A method for laser nitriding-hipping treatment of titanium alloy surface

Abstract

The application relates to the alloy technical field and provides a laser nitriding-thermal isostatic pressing treatment method for a titanium alloy surface, which sequentially performs laser nitriding treatment and thermal isostatic pressing on the titanium alloy surface to complete the treatment of the titanium alloy. First, a cermet nitriding layer is prepared on the titanium alloy surface through laser nitriding treatment, so that the strength of the titanium alloy is improved; then, the internal defects are eliminated and the organizational uniformity is improved through thermal isostatic pressing; the strength and toughness of the titanium alloy modification layer material and the tribological performance are simultaneously improved through the two steps of laser nitriding and thermal isostatic pressing. The treatment method can improve the strength of the titanium alloy through the precipitated TiN ceramic phase, the hardness of the titanium alloy is improved by 60Hv after the treatment, and the plasticity, toughness and friction performance are also improved; the friction coefficient is reduced from 1.3 to 1.07 at room temperature, the wear rate is reduced from 6.9*10 ‑5 mm 3 / (N·m) to 1.9*10 ‑5 mm 3 / (N·m) at 500 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy, in particular to a laser nitriding- hot isostatic pressing treatment method for titanium alloy surface. BACKGROUND

[0002] Titanium alloy has irreplaceable application in aerospace, medical and other fields due to its superior physical and chemical properties, and the wear resistance of titanium alloy surface limits its further application and service life. It is an important engineering research problem to select a reasonable surface treatment method to improve the hardness and wear resistance of the titanium alloy surface. Among them, laser selective melting (SLM) assisted nitrogen in-situ preparation of cermet nitriding layer (TiN-Ti) on the surface of titanium alloy is the most effective surface strengthening process currently applicable to such large titanium alloy complex shaped parts, which can be implemented in conventional environment and is easy to combine with robots and other equipment, has high production efficiency, good flexibility and adaptability to complex shaped workpieces, and has wide industrial application. However, the high local heat input triggered by laser processing process causes high-speed cooling (105-107K / s) and high temperature gradient (103-104K / mm), which causes incomplete homogeneous diffusion, forms a supersaturated solid solution, and the non-equilibrium small volume molten pool is constrained by the solidified material in this area, thereby producing residual tensile stress. At the same time, there are great differences in melting point, thermal expansion coefficient and Young's modulus between the ceramic phase and the metal phase, and the interaction time is short, which further accumulates thermal stress, and high thermal stress causes deformation in the material, generates a large number of dislocations, and the blocking effect of solid solution elements on dislocation propagation, so the dislocations tend to accumulate in the interdendritic region to form dislocation cells. The non-uniformly distributed high residual stress and metastable structure will amplify the crack sensitivity of the modified layer, increase the hardness and brittleness of the modified layer, and reduce the ductility. In addition, rapid cooling also causes some special phase changes, such as complete phase change of Ti-based material β--α+α' phase; lives phase is formed in Ni-based material. In summary, how to enhance the toughness and plasticity of cermet material without sacrificing too much strength has become a problem to be solved. SUMMARY

[0003] The purpose of the present application is to overcome the problems in the prior art and provide a laser nitriding- hot isostatic pressing treatment method for titanium alloy surface.

[0004] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical scheme:

[0005] The present application provides a laser nitriding- hot isostatic pressing treatment method for titanium alloy surface, comprising the following steps:

[0006] The laser nitriding treatment and hot isostatic pressing are sequentially performed on the titanium alloy surface to complete the treatment of the titanium alloy.

[0007] Preferably, the laser nitriding treatment is performed in a nitrogen atmosphere; the input flow rate of the nitrogen is 5-10 L / min.

[0008] Preferably, the laser output power of the laser nitriding treatment is 1500-2500 W.

[0009] Preferably, the spot diameter of the laser nitriding treatment is 2-6 mm.

[0010] Preferably, the distance between the nozzle and the substrate of the laser nitriding treatment is 2-10 mm.

[0011] Preferably, the scanning speed of the laser nitriding treatment is 0.01-0.1 m / min.

[0012] Preferably, the heating rate of the hot isostatic pressing is 5-10 ℃ / min.

[0013] Preferably, the target temperature of the hot isostatic pressing is 900-1100 ℃.

[0014] Preferably, the holding time of the hot isostatic pressing is 2-4 h.

[0015] Preferably, the holding pressure of the hot isostatic pressing is 120-150 MPa.

[0016] The present application has the following advantages:

[0017] The present application provides a laser nitriding-hot isostatic pressing treatment method for a titanium alloy surface, which sequentially performs laser nitriding treatment and hot isostatic pressing on the titanium alloy surface to complete the treatment of the titanium alloy. First, a cermet nitriding layer is prepared on the titanium alloy surface through laser nitriding treatment, which improves the strength of the titanium alloy; then, the hot isostatic pressing is performed to eliminate internal defects and improve the uniformity of the structure; the laser nitriding treatment and the hot isostatic pressing are two steps to realize the simultaneous improvement of the strength and toughness of the titanium alloy material and the tribological performance. The treatment method provided by the present application has simple process and strong practicability.

[0018] The treatment method provided by the present application can improve the strength of the titanium alloy through the precipitated TiN ceramic phase, and the hardness of the titanium alloy after treatment is improved by 60Hv, and at the same time, the plasticity and toughness and the friction performance are also improved, the friction coefficient at room temperature is reduced from 1.3 to 1.07, the wear rate is reduced from 9.7*10 -5 mm 3 / (N·m) to 7.8*10 -5 mm 3 / (N·m); the wear rate at 500 ℃ is significantly reduced from 6.9*10 - 5 mm 3 / (N·m) to 1.9*10 -5mm 3 (N·m). BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 XRD patterns (Intensity) of Cermetlayer and Cermetlayer-HIP prepared in Example 1;

[0020] Figure 2 Hardness comparison chart (Hardness) of Cermetlayer and Cermetlayer-HIP prepared in Example 1;

[0021] Figure 3 Indentation morphology comparison chart of Cermetlayer and Cermetlayer-HIP prepared in Example 1 under electron microscope observation, wherein (a) is the indentation morphology chart of Cermetlayer, and (b) is the indentation morphology chart of Cermetlayer-HIP;

[0022] Figure 4 Friction performance comparison chart of Cermetlayer and Cermetlayer-HIP prepared in Example 1, wherein (a) is the friction coefficient comparison chart of Cermetlayer and Cermetlayer-HIP at room temperature and 500℃, and (b) is the wear rate comparison chart of Cermetlayer and Cermetlayer-HIP at room temperature and 500℃ (Temperature, Coefficient of friction, Wear rate). DETAILED DESCRIPTION

[0023] The present application provides a laser nitriding-hipping method for titanium alloy surface, comprising the following steps:

[0024] The laser nitriding treatment and the hot isostatic pressing are sequentially performed on the titanium alloy surface, and the treatment of the titanium alloy is completed.

[0025] In the present application, the titanium alloy is preferably α+β type Ti6Al4V alloy, Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd, Ti-5.5Al-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si-0.2Gd, Ti-5.5Al-3.5Sn-3Zr-1Mo-1Nb-0.3Si, Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y.

[0026] In the present application, the surface of the titanium alloy is preferably polished and repeatedly cleaned before the laser nitriding treatment.

[0027] In the present application, the laser nitriding treatment is carried out by using a fiber laser equipped with a six-axis robot, which is purchased from KUKA Company in Germany, and the fiber laser is purchased from IPG Company in Germany, and the model is YLS-4000.

[0028] In the present application, the laser nitriding treatment is carried out in a nitrogen atmosphere; the input flow of the nitrogen is preferably 5-10 L / min, further preferably 6-9 L / min, and more preferably 7-8 L / min.

[0029] In the present application, the nitrogen is used for participating in the reaction to prepare the cermet nitriding layer, and is used as a protective gas to ensure the smooth progress of the laser nitriding treatment.

[0030] In the present application, the laser output power of the laser nitriding treatment is preferably 1500-2500 W, further preferably 1800-2200 W, and more preferably 2000 W.

[0031] In the present application, the light beam of the laser nitriding treatment is preferably a non-defocusing Gaussian light beam profile.

[0032] In the present application, the spot diameter of the laser nitriding treatment is preferably 2-6 mm, further preferably 3-5 mm, and more preferably 4 mm.

[0033] In the present application, the distance between the nozzle and the substrate of the laser nitriding treatment is preferably 2-10 mm, further preferably 4-8 mm, and more preferably 5-7 mm.

[0034] In the present application, the scanning speed of the laser nitriding treatment is preferably 0.01-0.1 m / min, further preferably 0.03-0.08 m / min, and more preferably 0.05-0.06 m / min.

[0035] In the present application, the temperature rising speed of the hot isostatic pressing is preferably 5-10 ℃ / min, further preferably 6-9 ℃ / min, and more preferably 7-8 ℃ / min.

[0036] In the present application, the target temperature of the hot isostatic pressing is preferably 900-1100 ℃, further preferably 950-1050 ℃, and more preferably 1000 ℃.

[0037] In the present application, the heat preservation and pressure maintaining treatment are carried out simultaneously after reaching the target temperature.

[0038] In the present application, the heat preservation time of the hot isostatic pressing is preferably 2-4 h, further preferably 2.5-3.5 h, and more preferably 3 h.

[0039] In the present application, the pressure holding pressure of the hot isostatic pressing is preferably 120-150 MPa, further preferably 130-140 MPa, and more preferably 135 MPa.

[0040] In the present application, the titanium alloy is treated after the hot isostatic pressing and furnace cooling.

[0041] In the present application, the titanium alloy can be applied to a titanium alloy steam turbine blade, a titanium alloy medical device, a titanium bone, a titanium alloy tank track, and a titanium alloy stirrer, etc. after the treatment.

[0042] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0043] Example 1

[0044] After polishing and repeatedly cleaning the surface of the α+β type Ti6Al4V alloy (Baoji Titanium Industry Group Co., Ltd., China), a fiber laser of a six-axis linkage robot was used to perform laser nitriding treatment on the surface, the input flow of nitrogen was set to 8 L / min, the output power of the laser was set to 2000 W, the beam was a non-defocusing Gaussian beam profile, the spot diameter was 4 mm, the distance between the nozzle and the substrate was 3 mm, and the scanning speed was 0.05 m / min, thereby obtaining the titanium alloy after laser nitriding treatment, which was marked as Cermetlayer.

[0045] Then, the hot isostatic pressing post-treatment was performed, the pressure holding pressure was set to 135 MPa, the temperature rising speed was set to 8 ℃ / min, the temperature was kept at 1000 ℃ for 3 h, and finally the furnace cooling was performed, thereby completing the treatment of the titanium alloy, and the obtained sample was marked as Cermetlayer-HIP.

[0046] The Cermetlayer and the Cermetlayer-HIP obtained in the present example were characterized by XRD, and the XRD patterns of the Cermetlayer and the Cermetlayer-HIP were obtained, as shown in Figure 1 It can be observed from the figure that the modified layer is composed of TiN (FCC) phase and α / α'-Ti (HCP) phase, the modified layer after the hot isostatic pressing post-treatment is composed of TiN (FCC) phase, α / α'-Ti (HCP) phase, β (FCC) phase and TiN (tetrahedron) phase, the RD results determine that the precipitated particles are TiN (tetrahedron) phase and β (FCC) phase, the internal defects of the titanium alloy are reduced, the diffraction peaks after the hot isostatic pressing post-treatment are narrowed as a whole, indicating that the crystallinity is increased and the strain is reduced.

[0047] Hardness tests were performed on the Cermetlayer and Cermetlayer-HIP obtained in this embodiment, and a hardness comparison chart of Cermetlayer and Cermetlayer-HIP was obtained, as shown below. Figure 2 As shown in the figure; from the figure, we can obtain that the hardness of Cermetlayer is 848 HV. 0.5 The hardness of Cermetlayer-HIP is 908 HV. 0.5 After hot isostatic pressing, the hardness of the titanium alloy was significantly improved.

[0048] Indentation tests were performed on the Cermetlayer and Cermetlayer-HIP obtained in this embodiment, and comparison images of the indentation morphology of Cermetlayer and Cermetlayer-HIP under electron microscopy were obtained, as shown in the figure. Figure 3 As shown in the figures, (a) is the indentation morphology of Cermetlayer, and (b) is the indentation morphology of Cermetlayer-HIP. It can be observed from the figures that the ductility and toughness of the titanium alloy are improved after hot isostatic pressing.

[0049] The Cermetlayer and Cermetlayer-HIP obtained in this embodiment were subjected to tribological property tests at room temperature and 500°C, respectively, and a comparison chart of the tribological properties of Cermetlayer and Cermetlayer-HIP was obtained, as shown in the figure. Figure 4 As shown in the figure, (a) is a comparison of the friction coefficients of Cermetlayer and Cermetlayer-HIP, and (b) is a comparison of the wear rates of Cermetlayer and Cermetlayer-HIP. It can be seen from the figures that after hot isostatic pressing, the friction coefficient of the titanium alloy at room temperature decreased from 1.3 to 1.07, and the wear rate decreased from 9.7 × 10⁻⁶. -5 mm 3 / (Nm) decreased to 7.8*10 -5 mm 3 / (N·m), the wear rate at 500℃ is 6.9*10 -5 mm 3 / (N·m) decreased significantly to 1.9*10 -5 mm 3 / (N·m).

[0050] Example 2

[0051] After polishing and repeatedly cleaning the surface of Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd alloy, the fiber laser of the robot equipped with six-axis linkage is used to perform laser nitriding treatment on the surface of the alloy, the input flow of nitrogen is set to 6 L / min, the output power of the laser is set to 1800 W, the beam is a non-defocusing Gaussian beam profile, the spot diameter is 3 mm, the distance between the nozzle and the substrate is 7 mm, and the scanning speed is 0.06 m / min; then, the heat isostatic pressing post-treatment is performed, the pressure holding pressure is set to 130 MPa, the temperature rising speed is set to 7 ℃ / min, the temperature is kept at 900 ℃ for 4 h after reaching 900 ℃, and finally the alloy is cooled in the furnace to complete the treatment of the titanium alloy.

[0052] The same method as in Example 1 is used to test the hardness and tribological properties of the sample treated in this example, and the hardness of the sample is 905 HV 0.5 , the friction coefficient at room temperature is 1.09, the wear rate is 8.0*10 -5 mm 3 / (N·m), and the wear rate at 500 ℃ is 2.1*10 -5 mm 3 / (N·m).

[0053] Example 3

[0054] After polishing and repeatedly cleaning the surface of Ti-5.5Al-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si-0.2Gd alloy, the fiber laser of the robot equipped with six-axis linkage is used to perform laser nitriding treatment on the surface of the alloy, the input flow of nitrogen is set to 10 L / min, the output power of the laser is set to 2200 W, the beam is a non-defocusing Gaussian beam profile, the spot diameter is 5 mm, the distance between the nozzle and the substrate is 5 mm, and the scanning speed is 0.10 m / min; then, the heat isostatic pressing post-treatment is performed, the pressure holding pressure is set to 120 MPa, the temperature rising speed is set to 5 ℃ / min, the temperature is kept at 1100 ℃ for 2 h after reaching 1100 ℃, and finally the alloy is cooled in the furnace to complete the treatment of the titanium alloy.

[0055] The same method as in Example 1 is used to test the hardness and tribological properties of the sample treated in this example, and the hardness of the sample is 907 HV 0.5 , the friction coefficient at room temperature is 1.10, the wear rate is 8.2*10 -5 mm 3 / (N·m), and the wear rate at 500 ℃ is 2.3*10 -5 mm 3 / (N·m).

[0056] From the above examples, the application provides a laser nitriding- hot isostatic pressing treatment method for the surface of a titanium alloy, the precipitated TiN ceramic phase can improve the strength of the titanium alloy, the hardness of the titanium alloy after treatment is increased by 60Hv, at the same time, the plasticity and toughness and the friction performance are also improved, the friction coefficient at room temperature is reduced from 1.3 to 1.07, the wear rate is reduced from 9.7*10 -5 mm 3 / (N·m) to 7.8*10 -5 mm 3 / (N·m); the wear rate at 500 DEG C is significantly reduced from 6.9*10 -5 mm 3 / (N·m) to 1.9*10 - 5 mm 3 / (N·m).

[0057] The above only describes the preferred embodiments of the application, it should be noted that for those skilled in the art, without departing from the principles of the application, a number of improvements and refinements can also be made, these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method of laser nitriding-hot isostatic pressing of a titanium alloy surface, characterized in that, The method comprises the following steps: sequentially performing laser nitriding treatment and hot isostatic pressing on the surface of the titanium alloy to complete the treatment of the titanium alloy; the temperature rising speed of the hot isostatic pressing is 5-10 ℃ / min; the pressure holding pressure of the hot isostatic pressing is 120-150 MPa; the target temperature of the hot isostatic pressing is 900-1100 ℃; the holding time of the hot isostatic pressing is 2-4 h; the titanium alloy is α+β type Ti-6Al-4V alloy, Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd, Ti-5.5Al-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si-0.2Gd, Ti-5.5Al-3.5Sn-3Zr-1Mo-1Nb-0.3Si, Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y.

2. The treatment method of claim 1, wherein, the laser nitriding treatment is performed under a nitrogen atmosphere; the input flow of the nitrogen is 5-10 L / min.

3. The treatment method of claim 1, wherein the laser output power of the laser nitriding treatment is 1500-2500 W.

4. The treatment method of claim 1, wherein the spot diameter of the laser nitriding treatment is 2-6 mm.

5. The treatment method of claim 1, wherein the distance between the nozzle and the substrate of the laser nitriding treatment is 2-10 mm.

6. The treatment method of claim 1, wherein the scanning speed of the laser nitriding treatment is 0.01-0.1 m / min.

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