the titanium alloy parts; uniformly arranging n nitriding tools on an ionization disc in an annular shape; n is a positive integer; sixthly, nitriding the titanium alloy part; the invention protects the outer surface of the part and the non-nitriding part of the deep cavity from being provided with the nitriding layer through tool design, and adjusts the temperature, time, atmosphere and electrical parameters in the nitriding process, so that the whole deep cavity thread can obtain the hardness and the nitriding depth of the nitriding layer which meet the technical requirements.)

1. A method for local ion nitriding of deep cavity threads of a titanium alloy part is characterized by comprising the following steps: the method comprises the following steps:

step one, manufacturing a nitriding tool (2) according to the size and shape of the titanium alloy part (1);

step two, carrying out vacuum annealing treatment on the nitriding tool (2);

wiping the titanium alloy part (1) and the nitriding tool (2), and drying by using oil-free compressed air or nitrogen;

fourthly, coating the nitriding tool (2) on the outer wall of the titanium alloy part (1);

step five, repeating the step one to the step four n times to manufacture n nitriding tools (2) coated with the titanium alloy parts (1); uniformly arranging n nitriding tools (2) on an ionization disc (3) in an annular shape; n is a positive integer;

and sixthly, nitriding the titanium alloy part (1).

2. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 1, characterized in that: in the first step, the titanium alloy part (1) is of a columnar structure; a columnar through hole (11) is formed in the axis of the titanium alloy part (1) along the axis direction; the nitriding tool (2) is of a hollow shell structure; and the nitriding tool (2) is provided with exposed holes (21) with the same size corresponding to the positions of the columnar through holes (11).

3. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 2, characterized in that: in the second step, the specific method of the vacuum annealing treatment comprises the following steps:

s1, placing the nitriding tool (2) into a combustion furnace;

s2, carrying out vacuum pumping treatment on the combustion furnace;

s3, heating and insulating the combustion furnace;

and S4, cooling and discharging.

4. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 3, wherein: in the step two, in S2, the vacuum degree of the combustion furnace after vacuum pumping is better than 5 Pa; in the step S3, the heating rate is 8-15 ℃/min in the process of heating the combustion furnace; until the temperature is heated to 800-850 ℃; stopping heating, and keeping the temperature for 1-3 h; and S4, naturally cooling the combustion furnace, and discharging the nitriding tool (2) when the temperature of the combustion furnace is reduced to be less than 150 ℃.

5. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 4, wherein: in the third step, the titanium alloy part (1) and the nitriding tool (2) are wiped by adopting absolute ethyl alcohol; when in wiping, the outer wall of the titanium alloy part (1) and the inner wall of the columnar through hole (11) are wiped; and wiping the outer wall and the inner wall of the nitriding tool (2).

6. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 5, wherein: in the fourth step, when the nitriding tool (2) coats the titanium alloy part (1), the nitriding tool (2) is adjusted to completely cover the outer surface of the titanium alloy part (1), and meanwhile, two ends of the columnar through hole (11) of the titanium alloy part (1) are completely exposed through the exposure hole (21).

7. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 6, wherein: in the fifth step, n is an even number and is more than or equal to 4; the n nitriding tools (2) are all arranged along the radial direction of the ionization disc (3) in the axial direction.

8. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 7, characterized in that: in the sixth step, the specific method for nitriding the titanium alloy part (1) comprises the following steps:

s1, placing n nitriding tools (2) coated with titanium alloy parts (1) and an ionization disc (3) in a closed box;

s2, carrying out vacuum pumping treatment on the closed box body;

s3, heating and insulating the closed box;

s4, in the heat preservation process, filling mixed gas of nitrogen and argon into the closed box body;

s5, electrifying the ionization disc (3); generating an electric field in the closed box body, and ionizing nitrogen atoms and titanium atoms to generate titanium nitride;

and S6, cooling and taking out of the box to finish nitriding.

9. The method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to claim 8, characterized in that: in the step six, in S2, after the sealed box body is vacuumized, the vacuum degree is superior to 5 Pa; in S3, when the sealed box body is heated, the temperature rise rate of the sealed box body is 5-10 ℃/min; stopping heating until the temperature is 750-; in S4, the ratio of nitrogen to argon in the mixed gas is 3.0:0.1 to 3.0: 0.5; stopping inflating until the pressure in the closed box body is 400-800 Pa; in S5, the current is 30-60A, and the voltage is 400-600V; generating titanium nitride on the inner wall of the column-shaped through hole (11) exposed out of the titanium alloy part (1); s6, continuously filling a mixed gas of nitrogen and argon in the cooling process of the closed box body; until the temperature of the closed box body is reduced to be less than 50 ℃; and taking out the nitriding tool (2) for coating the titanium alloy part (1), and removing the nitriding tool (2) to finish nitriding the titanium alloy part (1).

10. Method for the local ion nitriding of deep-cavity threads of titanium alloy parts according to one of claims 1 to 9, characterized in that: the surface hardness HV of the nitrided titanium alloy part (1) is more than or equal to 650; depth D of deep nitrogen layer_ND is more than or equal to 0.015mm_N≤0.030mm。

Technical Field

The invention belongs to the technical field of chemical heat treatment, and relates to a method for local ion nitriding of deep cavity threads of a titanium alloy part.

Background

The titanium alloy has two remarkable advantages of high specific strength and good corrosion resistance, has excellent performances of high specific strength, high fatigue property, high corrosion resistance, low expansion coefficient, high stability and the like, and has good application prospect in the field of aerospace.

Because of the defects of low surface strength, low thermal conductivity, poor wear resistance and the like of the titanium alloy, the titanium alloy part is easy to adhere and bite in the assembling process, and further the part fails and even breaks. In order to improve the wear resistance of the titanium alloy, the surface strength is increased through ion nitriding surface modification treatment, so that the service life of parts is prolonged.

The ion nitriding is to utilize the rarefied nitrogen-containing gas to generate glow discharge to bombard and heat the surface of the metal material and form nitride for strengthening. The conventional nitriding treatment is mainly aimed at the outer surface of a part, the deep cavity thread nitriding is to carry out local nitriding on the inner thread of the part, meanwhile, the outer surface and the inner hole non-permeable part of the part need to be protected against seepage, and a protection device cannot hinder the normal nitriding of the deep cavity. When nitriding is carried out in the deep cavity, due to the characteristic of glow cathode voltage drop, a glow layer is difficult to penetrate into the deep cavity, so that the deep cavity cannot be nitrided or the depth distribution of the nitriding layer is uneven, and the use requirement of the wear resistance of the thread cannot be met.

Disclosure of Invention

The technical problem solved by the invention is as follows: the method overcomes the defects of the prior art, provides a method for local ion nitriding of the deep cavity thread of the titanium alloy part, protects the outer surface of the part and the non-nitriding part of the deep cavity without a nitriding layer through tool design, and adjusts the temperature, time, atmosphere and electrical parameters in the nitriding process so that the whole deep cavity thread obtains the hardness and the nitriding depth of the nitriding layer meeting the technical requirements.

The technical scheme of the invention is as follows:

a method for local ion nitriding of deep cavity threads of a titanium alloy part comprises the following steps:

manufacturing a nitriding tool according to the size and shape of the titanium alloy part;

step two, carrying out vacuum annealing treatment on the nitriding tool;

wiping the titanium alloy part and the nitriding tool, and drying by using oil-free compressed air or nitrogen;

step four, coating the nitriding tool on the outer wall of the titanium alloy part;

step five, repeating the step one to the step four n times, and manufacturing n nitriding tools for coating the titanium alloy parts; uniformly arranging n nitriding tools on an ionization disc in an annular shape; n is a positive integer;

and sixthly, nitriding the titanium alloy part.

In the above method for local ion nitriding of deep cavity threads of a titanium alloy part, in the first step, the titanium alloy part is in a columnar structure; a columnar through hole is formed in the axis of the titanium alloy part along the axis direction; the nitriding tool is of a hollow shell structure; and the position of the nitriding tool corresponding to the columnar through hole is provided with exposed holes with the same size.

In the above method for local ion nitriding of deep cavity threads of a titanium alloy part, in the second step, the specific method of vacuum annealing treatment is as follows:

s1, placing the nitriding tool into a combustion furnace;

s2, carrying out vacuum pumping treatment on the combustion furnace;

s3, heating and insulating the combustion furnace;

and S4, cooling and discharging.

In the above method for local ion nitriding of the deep cavity thread of the titanium alloy part, in step two, S2, the degree of vacuum after the furnace is vacuumized is better than 5 Pa; in the step S3, the heating rate is 8-15 ℃/min in the process of heating the combustion furnace; until the temperature is heated to 800-850 ℃; stopping heating, and keeping the temperature for 1-3 h; and S4, naturally cooling the combustion furnace, and discharging the nitriding tool when the temperature of the combustion furnace is reduced to less than 150 ℃.

In the method for local ion nitriding of the deep cavity threads of the titanium alloy part, in the third step, the titanium alloy part and a nitriding tool are wiped by absolute ethyl alcohol; when in wiping, the outer wall of the titanium alloy part and the inner wall of the columnar through hole are wiped; and wiping the outer wall and the inner wall of the nitriding tool.

In the fourth step, when the nitriding tool coats the titanium alloy part, the nitriding tool is adjusted to completely cover the outer surface of the titanium alloy part, and meanwhile, two ends of the columnar through hole of the titanium alloy part are completely exposed through the exposed hole.

In the above method for local ion nitriding of deep cavity threads of titanium alloy parts, in the fifth step, n is an even number and is greater than or equal to 4; the n nitriding tools are all arranged along the radial direction of the ionization disc in the axial direction.

In the sixth step, the specific method for performing nitriding treatment on the titanium alloy part comprises the following steps:

s1, placing n nitriding tools and ionizing discs coated with titanium alloy parts in a closed box;

s2, carrying out vacuum pumping treatment on the closed box body;

s3, heating and insulating the closed box;

s4, in the heat preservation process, filling mixed gas of nitrogen and argon into the closed box body;

s5, electrifying the ionization disc; generating an electric field in the closed box body, and ionizing nitrogen atoms and titanium atoms to generate titanium nitride;

and S6, cooling and taking out of the box to finish nitriding.

In the above method for local ion nitriding of the deep cavity thread of the titanium alloy part, in step six, in S2, after the closed box body is vacuumized, the vacuum degree is superior to 5 Pa; in S3, when the sealed box body is heated, the temperature rise rate of the sealed box body is 5-10 ℃/min; stopping heating until the temperature is 750-; in S4, the ratio of nitrogen to argon in the mixed gas is 3.0:0.1 to 3.0: 0.5; stopping inflating until the pressure in the closed box body is 400-800 Pa; in S5, the current is 30-60A, and the voltage is 400-600V; generating titanium nitride on the inner wall of the exposed columnar through hole of the titanium alloy part; s6, continuously filling a mixed gas of nitrogen and argon in the cooling process of the closed box body; until the temperature of the closed box body is reduced to be less than 50 ℃; and taking out the nitriding tool for coating the titanium alloy part, and removing the nitriding tool to finish nitriding the titanium alloy part.

According to the method for local ion nitriding of the deep cavity threads of the titanium alloy part, the surface hardness HV of a nitrided titanium alloy part is more than or equal to 650; depth D of deep nitrogen layer_ND is more than or equal to 0.015mm_N≤0.030mm。

Compared with the prior art, the invention has the beneficial effects that:

(1) aiming at the problem of nitriding the titanium alloy inner cavity threads, the nitriding tool is adopted, so that the outer surface of the titanium alloy can be ensured not to have a permeation layer, the inner cavity thread nitriding can be ensured not to be influenced, and the titanium alloy is supported by the tool, so that the glow nitriding process is better ensured;

(2) according to the invention, nitriding is carried out in a hydrogen-free atmosphere, the titanium alloy is easy to absorb hydrogen in a hydrogen atmosphere, and hydrogen embrittlement is easily generated when the hydrogen content in the titanium alloy reaches a certain degree, so that the titanium alloy is ineffective. The hydrogen-free nitriding can effectively avoid hydrogen embrittlement of the titanium alloy;

(3) the invention adopts ion nitriding, which adopts a mode of bombarding the surface of the titanium alloy by plasma, can effectively shorten nitriding time and greatly improve the working efficiency compared with gas nitriding;

(4) the invention can adjust the electrical parameter in the nitriding process, and can meet the requirement of uniform distribution of the nitriding layer along the threads of the inner cavity;

(5) the nitriding layer can be prepared on the threaded surface of the inner cavity of the titanium alloy part, through surface Vickers hardness detection, metallographic observation and scanning electron microscope observation, the hardness and nitriding of the nitriding layer meet the requirements, and the nitriding layer is uniform and free of defects. The non-nitrided matrix developed a slight corrosion under 7 hours of salt spray corrosion, while no significant corrosion was seen in the nitrided parts. The nitriding layer can realize accurate control, and the following technical index requirements are met: the surface hardness HV of the nitriding part is more than or equal to 650; DN is more than or equal to 0.015mm and less than or equal to 0.030 mm.

Drawings

FIG. 1 is a schematic view of a titanium alloy part of the present invention;

FIG. 2 is a schematic view of a nitriding tool according to the present invention;

FIG. 3 is a schematic view showing the distribution of the nitriding tool on an ionization disc according to the present invention;

FIG. 4 is a diagram of the metallographic detection effect of the present invention.

Detailed Description

The invention is further illustrated by the following examples.

The invention provides a method suitable for local ion nitriding of deep cavity threads of a titanium alloy part. The outer surface of the part and the non-nitriding part of the deep cavity are protected from a nitriding layer through tool design, and the temperature, time, atmosphere and electrical parameters in the nitriding process are adjusted, so that the whole deep cavity thread can obtain the hardness and the nitriding depth of the nitriding layer meeting the technical requirements.

The specific process comprises the following steps:

firstly, manufacturing a nitriding tool 2 according to the size and shape of a titanium alloy part 1; as shown in fig. 1, the titanium alloy part 1 has a columnar structure; a columnar through hole 11 is formed in the axis of the titanium alloy part 1 along the axis direction; the nitriding tool 2 is of a hollow shell structure; as shown in fig. 2, the nitriding tool 2 is provided with exposure holes 21 having the same size at positions corresponding to the columnar through holes 11.

Step two, carrying out vacuum annealing treatment on the nitriding tool 2; the specific method of the vacuum annealing treatment comprises the following steps:

s1, placing the nitriding tool 2 into a combustion furnace.

S2, carrying out vacuum pumping treatment on the combustion furnace; the vacuum degree of the furnace after vacuum pumping is better than 5 Pa.

S3, heating and insulating the combustion furnace; in the heating process of the combustion furnace, the heating rate is 8-15 ℃/min; until the temperature is heated to 800-850 ℃; stopping heating, and keeping the temperature for 1-3 h.

And S4, cooling and discharging, naturally cooling the combustion furnace, and discharging the nitriding tool 2 when the temperature of the combustion furnace is reduced to be less than 150 ℃. .

Wiping the titanium alloy part 1 and the nitriding tool 2, and wiping the titanium alloy part 1 and the nitriding tool 2 by adopting absolute ethyl alcohol; when wiping, wiping the outer wall of the titanium alloy part 1 and the inner wall of the columnar through hole 11; and wiping the outer wall and the inner wall of the nitriding tool 2. Blow-drying by oil-free compressed air or nitrogen.

Fourthly, coating the outer wall of the titanium alloy part 1 with a nitriding tool 2; when the nitriding tool 2 coats the titanium alloy part 1, the nitriding tool 2 is adjusted to completely cover the outer surface of the titanium alloy part 1, and meanwhile, two ends of the columnar through hole 11 of the titanium alloy part 1 are completely exposed through the exposed hole 21.

Step five, repeating the step one to the step four n times, and manufacturing n nitriding tools 2 for coating the titanium alloy parts 1; uniformly arranging n nitriding tools 2 on an ionization disc 3 in an annular shape; n is a positive integer; n is an even number and is greater than or equal to 4; the n nitriding tools 2 are all arranged along the radial direction of the ionization disc 3 in the axial direction, as shown in figure 3.

And sixthly, nitriding the titanium alloy part 1. The specific method for nitriding the titanium alloy part 1 comprises the following steps:

s1, placing n nitriding tools 2 coated with titanium alloy parts 1 and an ionization disc 3 in a closed box;

s2, carrying out vacuum pumping treatment on the closed box body; after the sealed box body is vacuumized, the vacuum degree is superior to 5 Pa.

S3, heating and insulating the closed box; when the closed box body is heated, the temperature rise rate of the closed box body is 5-10 ℃/min; stopping heating until the temperature is 750-850 ℃, and preserving the heat for 10-20 h.

S4, in the heat preservation process, filling mixed gas of nitrogen and argon into the closed box body; the ratio of nitrogen to argon in the mixed gas was 3.0:0.1 to 3.0: 0.5; and stopping inflating until the pressure in the closed box body is 400-800 Pa.

S5, electrifying the ionization disc 3; generating an electric field in the closed box body, and ionizing nitrogen atoms and titanium atoms to generate titanium nitride; the electrified current is 30-60A, and the voltage is 400-600V; titanium nitride is formed on the inner wall of the columnar through hole 11 exposed from the titanium alloy part 1.

And S6, cooling and taking out of the box to finish nitriding. The specific process is that in the cooling process of the closed box body, the mixed gas of nitrogen and argon is continuously filled; until the temperature of the closed box body is reduced to be less than 50 ℃; and taking out the nitriding tool 2 for coating the titanium alloy part 1, and removing the nitriding tool 2 to finish nitriding the titanium alloy part 1.

The surface hardness HV of the nitrided titanium alloy part 1 is more than or equal to 650; depth D of deep nitrogen layer_ND is more than or equal to 0.015mm_NIs less than or equal to 0.030mm, and the metallographic detection effect graph is shown in figure 4.