CN112410722B - Alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment and nitride layer forming method thereof - Google Patents
Alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment and nitride layer forming method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of titanium alloy nitriding, in particular to an alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment and a nitride layer forming method thereof. The nitride layer forming method of the present invention includes the steps of: sequentially quenching, cold forming and low-temperature nitriding the alpha + beta type titanium alloy to form a nitride layer on the surface of the alpha + beta type titanium alloy; the accumulated deformation of the cold forming is 10-65%; the temperature of the low-temperature nitridation is 400-600 ℃. The method can form a millimeter-scale ultra-thick nitrided layer on the surface of the alpha + beta type titanium alloy, has adjustable hardness gradient, can obviously improve the ductility and toughness of an alloy matrix structure and the wear resistance of the titanium alloy, improves the fatigue damage resistance of a carburized layer, and prolongs the service life of a product.
Description
Technical Field
The invention relates to the technical field of titanium alloy nitriding, in particular to an alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment and a nitride layer forming method thereof.
Background
Titanium metal, one of the most abundant metals in crust resources, has been developed for over two hundred years, and is increasingly applied to the fields of national defense industry, chemical industry, energy and the like today. Several hundred titanium alloys have been developed with different compositions and properties.
One class of titanium alloys has dual phase (α + β) characteristics, such as TC4, TC11, TC17, and TC21. The biggest restricting factors of the titanium alloy in application are relatively low strength and poor surface wear resistance, but the currently researched improvement means mostly adopt a surface treatment technology to improve the hardness and wear resistance of the titanium alloy, wherein the nitriding process is widely applied by the advantages of simple process, firm bonding of a diffusion layer and a substrate, high relative hardness of titanium nitride and the like.
At present, the nitriding treatment temperature of the alpha + beta type titanium alloy is concentrated at about 900 ℃, and the nitriding treatment under the high-temperature condition can cause the grain size in the titanium alloy matrix to be increased and reduce the toughness of the matrix. And the thickness of the conventional high-temperature (900 ℃) nitriding penetration layer can only reach the nanometer or micron level, so that the wear resistance of the titanium alloy is poor.
Disclosure of Invention
The invention aims to provide a method for forming an alpha + beta type titanium alloy nitride layer based on cold forming composite low-temperature nitriding treatment.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for forming an alpha + beta type titanium alloy nitride layer based on cold forming composite low-temperature nitriding treatment, which comprises the following steps of: sequentially quenching, cold forming and low-temperature nitriding the alpha + beta type titanium alloy to form a nitride layer on the surface of the alpha + beta type titanium alloy; the accumulated deformation of the cold forming is 10-65%; the low-temperature nitriding temperature is 400-600 ℃, and the low-temperature nitriding time is not less than 2h;
preferably, after the low-temperature nitridation, the titanium alloy after the low-temperature nitridation is subjected to thermal diffusion treatment; the temperature of the thermal diffusion treatment is 200-400 ℃.
Preferably, the thickness of the nitride layer is greater than 1mm.
Preferably, the quenching cooling mode is to use circulating water at 15 ℃ for cooling.
Preferably, the low-temperature nitridation is performed in a mixed atmosphere of nitrogen and hydrogen.
Preferably, the flow ratio of the nitrogen gas to the hydrogen gas is 1.
Preferably, the low-temperature nitridation is carried out in a pulse plasma furnace, the voltage is 650V, the pressure rise rate is 0.13P/min, and the duty ratio is 15-75%.
Preferably, the thermal diffusion treatment is performed under vacuum conditions.
The invention provides an alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment, wherein the surface of the alpha + beta type titanium alloy is provided with a nitriding layer, and the nitriding layer is prepared by the alpha + beta type titanium alloy nitriding layer forming method in the scheme; the thickness of the nitride layer is more than 1mm.
Preferably, the nitride layer has a concentration gradient of N atoms from the surface to the inside.
The invention provides a method for forming an alpha + beta type titanium alloy nitride layer based on cold forming composite low-temperature nitriding treatment, which comprises the following steps of: sequentially quenching, cold forming and low-temperature nitriding the alpha + beta type titanium alloy to form a nitride layer on the surface of the alpha + beta type titanium alloy; the accumulated deformation of the cold forming is 10-65%; the low-temperature nitridation temperature is 400-600 ℃, and the low-temperature nitridation time is not less than 2h. The invention quenches the alpha + beta type titanium alloy, can obtain martensite to the greatest extent after quenching, the martensite is softer, and is more beneficial to subsequent integral cold forming, and simultaneously, the appearance of a large amount of martensite enables that more defects such as dislocation, crystal boundary and the like are generated in the whole workpiece than the process of solid solution treatment and integral cold forming after integral cold forming, a large amount of channels are provided for the diffusion of N atoms in the nitriding process, and the recrystallization is promoted to the greatest extent, so that the low-temperature nitriding and the formation of a millimeter-scale ultra-thick nitride layer become possible; and then, low-temperature nitridation is carried out, the influence of early-stage cold forming is received, partial recrystallization phenomenon appears in the matrix structure at the nitridation temperature, recrystallization means grain refinement, the grain refinement can increase the comprehensive performance of the matrix, and simultaneously, the grain boundary is increased, which means that the channel for N atom diffusion is increased, and N atoms can enter the matrix more easily, so that the recrystallization also has a permeation promoting effect, and the millimeter-grade ultra-thick nitride layer can be obtained. Meanwhile, because the nitriding temperature is set within the aging temperature, intermetallic compounds are precipitated through aging in the low-temperature nitriding process, so that a superimposed strengthening effect is generated, the surface performance is improved, and the core plastic toughness is improved.
Furthermore, the invention carries out thermal diffusion treatment after low-temperature nitriding, and because a large number of diffusion channels are formed in the metal matrix in the cold deformation and recrystallization processes, N atoms can be diffused into the matrix far away and greatly exceed the distance which can be reached by the existing nitriding process, under the condition of low-temperature thermal diffusion, atoms in a diffusion layer can be continuously diffused inwards, the thickness of a nitriding layer is further increased, and the distribution gradient of N in the nitriding layer can be adjusted, so that the tissue distribution is influenced, the hardness gradient from the outside to the inside is adjusted, the fatigue damage resistance of the diffusion layer is improved, and the service life of a product is prolonged.
Drawings
FIG. 1 is a crystal grain orientation diagram (a) of the TC4 alloy of example 1 after quenching and cold forming and a crystal grain orientation diagram (b) after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment;
FIG. 2 is a metallographic photograph (a) of a base of the TC4 alloy of example 1 after quenching and cold forming and a metallographic photograph (b) of a base of the alloy after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment;
FIG. 3 is a hardness gradient profile of the TC4 alloy of example 1 after quenching, cold forming, low temperature nitriding, and thermal diffusion treatment;
FIG. 4 is a hardness gradient profile of the TC4 alloy of example 2 after quenching, cold forming, low temperature nitriding, and thermal diffusion treatment;
FIG. 5 is a hardness gradient profile of the TC4 alloy of example 3 after quenching, cold forming, low temperature nitriding, and thermal diffusion treatment;
fig. 6 is an XRD phase analysis pattern of the TC4 alloy after being treated under the process of example 1 while varying the cold-formed deformation amount.
Detailed Description
The invention provides a method for forming an alpha + beta type titanium alloy nitride layer based on cold forming composite low-temperature nitriding treatment, which comprises the following steps of: sequentially quenching, cold forming and low-temperature nitriding the alpha + beta type titanium alloy to form a nitride layer on the surface of the alpha + beta type titanium alloy; the accumulated deformation of the cold forming is 10-65%; the temperature of the low-temperature nitridation is 400-600 ℃.
The specific type of the α + β titanium alloy is not particularly required in the present invention, and any α + β titanium alloy known in the art may be used. In the present invention, the α + β type titanium alloy preferably includes TC4, TC8, TC11, TC17 or TC21.
The invention quenches the alpha + beta type titanium alloy. The invention has no special requirements on the quenching temperature and the quenching heat preservation time, and the corresponding quenching process well known in the field is selected according to the type of the alpha + beta type titanium alloy. In the present invention, the quenching is preferably performed by cooling with circulating water at 15 ℃. In the invention, when the alpha + beta type titanium alloy is TC4, the quenching temperature is preferably 850 ℃, the holding time is preferably 50min, and the cooling mode is preferably cooling by adopting circulating water at 15 ℃. In the present invention, the quenching is preferably performed in a vacuum furnace. The invention quenches the alpha + beta type titanium alloy, can obtain martensite to the greatest extent after quenching, the martensite is softer, and is more beneficial to subsequent integral cold forming, and simultaneously, the appearance of a large amount of martensite leads the interior of the whole workpiece to generate more defects such as dislocation, crystal boundary and the like compared with the process of solid solution treatment and integral cold forming after integral cold forming.
After the quenching is finished, the obtained quenched titanium alloy is subjected to cold forming (namely cold forming), so that a titanium alloy workpiece is obtained. In the present invention, the cumulative deformation amount of the cold forming is 10 to 65%, preferably 20 to 50%, more preferably 30 to 40%. When the deformation of the titanium alloy is less than 10%, the invention preferably performs pre-deformation before cold forming to ensure that the accumulated deformation of the workpiece to be treated before low-temperature nitridation is within the range. The present invention preferably performs cold forming at room temperature. The cold forming process is not particularly required by the present invention, and the cold forming process known in the art can be adopted, and particularly, but not limited to, spin forming. The invention controls the accumulated deformation of cold forming in the range, so that a great deal of defects are generated in the workpiece, and a channel is provided for N atoms to permeate, thereby increasing the thickness of the nitride layer. The present invention may be further optimized within the above-described deformation amount according to the requirements for the overall hardness and hardness gradient of the nitride layer, which will be described in detail later.
After the cold forming is finished, the obtained titanium alloy workpiece is subjected to low-temperature nitridation.
Before the low-temperature nitridation, the method preferably further comprises the steps of polishing the surface of the titanium alloy workpiece by using sand paper, and carrying out ultrasonic cleaning on the polished titanium alloy workpiece in an acetone solution. The invention has no special requirements on the polishing and ultrasonic cleaning processes, and can remove impurities on the surface of the titanium alloy workpiece. The invention is beneficial to the low-temperature nitridation through grinding and ultrasonic cleaning.
In the present invention, the low-temperature nitriding temperature is 400 to 600 ℃, preferably 450 to 550 ℃, and more preferably 480 to 500 ℃. In the invention, the time of low-temperature nitridation is not less than 2h. In the invention, the longer the heat preservation time of low-temperature nitridation is, the thicker the infiltrated layer is, and the hardness gradient becomes slow, and the skilled person can regulate and control the heat preservation time according to the rule.
In the invention, when the deformation of cold forming is 20-40%, and the temperature of low-temperature nitriding is 480 ℃, and the holding time of low-temperature nitriding is more than 2h, the thickness of the infiltrated layer can reach more than 1mm. Specifically, when the heat preservation time is 14 hours, the thickness of the infiltration layer can reach 3.6mm, and when the heat preservation time is prolonged to 16 hours, the thickness of the infiltration layer can reach 4mm; when the heat preservation time is continuously prolonged to 18 hours, the thickness of the infiltration layer can reach 4.4mm.
In the present invention, the low-temperature nitriding is preferably performed in a mixed atmosphere of nitrogen and hydrogen, and the flow ratio of nitrogen to hydrogen is preferably 1. In the present invention, the low-temperature nitridation is preferably performed in a pulsed plasma furnace, the voltage is preferably 650V, the pressure rise rate is preferably 0.13P/min, and the duty ratio is preferably 15 to 75%, more preferably 20 to 70%, and still more preferably 30 to 60%.
In the low-temperature nitriding process, under the influence of early-stage cold forming, a matrix structure has a partial recrystallization phenomenon at the nitriding temperature, the recrystallization means grain refinement, which can increase the comprehensive performance of the matrix, and simultaneously, the grain boundary is increased, which means that N atom diffusion channels are increased, and N atoms can enter the matrix more easily, so that the recrystallization also has a permeation promoting effect, and the millimeter-grade (namely more than 1 mm) ultra-thick nitride layer can be obtained. Meanwhile, because the nitriding temperature is set within the aging temperature, intermetallic compounds are precipitated through aging in the low-temperature nitriding process, so that a superimposed strengthening effect is generated, the surface performance is improved, and the core plastic toughness is improved. After the titanium alloy is subjected to low-temperature nitridation, the number of nitrides is gradually reduced from the surface layer to the core part, and the number of intermetallic compounds is gradually increased and is in continuous gradient distribution. In addition, because the nitriding temperature is low, nitriding can be carried out for a long time without worrying about weakening of internal tissues, and meanwhile, cold forming generates a large number of nitrogen atom diffusion channels, so that a white and bright layer (nitride) on the surface disappears, and the diffusion layer is greatly expanded, thereby being much thicker than a penetration layer obtained by high-temperature nitriding.
Those skilled in the art can select the quenching temperature, the accumulated deformation of cold forming and the low-temperature nitriding temperature according to the actual requirement according to the relationship between the quenching temperature, the accumulated deformation of cold forming and the hardness of the nitrided layer. Specifically, the method comprises the following steps:
when the quenching temperature is high (> 800 ℃), the accumulated deformation is large (35-65%) and the low-temperature nitriding temperature is 400-480 ℃, the hardness gradient of the formed nitride layer is greatly changed, and the overall hardness is relatively high (above 800 HV);
when the quenching temperature is high (> 800 ℃), the accumulated deformation is large (35-65%) and the low-temperature nitriding temperature is 500-600 ℃, the hardness gradient of the nitrided layer is small and the overall hardness is relatively high (above 800 HV);
when the quenching temperature is low (less than or equal to 750 ℃), the accumulated deformation is small (10-25%), and the low-temperature nitriding temperature is 400-480 ℃, the hardness gradient of the nitrided layer is greatly changed, and the overall hardness is relatively low (below 700 HV);
when the quenching temperature is low (less than or equal to 750 ℃), the accumulated deformation is small (10-25%), and the low-temperature nitriding temperature is 500-600 ℃, the hardness gradient change of the nitride layer is small, and the overall hardness is relatively low (below 700 HV);
when the quenching temperature is moderate (> 750 ℃ and less than or equal to 800 ℃), the deformation is moderate (25-35%) and the low-temperature nitriding temperature is 480-500 ℃, the hardness gradient change of the nitride layer is moderate, and the overall hardness is moderate (700-800 HV).
The hardness gradient of the nitride layer is changed greatly, slightly or moderately, which is described purely regularly relative to the processing conditions of the invention and has no specific range.
In the invention, after low-temperature nitridation, the thickness of the formed nitride layer can reach more than 1mm.
After the low-temperature nitridation is completed, the invention preferably further comprises the step of carrying out thermal diffusion treatment on the titanium alloy subjected to the low-temperature nitridation to form an ultra-thick nitrided layer on the surface of the alpha + beta type titanium alloy. In the present invention, the temperature of the thermal diffusion treatment is 200 to 400 ℃, preferably 220 to 300 ℃. The invention has no special requirement on the time of the thermal diffusion treatment, and particularly, the hardness gradient of the nitride layer becomes more gradual as the thermal diffusion treatment time is longer under the same thermal diffusion treatment temperature; the shorter the time of the thermal diffusion treatment, the smaller the gradual range of the hardness gradient of the nitrided layer. The selection of the thermal diffusion treatment time can be made by those skilled in the art according to this law.
In the present invention, the time when the heat diffusion treatment is carried out is preferably not less than 2 hours. In the present invention, when the temperature of the thermal diffusion treatment is 200 ℃ and the time of the thermal diffusion treatment is 3 hours, the nitrogen atom concentration on the surface of the nitride layer is preferably 15 to 30%, more preferably 19 to 25%.
In the present invention, the thermal diffusion treatment is preferably performed under vacuum conditions. The degree of vacuum is preferably 30Pa or less.
Because a large number of diffusion channels are formed in the metal matrix in the cold deformation and low-temperature nitridation recrystallization processes, N atoms can be diffused into the matrix far away and greatly exceed the distance which can be achieved by the conventional nitridation process, under the condition of low-temperature thermal diffusion, atoms in a diffusion layer can be continuously diffused inwards, the thickness of a nitrided layer is further increased, and the distribution gradient of N can be adjusted, so that the tissue distribution is influenced, and the hardness gradient from the outside to the inside is adjusted.
In the present invention, the concentration of nitrogen atoms in the nitrided layer gradually decreases from the outside to the inside after the thermal diffusion treatment.
In the invention, the thickness of the nitride layer formed after the thermal diffusion treatment is further increased compared with the thickness of the nitride layer formed after the low-temperature nitridation, and in the embodiment of the invention, the thickness can reach 3.6-4.4 mm.
The invention provides an alpha + beta type titanium alloy based on cold forming composite low-temperature nitriding treatment, wherein the surface of the alpha + beta type titanium alloy is provided with a nitriding layer, and the nitriding layer is obtained by the alpha + beta type titanium alloy nitriding layer forming method in the scheme; the thickness of the nitride layer is more than 1mm.
In the present invention, when the α + β type titanium alloy after low-temperature nitriding is further subjected to thermal diffusion treatment, the nitrided layer also has a nitrogen atom concentration gradient from the surface to the inside.
The surface of the alpha + beta type titanium alloy has a millimeter-grade ultra-thick nitrided layer and a certain hardness gradient, so that the plasticity and toughness of an alloy matrix structure and the wear resistance of the titanium alloy can be obviously improved, the fatigue damage resistance of a carburized layer is improved, and the service life of a product is prolonged.
The following will describe in detail the method for forming an ultra-thick nitrided layer of α + β titanium alloy based on cold forming combined low-temperature nitriding treatment according to the present invention with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Example 1
In this embodiment, a TC4 titanium alloy sheet is taken as a processing object, and the specific steps are as follows:
quenching treatment: putting the TC4 titanium alloy into a vacuum furnace, preserving heat at 850 ℃ for 50min, and cooling with circulating water at 15 ℃;
cold forming: after quenching, cold working forming is carried out at room temperature, the deformation is 30%, and a TC4 titanium alloy sheet piece is obtained;
cleaning a workpiece: polishing the surface of a workpiece by using sand paper, and performing ultrasonic cleaning in an acetone solution;
low-temperature nitridation: putting the cleaned workpiece in a pulse plasma furnace, wherein the selected atmosphere in the nitriding process is N 2 And H 2 Two gas permeation agents with the flow ratio of 1,N 2 、H 2 Flow rate is uniformIs 0.21m 3 The voltage is 650V, the pressure rise rate is 0.13P/min, the duty ratio is 45%, the nitriding temperature is 480 ℃, and the heat preservation time is 16h;
thermal diffusion treatment: and (3) preserving the temperature of the obtained nitriding workpiece at 200 ℃ for 3h to form a nitriding layer on the surface of the workpiece.
FIG. 1 is a crystal grain orientation diagram (a) of the TC4 alloy of example 1 after quenching and cold forming and a crystal grain orientation diagram (b) after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment. As can be seen from fig. 1, the grain size is reduced after the low-temperature nitriding and the thermal diffusion treatment, and the preferred orientation of the grains is changed, which indicates that the toughness of the TC4 alloy is improved after the quenching, the cold forming, the low-temperature nitriding and the thermal diffusion treatment.
FIG. 2 shows metallographic images of the matrix (a) of the TC4 alloy of example 1 after quenching and cold forming and metallographic images of the matrix (b) of the TC4 alloy after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment, and it can be seen from FIG. 2 that the original deformed morphology is maintained after low-temperature nitriding, but the structure is further refined, and the black aging precipitate phase is increased, indicating that sufficient aging occurs during the low-temperature nitriding process.
The TC4 titanium alloy thin plate member after quenching and cold forming, the nitrided workpiece obtained by quenching, cold forming and low-temperature nitriding and the nitrided workpiece obtained by quenching, cold forming, low-temperature nitriding and thermal diffusion treatment in example 1 were examined, and the results showed that the TC4 alloy friction coefficient after only quenching and cold forming was 0.60 and the surface hardness reached 355HV; after low-temperature nitridation, the thickness of a nitrided workpiece infiltrated layer is 2.8mm, and the surface N concentration is 24.5% (referring to the number percentage of N atoms); after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment, the surface N concentration of the TC4 alloy is 23%, the core N concentration is 19.8%, the thickness of a diffusion layer is 4mm, the friction coefficient is 0.26, the surface hardness reaches 650HV, and the hardness of a matrix after thermal diffusion treatment is in a step change, as shown in FIG. 3.
It is shown that only quenching and cold forming are performed, and the hardness and wear resistance of the TC4 alloy are improved to a certain extent compared with those of the as-fed TC4 alloy, but are still poorer than those of the TC4 alloy after quenching, cold forming, low-temperature nitriding and thermal diffusion treatment. In addition, it can be said that the thermal diffusion treatment can further increase the thickness of the permeated layer.
Example 2
Example 2 is different from example 1 in that the cold forming deformation amount is 20% and the nitriding time is 14 hours.
The nitrided work piece obtained after the low-temperature nitridation of example 2 and the nitrided work piece obtained after the thermal diffusion treatment were examined, and the results show that the thickness of the carburized layer of the nitrided work piece after the low-temperature nitridation of example 2 was 2.3mm, and the surface N concentration was 21.6%; the surface N concentration of the TC4 alloy after the thermal diffusion treatment is 19%, the core concentration is 15.6%, the diffusion layer thickness is 3.6mm, the friction coefficient is 0.39, the surface hardness reaches 632HV, and the hardness of the matrix after the thermal diffusion treatment is in a step change, as shown in figure 4.
Example 3
Example 3 is different from example 1 in that the cold forming deformation amount is 40% and the nitriding time is 18 hours.
The nitrided work piece obtained after the low-temperature nitriding in example 3 and the nitrided work piece obtained after the thermal diffusion treatment were examined, and the results show that the thickness of the carburized layer of the nitrided work piece after the low-temperature nitriding in example 3 was 3mm and the surface N concentration was 26.9%; the surface N concentration of the TC4 alloy after the thermal diffusion treatment is 25%, the core concentration is 22.3%, the diffusion layer thickness is 4.4mm, the friction coefficient is 0.24, the surface hardness reaches 661HV, and the hardness of the matrix after the thermal diffusion treatment is in a step change, as shown in FIG. 5.
The comprehensive performance of the products of the examples 1 to 3 is far better than that of the TC4 titanium alloy in the incoming material state (the hardness is 310HV, and the friction coefficient is 0.69), and therefore, the hardness and the wear resistance of the titanium alloy treated by the method are greatly improved, and a certain N concentration gradient is generated.
Examples 4 to 7
The difference from example 1 is that the cold-forming deformation amounts were 10%, 20%, 40% and 50%, respectively.
Comparative example 1
The difference from example 1 is that cold forming was not performed, that is, the deformation amount of cold forming was 0%.
Comparative example 1 the surface N concentration of the TC4 alloy after treatment was 9%, no N element was detected in the core, the infiltrated layer thickness was 60 μm, the friction coefficient was 0.52, and the surface hardness reached 410HV.
From the results of example 1 and comparative example 1, it is understood that the resulting infiltrated layer is thin without cold forming, and the surface hardness and wear resistance are poor.
Fig. 6 is an XRD phase analysis pattern after treating the TC4 alloy under the process of example 1 by changing the deformation amount of cold forming (corresponding products are specifically the products of example 1, examples 4 to 7, and comparative example 1). As can be seen from FIG. 6, tiN phases were present in the case of different deformation amounts, indicating that nitrides were formed in the case of different deformation amounts.
Comparative example 2
The difference from the example 1 is that the quenching treatment is changed into the solution treatment, the temperature of the solution treatment is 820 ℃, the holding time is 1h, and the heat diffusion treatment process is not needed, and the rest is the same as the example 1.
The penetrated layer obtained in comparative example 2 had a thickness of 60 μm, a surface hardness of 661HV, and a friction coefficient of 0.3.
The reason why the diffusion layer of the embodiment 1 is thicker than that of the comparative example 2 is that the solid solution treatment is changed into the quenching treatment, so that more defects such as dislocation, grain boundaries and the like are generated in the whole workpiece than the process of 'solid solution treatment + integral cold forming', a large number of channels are provided for the diffusion of N atoms in the nitriding process, the recrystallization is promoted to the greatest extent, and the diffusion of the nitrogen atoms is facilitated; meanwhile, the thermal diffusion can enable the diffusion of the atoms in the diffusion layer to continue inward, the thickness of the nitride layer is further increased, and the obtained diffusion layer is thicker.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (9)
1. A method for forming an alpha + beta type titanium alloy nitride layer based on cold forming composite low-temperature nitriding treatment comprises the following steps: sequentially carrying out quenching, cold forming, low-temperature nitriding and thermal diffusion treatment on the alpha + beta type titanium alloy to form a nitride layer on the surface of the alpha + beta type titanium alloy; the accumulated deformation of the cold forming is 10-65%; the temperature of the low-temperature nitridation is 400-600 ℃, and the time of the low-temperature nitridation is 2-18 h; the temperature of the thermal diffusion treatment is 200-300 ℃.
2. The method for forming an α + β type titanium alloy nitride layer according to claim 1, wherein the thickness of the nitride layer is larger than 1mm.
3. The method for forming an α + β titanium alloy nitride layer according to claim 1, wherein the quenching is performed by cooling with circulating water at 15 ℃.
4. The method for forming an α + β type titanium alloy nitride layer according to claim 1, wherein the low temperature nitridation is performed in a mixed atmosphere of nitrogen and hydrogen.
5. The α + β type titanium alloy nitride layer forming method according to claim 4, wherein a flow ratio of the nitrogen gas and the hydrogen gas is 1.
6. The method for forming an α + β type titanium alloy nitrided layer according to claim 1, 4 or 5, wherein the low temperature nitriding is carried out in a pulsed plasma furnace at a voltage of 650V, a pressure rise rate of 0.13P/min and a duty ratio of 15 to 75%.
7. The method for forming an α + β type titanium alloy nitride layer according to claim 1, wherein the thermal diffusion treatment is performed under vacuum conditions.
8. An α + β type titanium alloy based on cold forming combined low-temperature nitriding treatment, the α + β type titanium alloy having a nitrided layer on a surface thereof, the nitrided layer being produced by the α + β type titanium alloy nitrided layer forming method according to any one of claims 1 to 7; the thickness of the nitride layer is more than 1mm.
9. The α + β titanium alloy according to claim 8, wherein said nitride layer has a concentration gradient of N atoms from the surface to the inside.
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