Process for improving wear resistance of laser cladding titanium alloy coating by using nitrogen as protective gas

Abstract

The application is a process for improving the wear resistance of laser cladding titanium alloy coating by using nitrogen as protective gas, using titanium alloy powder or titanium alloy composite alloy powder without any hard particles as the raw material of laser cladding alloy, by adjusting the process parameters of laser cladding equipment, laser parameters and powder feeding gas, using nitrogen as protective gas, laser cladding is carried out on ALPHA titanium alloy, NEAR-ALPHA titanium alloy and ALPHA-BETA titanium alloy substrate without Sn, Pd and Ru, and laser cladding titanium alloy cladding layer is obtained. The raw material powder of the laser cladding alloy of the application is titanium alloy powder without hard particles or hard phase, by controlling the material and process technology, laser cladding is carried out by using nitrogen as protective gas, and titanium alloy cladding layer is obtained on the surface of the titanium alloy substrate, and the hardness and wear resistance are significantly higher than that of the titanium alloy cladding layer laser cladded by using argon as protective gas under the same material process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser cladding, and in particular to a process for improving the wear resistance of laser cladding titanium alloy coating by using nitrogen as a protective gas. BACKGROUND

[0002] Among industrial application metal materials, titanium alloy has the advantages of low density, high specific strength, good corrosion resistance, etc., and is widely valued and applied in the fields of aerospace, national defense industry, automobile, medical treatment, marine engineering, etc. However, the poor wear resistance of titanium alloy limits its application in some fields.

[0003] In order to improve the wear resistance of titanium alloy workpieces, one of the main methods for improving the service life of workpieces subjected to wear at present is to use laser cladding process to clad a composite alloy wear-resistant layer on the worn surface of the workpiece by using argon as a protective gas.

[0004] In order to improve the wear resistance of titanium alloy workpieces, many studies focus on uniformly mixing tungsten carbide, titanium carbide or boron carbide and metal alloy powder as laser cladding materials, and performing laser cladding under argon protection to obtain a metal matrix composite material composed of high-hardness particles and alloy matrix as a laser cladding wear-resistant layer, such as WC+NiCrBSi alloy, WC+Inconel625 alloy, SiC+NiCrBSi alloy, TiC+NICrBSi alloy, etc. These are mostly laser cladding metal matrix composite cladding layers using hard particles (including carbides or hard ceramic particles) as strengthening phases. This type of laser cladding composite metal material wear-resistant coating requires good compatibility between carbides or hard ceramic hard particles and the matrix metal of the cladding layer in order to better combine and ensure that hard particles do not peel off during wear, especially abrasive wear, thus limiting its application. SUMMARY

[0005] The present application aims to solve the problems of the prior art and provides a process for improving the wear resistance of laser cladding titanium alloy coating by using nitrogen as a protective gas, characterized in that no hard particles are added to the laser cladding alloy, nitrogen is used as a protective gas instead of the conventional argon used as a protective gas, titanium alloy powder is used as cladding material, and laser cladding is performed, and the hardness and wear resistance of the cladding layer are significantly higher than those of laser cladding titanium alloy coating using argon as a protective gas under the same cladding material process.

[0006] To achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0007] The process for improving the wear resistance of laser cladding titanium alloy coating by using nitrogen as protective gas, using titanium alloy powder or titanium alloy composite alloy powder without any hard particles as the laser cladding alloy raw material, by adjusting the process parameters of laser cladding equipment, laser parameters, and powder feeding gas, using nitrogen as protective gas, laser cladding is carried out on ALPHA titanium alloy, NEAR-ALPHA titanium alloy and ALPHA-BETA titanium alloy substrates without Sn, Pd and Ru, and laser cladding titanium alloy cladding layer is obtained.

[0008] The first type of laser cladding alloy raw material is a titanium alloy powder with a Ti content of not less than 80 wt.%, specifically:

[0009] A spherical titanium alloy powder containing alloying elements Al: 3.0 wt.%-7.0 wt.%, V: 3.0 wt.%-5.0 wt.%, Mo: ≤5.0 wt.%, Zr ≤5.0 wt.%, total amount of other elements less than 0.5 wt.%, and impurity element S content less than 0.01 wt.%, and Ti content not less than 80 wt.%; the particle size of the spherical titanium alloy powder in the range of 45-150 μm conforms to the normal distribution of spherical alloy powder.

[0010] The second type of laser cladding alloy raw material is a titanium alloy composite alloy powder composed of a spherical titanium alloy powder with a Ti content of not less than 85 wt.% and elemental Mo powder, specifically:

[0011] A titanium alloy composite alloy powder containing alloying elements Al: 3.0 wt.%-7.0 wt.%, V: 2.0 wt.%-5.0 wt.%, total amount of other elements less than 0.5 wt.%, and impurity element S content less than 0.01 wt.%, and Ti content not less than 85 wt.%, and a pure Mo powder uniformly mixed with a spherical titanium alloy powder with a particle size in the range of 45-150 μm conforming to the normal distribution;

[0012] The addition amount of the pure Mo powder is in the range of 3-6 wt.%; the particle size of the pure Mo powder is 10-55 μm; the molybdenum content of the pure Mo powder is not less than 99 wt.%.

[0013] The process for improving the wear resistance of laser cladding titanium alloy coating by using nitrogen as protective gas, specifically comprising the following steps:

[0014] S1, laser cladding alloy raw material preparation:

[0015] Prepare the laser cladding alloy raw material according to the set requirements. For composite titanium alloy powder and composite alloy powder, mix the powder according to the set ratio and mix it uniformly with a powder mixer. Dry the laser cladding alloy raw material before use;

[0016] S2. Clean the surface of the workpiece where laser cladding is required:

[0017] Degreasing and removing surface pollutants. The surface roughness of the substrate to be clad should be lower than Ra12.6. When the room temperature is lower than 15°C, the substrate needs to be preheated before cladding at a temperature of 150°C.

[0018] S3, Laser Cladding:

[0019] Adjust relevant parameters before cladding begins: adjust the distance between the laser head nozzle and the surface to be clad, and adjust the size and uniformity of the laser spot on the workpiece surface;

[0020] Set the powder feeding rate;

[0021] Set the powder feeding gas pressure-flow;

[0022] Set the shielding gas pressure-flow;

[0023] Set the laser scanning speed;

[0024] Set the laser power according to the required laser energy density;

[0025] Set the overlap width between laser cladding passes;

[0026] Operate the controller-robot for laser cladding;

[0027] S4. Post-processing of laser cladding:

[0028] The surface of the laser cladding layer is ground as required.

[0029] Laser cladding is performed using a multimode continuous wave fiber laser with a power of not less than 4kW and a coaxial powder feeding laser head.

[0030] A rotary table quantitative-pneumatic powder feeder is used to transport the laser cladding alloy raw materials, and argon with a purity higher than 99.9% is used as the powder feeding gas.

[0031] The nitrogen used in the shielding gas is high-purity nitrogen with a nitrogen content higher than 99.99% and an oxygen content lower than 0.01%.

[0032] The beneficial effects of the present invention are as follows: in the present invention, the raw material powder of the laser cladding alloy is a titanium alloy powder without hard particles or hard phases. By controlling materials and process technology, nitrogen is used as a protective gas instead of the conventionally used argon as a protective gas to perform laser cladding, and a titanium alloy cladding layer is obtained on the surface of the titanium alloy substrate. The hardness and wear resistance of the titanium alloy cladding layer are significantly higher than those of the titanium alloy cladding layer obtained by laser cladding using argon as a protective gas using the same material process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Attachment Figure 1The photograph of the titanium alloy laser cladding sample TA with argon as the protective gas in the embodiment 1 of the present application;

[0034] The photograph of the titanium alloy laser cladding sample TN with nitrogen as the protective gas in the embodiment 1 of the present application; Figure 2 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0035] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 3 The metallographic photograph of the cross section of the laser cladding layer of the titanium alloy laser cladding sample TA with argon as the protective gas in the embodiment 1 of the present application under the observation of the optical metallographic microscope with 200 times magnification;

[0036] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 4 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0037] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 5 The metallographic photograph of the cross section of the laser cladding layer of the titanium alloy laser cladding sample TN with nitrogen as the protective gas in the embodiment 1 of the present application under the observation of the optical metallographic microscope with 200 times magnification;

[0038] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 6 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0039] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 7 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0040] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 8 The metallographic photograph of the cross section of the laser cladding layer of the titanium alloy laser cladding sample TMA with argon as the protective gas in the embodiment 2 of the present application under the observation of the optical metallographic microscope with 200 times magnification;

[0041] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 9 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0042] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 10 The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105;

[0043] The photograph of the worn sample after the wet sand-gum wheel abrasive wear test of the samples TA and TN in the embodiment 1 of the present application according to the standard of ASTM G105; Figure 11The microhardness test photo of the titanium alloy composite alloy powder laser cladding sample TMN in the embodiment 2 of the present application with nitrogen as the protective gas;

[0044] The Figure 12 The microhardness test photo of the titanium alloy composite alloy powder laser cladding sample TMN in the embodiment 2 of the present application with nitrogen as the protective gas Figure 11 The microhardness test photo of the titanium alloy composite alloy powder laser cladding sample TMN in the embodiment 2 of the present application with nitrogen as the protective gas

[0045] The Figure 13 The microhardness test photo of the titanium alloy composite alloy powder laser cladding sample TMN in the embodiment 2 of the present application with nitrogen as the protective gas

[0046] The principles and features of the present application will be described in detail below with reference to the accompanying drawings. DETAILED DESCRIPTION

[0047] The principles and features of the present application will be described in detail below with reference to the accompanying drawings.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this description, the singular forms "a", "an" and "the" include plural references unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items.

[0049] The principles and features of the present application will be described in detail below with reference to the accompanying drawings.

[0050] The process for improving the wear resistance of laser cladding titanium alloy coating with nitrogen as the protective gas uses titanium alloy powder or titanium alloy composite alloy powder without any hard particles as the laser cladding alloy raw material, adjusts and controls the process parameters of the laser cladding equipment, laser parameters and powder feeding gas, uses nitrogen as the protective gas, and performs laser cladding on ALPHA (α) titanium alloy, NEAR-ALPHA (near-α) titanium alloy and ALPHA-BETA (α-β) titanium alloy substrates without Sn, Pd and Ru, to obtain a laser cladding titanium alloy cladding layer with a hardness higher than 54HRC.

[0051] The first type of laser cladding alloy raw material is titanium alloy powder with a mass fraction of Ti not less than 80%, specifically: The first type of laser cladding alloy raw material is titanium alloy powder with a mass fraction of Ti not less than 80%, specifically:

[0052] A spherical titanium alloy powder containing alloying elements Al content of 3.0%-7.0% by mass, V content of 3.0%-5.0% by mass, Mo content of ≤5.0% by mass, Zr content of ≤5.0% by mass, total content of other elements less than 0.5% by mass, content of impurity element S less than 0.01% by mass, and Ti content of not less than 80% by mass; the particle size of the spherical titanium alloy powder is in the range of 45-150 mu m, which is a spherical alloy powder conforming to normal distribution.

[0053] The second type of laser cladding alloy raw material is a titanium alloy composite alloy powder composed of a spherical titanium alloy powder with Ti content of not less than 85% by mass and elemental Mo powder, specifically:

[0054] A titanium alloy composite alloy powder obtained by uniformly mixing a spherical titanium alloy powder containing alloying elements Al content of 3.0%-7.0% by mass, V content of 2.0%-5.0% by mass, total content of other elements less than 0.5% by mass, content of impurity element S less than 0.01% by mass, and Ti content of not less than 85% by mass, and a particle size in the range of 45-150 mu m conforming to normal distribution, and a pure Mo powder;

[0055] In the titanium alloy composite alloy powder, the mass proportion of the spherical titanium alloy powder is 94.0%-97.0%;

[0056] In the titanium alloy composite alloy powder, the mass proportion of the pure Mo powder is 3.0%-6.0%; the particle size of the pure Mo powder is 10-55 mu m; the Mo content of the pure Mo powder is not less than 99% by mass.

[0057] A selected laser cladding alloy powder, a continuous wave fiber laser with a power of not less than 4 kW, a rotary quantitative-pneumatic conveying powder feeder, a coaxial powder feeding laser head, and an ABB 6-axis robot form a linkage laser cladding system, nitrogen is used as the protective gas, laser cladding is performed on ALPHA (alpha) titanium alloy, NEAR-ALPHA (near-alpha) titanium alloy, and ALPHA-BETA (alpha-beta) titanium alloy substrates without Sn, Pd, and Ru, and a laser cladding titanium alloy cladding layer with a hardness of 50 HRC or more and good wear resistance is obtained.

[0058] The laser cladding is performed by using a multimode continuous wave fiber laser with a power of not less than 4 kW, a laser wavelength of 1070 nm and a coaxial powder feeding laser head; a positive defocus is selected during the laser cladding, and the spot diameter on the cladding surface is 3 mm; the laser cladding alloy raw material is fed by using a rotary table quantitative-pneumatic conveying powder feeder, argon with a purity of more than 99.9% is used as the powder feeding gas, and the distance from the powder feeding powder intersection point to the cladding surface is 1±0.2 mm; the nitrogen gas used as the protective gas is high-purity nitrogen gas, the nitrogen content is higher than 99.99%, and the oxygen content is lower than 0.01%. The diameter of the laser head nozzle outlet is 8 mm, and the flow of the protective gas nitrogen is 29 L / min-32 L / min.

[0059] The specific steps are as follows:

[0060] S1, laser cladding alloy raw material preparation:

[0061] The laser cladding alloy raw material is prepared according to the set requirements; for the titanium alloy composite alloy powder as the laser cladding alloy material, the mixed powder is prepared according to the set ratio, and the JHT20 double-movement powder mixer is used to uniformly mix the prepared titanium alloy composite alloy powder;

[0062] The laser cladding alloy raw material titanium alloy powder or titanium alloy composite alloy powder needs to be dried before use;

[0063] S2, surface cleaning of the part on the workpiece to be laser cladded:

[0064] The part (base material) on the workpiece to be laser cladded is surface cleaned: oil is removed, any surface contaminants are removed, and the rough base material surface is polished as necessary, so that the surface roughness is lower than Ra6.3. When the room temperature is lower than 15℃, the base material needs to be preheated before cladding, and the preheating temperature is 150℃;

[0065] S3, laser cladding:

[0066] The laser cladding is performed by using a multimode continuous wave fiber laser with a power of not less than 4 kW, a laser wavelength of 1070 nm and a coaxial powder feeding laser head; a positive defocus is selected during the laser cladding, and the spot diameter on the cladding surface is 3 mm; the laser cladding alloy raw material is fed by using a rotary table quantitative-pneumatic conveying powder feeder, argon with a purity of more than 99.9% is used as the powder feeding gas, and the distance from the powder feeding powder intersection point to the cladding surface is 1±0.2 mm; the nitrogen gas used as the protective gas is high-purity nitrogen gas, the nitrogen content is higher than 99.99%, and the oxygen content is lower than 0.01%. The diameter of the laser head nozzle outlet is 8 mm, and the flow of the protective gas nitrogen is 29 L / min-32 L / min.

[0067] The laser cladding is performed by using a multimode continuous wave fiber laser with a power of not less than 4 kW, a laser wavelength of 1070 nm and a coaxial powder feeding laser head; a positive defocus is selected during the laser cladding, and the spot diameter on the cladding surface is 3 mm; the laser cladding alloy raw material is fed by using a rotary table quantitative-pneumatic conveying powder feeder, argon with a purity of more than 99.9% is used as the powder feeding gas, and the distance from the powder feeding powder intersection point to the cladding surface is 1±0.2 mm; the nitrogen gas used as the protective gas is high-purity nitrogen gas, the nitrogen content is higher than 99.99%, and the oxygen content is lower than 0.01%. The diameter of the laser head nozzle outlet is 8 mm, and the flow of the protective gas nitrogen is 29 L / min-32 L / min.

[0068] The nitrogen gas used as the protective gas is high-purity nitrogen gas, the nitrogen content is higher than 99.99%, and the oxygen content is lower than 0.01%.

[0069] Adjusting the distance between the laser head nozzle and the surface to be cladded, adjusting the defocus distance, adjusting the size and uniformity of the laser spot on the surface of the workpiece before the cladding starts;

[0070] Setting the powder feeding rate;

[0071] Setting the powder feeding pressure-flow rate;

[0072] Setting the protective gas pressure-flow rate;

[0073] Setting the laser scanning speed;

[0074] Setting the laser power according to the required laser energy density;

[0075] Setting the overlay width between the laser cladding passes;

[0076] Operating the controller-robot to perform laser cladding;

[0077] S4, post-laser cladding processing:

[0078] According to the requirements, performing grinding processing on the surface of the laser cladded layer.

[0079] The present application is suitable for laser cladding on the substrate of ALPHA (alpha) titanium alloy, NEAR-ALPHA (near-alpha) titanium alloy and ALPHA-BETA (alpha-beta) titanium alloy without Sn, Pd and Ru.

[0080] The wear-resistant alloy layer on the surface of the titanium alloy cladded by laser according to the present application has the following characteristics:

[0081] (1) The metallographic observation shows that there are hard phases dispersedly distributed in the form of dendrites in the laser cladded alloy layer cladded by laser with nitrogen as the protective gas.

[0082] (2) The SEM-EDS observation analysis combined with XRD analysis shows that the dendritic phase is titanium nitride.

[0083] (3) On the titanium alloy substrate with a hardness of 30±3HRC, the hardness of the alloy layer cladded by laser with nitrogen as the protective gas is 53HRC-57HRC, which is significantly higher than that of the case with argon as the protective gas under the same process material.

[0084] (4) The wet sand-rubber wheel abrasive wear test result according to the standard of ASTM G105 shows that the wear amount of the cladded layer cladded by laser with nitrogen as the protective gas according to the present application is less than 1 / 2 of that of the cladded layer cladded by laser with argon as the protective gas. Specific embodiment 1:

[0086] A spherical titanium alloy powder was used as the laser cladding alloy powder, argon gas with a flow rate of 30 L / min was used as the protective gas, and nitrogen gas with a flow rate of 30 L / min was used as the protective gas, and the laser cladding samples TA and TN were prepared by the above laser cladding steps. The wet sand-dry rubber abrasive wear test was carried out on the samples TA and TN according to the standard of ASTM G105, the hardness test of the cladding layer was carried out by using HR-150A Rockwell hardness tester, the microstructure observation was carried out by using DP-TOP optical microscope, and the microhardness test was carried out by using WS-ATM+CCD type microhardness tester, so as to investigate the change of the performance of the laser cladding layer obtained by replacing argon gas with nitrogen gas as the protective gas for titanium alloy laser cladding.

[0087] The specific operation is as follows:

[0088] The alloy powder for laser cladding: the spherical titanium alloy powder with the composition listed in Table 1 was used as the alloy powder for laser cladding. The particle size of the powder was in the range of 45 μm-100 μm; the apparent density was 2.49 g / cm 3 .

[0089] Table 1

[0090]

[0091] The substrate material: Ti-6Al-4V-4Mo titanium alloy; size: 90 mm long x 40 mm wide x 15 mm thick.

[0092] Laser cladding equipment-process parameters:

[0093] A 6-kilowatt multi-mode continuous wave fiber laser was used, with a laser wavelength of 1070 nm, and a power of 3750 W was selected;

[0094] A cohesive-reflection output-coaxial powder feeding laser head was used;

[0095] The spot size was 3 mm;

[0096] A rotary quantitative-pneumatic conveying powder feeder was used, and argon gas with a purity higher than 99.9% was used as the powder feeding gas, and the powder feeding gas flow rate was 25 L / min;

[0097] Protective gas: argon gas was used as the protective gas for laser cladding of sample TA and nitrogen gas was used as the protective gas for laser cladding of sample TN:

[0098] The purity of the argon gas used as the protective gas for laser cladding of sample TA was higher than 99.9%, and the flow rate of the protective gas argon was 30 L / min;

[0099] The high-purity nitrogen gas with a nitrogen content higher than 99.99% and an oxygen content lower than 0.01% was used as the protective gas for laser cladding of sample TN, and the flow rate of the protective gas nitrogen was 30 L / min.

[0100] Laser cladding was carried out along the length direction of the sample substrate, with an overlap width of 1 mm. Laser cladding samples TA and TN were respectively carried out on the substrate of TI-6Al-4V-4Mo titanium alloy. Figure 1 The photos of laser cladding samples TA and TN are shown.

[0101] In order to investigate the influence of using nitrogen as protective gas for titanium alloy laser cladding instead of the commonly used argon as protective gas for titanium alloy laser cladding on the performance of the laser cladding layer, the following performance tests were carried out:

[0102] (1) Wet sand-gel wheel abrasive wear test was carried out according to ASTM G105 standard;

[0103] The wet sand-gel wheel abrasive wear sample conforming to the requirements of ASTM G105 standard was prepared by cutting, machining and surface grinding on the laser cladding sample. Wet sand-gel wheel abrasive wear test was carried out according to ASTM G105 standard. The mass of the sample before and after abrasive wear was measured by a precision balance with a sensitivity of 0.0001 g, and the mass loss was calculated. The morphology of the worn sample after the wet sand-gel wheel abrasive wear test of sample TA and sample TN according to ASTM G105 standard is shown in the photos, and it can be seen that the depth of the wear groove of sample TA laser cladding with argon as protective gas is obviously higher than that of sample TN laser cladding with nitrogen as protective gas. Table 2 shows the test results of the mass loss of the wet sand-gel wheel abrasive wear test of sample TA and sample TN according to ASTM G105 standard. Figure 2

[0104] Table 2

[0105]

[0106] From the test results in Table 2, it can be seen that the wear of the laser cladding layer of titanium alloy laser cladding with nitrogen as protective gas is obviously lower than that of the laser cladding layer of titanium alloy laser cladding with argon as protective gas. It is shown that using nitrogen as protective gas instead of argon as protective gas for titanium alloy laser cladding can significantly improve the wear resistance of the laser cladding layer.

[0107] (2) Laser cladding layer hardness test was carried out on the laser cladding sample;

[0108] HR-150A Rockwell hardness tester was used to test the hardness of the laser cladding layer of sample TA laser cladded with argon as protective gas and sample TN laser cladded with nitrogen as protective gas, and the test results are shown in Table 3.

[0109] Table 3

[0110] ​

[0111] From the hardness test results, it is seen that the hardness of the laser cladding layer of the titanium alloy cladding sample TN (56HRC ± 1HRC) is higher than that of the laser cladding layer of the titanium alloy cladding sample TA (28HRC ± 1HRC) when nitrogen is used as the protective gas instead of argon. This shows that the use of nitrogen as the protective gas instead of argon can significantly improve the hardness of the laser cladding layer.

[0112] (3) Optical metallographic microscope observation was performed on the laser cladding sample;

[0113] The metallographic photos of the cross section of the laser cladding layer of the laser cladding sample TA observed under the optical metallographic microscope at a magnification of 200 times (attached Figure 3 ) and the metallographic photos of the cross section of the laser cladding layer of the laser cladding sample TN observed under the optical metallographic microscope at a magnification of 200 times (attached Figure 5 ) were compared; it is seen that the metallographic structures of the two are obviously different.

[0114] SEM-EDS observation and analysis combined with XRD phase analysis show that the laser cladding layer obtained by laser cladding with nitrogen as the protective gas contains titanium nitride.

[0115] (4) Microhardness test was performed on the laser cladding sample;

[0116] The WS-ATM+CCD type microhardness tester was used to perform microhardness tests on the laser cladding samples TA and TN, respectively.

[0117] Figure 4 The microhardness test photos of the laser cladding sample TA obtained in the specific embodiment 1 are given; Figure 4 The hardness values of the microhardness measurement points in the photos are listed in Table 4. Table 4 is the microhardness test photo of the laser cladding sample TA obtained by using argon as the protective gas Figure 3 The hardness values of the microhardness measurement points in the photos are listed in Table 4. Table 4 is the microhardness test photo of the laser cladding sample TA obtained by using argon as the protective gas

[0118] Table 4

[0119]

[0120] Figure 6 The microhardness test photos of the laser cladding sample TN obtained in the specific embodiment 1 are given. The hardness values of the microhardness measurement points in the photos are listed in Table 5. Table 5 is the microhardness test photo of the laser cladding sample TN obtained by using nitrogen as the protective gas Figure 6The hardness values of each microhardness measurement point (the WS-ATM+CCD type microhardness meter can simultaneously display the corresponding HRC hardness values).

[0121] Table 5

[0122]

[0123] Comparing the microhardness measurement data listed in Tables 4 and 5, it can be seen that the hardness of the laser cladding layer of the sample TN (643.88 HV, 617.77 HV) is significantly higher than the hardness of the laser cladding layer of the sample TA (362.99 HV, 345.11 HV) when nitrogen is used as the protective gas. This indicates that using nitrogen as the protective gas instead of argon as the protective gas for titanium alloy laser cladding can significantly improve the microhardness of the laser cladding layer.

[0124] From the above test results, it can be seen that using nitrogen as the protective gas instead of argon as the protective gas for titanium alloy laser cladding can significantly improve the hardness and wear resistance of the titanium alloy laser cladding layer. Specific Example 2:

[0126] Specific Example 2 is to use a titanium alloy composite alloy powder of 96 wt.% of spherical titanium alloy powder with the composition listed in Table 1 and 4 wt.% of pure Mo powder uniformly mixed as the laser cladding alloy powder, respectively use argon with a flow rate of 30 L / min as the protective gas and nitrogen with a flow rate of 30 L / min as the protective gas, and perform laser cladding according to the above laser cladding steps to prepare samples TMA and TMN. Then, according to the ASTM G105 standard, the wet sand-gel wheel abrasive wear test is performed on the samples TMA and TMN, the HR-150A Rockwell hardness tester is used for hardness testing of the cladding layer, the DP-TOP optical metallographic microscope is used for microstructure observation, and the WS-ATM+CCD type microhardness tester is used for microhardness testing, to investigate the changes in the performance of the laser cladding layer obtained by using nitrogen instead of argon as the protective gas for titanium alloy laser cladding.

[0127] The specific operation is as follows:

[0128] The alloy powder for laser cladding is a composite alloy powder (hereinafter referred to as titanium alloy composite alloy powder) uniformly mixed with titanium alloy powder and elemental metal powder. Specifically, a composite alloy powder composed of 96% by mass of spherical titanium alloy powder and 4% by mass of pure Mo powder uniformly mixed is used as the alloy powder for laser cladding, wherein: the chemical composition of the 96% by mass of spherical titanium alloy powder is as listed in Table 1, and the particle size of the powder is in the range of 45 μm-100 μm; the apparent density is 2.49 g / cm 3 .

[0129] The pure Mo powder with a mass ratio of 4% is a pure Mo powder with a Mo content of 99.8% and an oxygen content of less than 0.088%, and a particle size in the range of 10 μm-55 μm. The mixed alloy powder prepared according to the mass ratio is uniformly mixed by a JHT20 double-motion powder mixer for 24 hours and is ready for use. The mixed alloy powder needs to be dried before being used in laser cladding.

[0130] Base material: TI-6Al-4V-4Mo titanium alloy; size: 90 mm long x 40 mm wide x 15 mm thick.

[0131] Laser cladding equipment-process parameters:

[0132] A 6-kilowatt multi-mode continuous wave fiber laser is used, and the laser wavelength is 1070 nm, and the power is 3750 W;

[0133] A cohesive-reflection output-coaxial powder feeding laser head is used;

[0134] Spot diameter: 3 mm;

[0135] A rotary table quantitative-pneumatic conveying powder feeder is used, and argon gas with a purity of more than 99.9% is used as the powder feeding gas, and the powder feeding gas flow is 25 L / min;

[0136] Protective gas: argon gas is used as the protective gas for laser cladding sample TMA, and nitrogen gas is used as the protective gas for laser cladding sample TMN:

[0137] The purity of the argon gas used as the protective gas for laser cladding sample TMA is more than 99.9%, and the protective gas argon flow is 30 L / min;

[0138] High-purity nitrogen gas with a nitrogen content of more than 99.99% and an oxygen content of less than 0.01% is used as the protective gas for laser cladding sample TMN, and the protective gas nitrogen flow is 30 L / min.

[0139] Laser cladding is performed along the length direction of the sample base, and the lap width is 1 mm. Argon gas is used as the protective gas for laser cladding sample TMA, and nitrogen gas is used as the protective gas for laser cladding sample TMN on the TI-6Al-4V-4Mo titanium alloy base.

[0140] In order to investigate the influence of using nitrogen gas as the protective gas for titanium alloy composite alloy powder laser cladding instead of the commonly used argon gas as the protective gas for titanium alloy composite alloy powder laser cladding on the performance of the laser cladding layer, the following performance tests are performed:

[0141] (1) Wet sand-pneumatic abrasive wear test according to ASTM G105 standard;

[0142] The wet sand rubber wheel abrasion test samples were made by cutting-machining-surface grinding the laser cladding samples according to the standard of ASTM G105. The wet sand rubber wheel abrasion test was carried out according to the standard of ASTM G105. The mass of the test sample before and after the abrasion test was measured by a precision balance with a sensitivity of 0.0001 g, and the mass loss of the test sample was calculated. Figure 7 The photos of the worn surfaces of the test sample TMA and the test sample TMN after the wet sand rubber wheel abrasion test according to the standard of ASTM G105 are shown. It can be seen that the depth of the wear groove of the test sample TMA laser cladded with argon as the shielding gas is obviously higher than that of the test sample TMN laser cladded with nitrogen as the shielding gas. The test results of the wet sand rubber wheel abrasion test of the test sample TMA and the test sample TMN according to the standard of ASTM G105 are shown in Table 6.

[0143] Table 6

[0144]

[0145] It can be seen from the test results in Table 6 that the mass loss of the laser cladded layer of the test sample TMN laser cladded with titanium alloy composite alloy powder with nitrogen as the shielding gas is obviously lower than that of the test sample TMA laser cladded with titanium alloy composite alloy powder with argon as the shielding gas. It is shown that the laser cladding of titanium alloy composite alloy powder with nitrogen as the shielding gas instead of argon as the shielding gas can significantly improve the wear resistance of the laser cladded layer.

[0146] (2) The hardness test of the laser cladded layer of the laser cladded sample was carried out;

[0147] The hardness test of the laser cladded layer of the test sample TMA laser cladded with titanium alloy composite alloy powder with argon as the shielding gas and the test sample TMN laser cladded with titanium alloy composite alloy powder with nitrogen as the shielding gas was carried out by using a HR-150A Rockwell hardness tester, and the test results are shown in Table 7.

[0148] Table 7

[0149]

[0150] It can be seen from the hardness test results that the hardness of the laser cladded layer of the test sample TNN laser cladded with titanium alloy composite alloy powder with nitrogen as the shielding gas (55.5 HRC ± 1 HRC) is higher than that of the test sample TMA laser cladded with titanium alloy composite alloy powder with argon as the shielding gas (39.5 HRC ± 1.5 HRC). It is shown that the laser cladding of titanium alloy composite alloy powder with nitrogen as the shielding gas instead of argon as the shielding gas can significantly improve the hardness of the laser cladded layer.

[0151] (3) The laser cladding sample was observed by optical microscope;

[0152] The metallographic photos of the laser cladding layer cross section of the laser cladding sample TMA with argon as the protective gas were compared with the metallographic photos of the laser cladding layer cross section of the laser cladding sample TMN with nitrogen as the protective gas, which were observed under the optical microscope with 200 times magnification (the metallographic photos of the laser cladding layer cross section of the laser cladding sample TMA with argon as the protective gas are attached in Figure 8 ) and the metallographic photos of the laser cladding layer cross section of the laser cladding sample TMN with nitrogen as the protective gas are attached in Figure 10 ); it was found that the metallographic structures of the two were obviously different. The metallographic structure of the laser cladding layer of the laser cladding sample TMN with nitrogen as the protective gas had obvious dendritic characteristics.

[0153] The SEM-EDS observation analysis combined with XRD phase analysis showed that the laser cladding layer with nitrogen as the protective gas had titanium nitride generated.

[0154] (4) The microhardness test was conducted on the laser cladding sample:

[0155] The microhardness test was conducted on the laser cladding sample TMA and TMN with the WS-ATM+CCD type microhardness tester.

[0156] Figure 9 The microhardness test photos of the laser cladding sample TMA with argon as the protective gas in the specific embodiment 1 are given. The hardness values of the microhardness measurement points in the figure are listed in Table 8. Table 8 is the microhardness test photos corresponding to the laser cladding sample TMA Figure 9 The hardness values of the microhardness measurement points in the figure are listed in Table 8. Table 8 is the microhardness test photos corresponding to the laser cladding sample TMA

[0157] Table 8

[0158]

[0159] Figure 11 The microhardness test photos of the laser cladding sample TMN with nitrogen as the protective gas in the specific embodiment 2 are given. The hardness values of the microhardness measurement points in the figure are listed in Table 9. Table 9 is the microhardness test photos corresponding to the laser cladding sample TMN Figure 11 The hardness values of the microhardness measurement points in the figure are listed in Table 9. Table 9 is the microhardness test photos corresponding to the laser cladding sample TMN

[0160] Table 9

[0161]

[0162] Figure 12 The microhardness test photos of the laser cladding sample TMN with nitrogen as the protective gas in the specific embodiment 2 are given. The hardness values of the microhardness measurement points in the figure are listed in Table 9. Table 9 is the microhardness test photos corresponding to the laser cladding sample TMNFigure 11 Microhardness testing photos of the area. The hardness values of each microhardness measuring point in the figure are listed in Table 10. Table 10 is the microhardness testing photo corresponding to the laser cladding sample TMN Figure 12 The hardness values of each microhardness measuring point in the above figure (the WS-ATM+CCD type microhardness tester can simultaneously display the corresponding HRC hardness values).

[0163] Table 10

[0164]

[0165] Comparing the microhardness measurement data listed in Tables 8, 9 and 10, it can be seen that the hardness of the laser cladding layer of the titanium alloy composite alloy laser cladding sample TMN using nitrogen as the protective gas (615.67HV-6662.03HV) is significantly higher than that of the laser cladding layer of the titanium alloy composite alloy sample TMA using argon as the protective gas (374.52HV, 418.13HV). This indicates that using nitrogen as the protective gas instead of argon as the protective gas for titanium alloy laser cladding can significantly improve the microhardness of the laser cladding layer.

[0166] From the above example test results, it can be seen that using nitrogen as the protective gas instead of argon as the protective gas for titanium alloy composite alloy laser cladding can significantly improve the hardness and wear resistance of the titanium alloy laser cladding layer.

[0167] Figure 8 Figure 13 Figure 9 shows the micro-area SEM-EDS analysis photo of the dendritic structure of the laser cladding layer of the titanium alloy composite alloy powder laser cladding sample TMN in Example 2 of the present application using nitrogen as the protective gas. From the micro-area SEM-EDS composition analysis results of the dendritic structure of the laser cladding layer of the titanium alloy composite alloy powder laser cladding sample TMN using nitrogen as the protective gas, it can be seen that the titanium content of the dendritic structure of the laser cladding layer of the titanium alloy composite alloy powder laser cladding sample TMN is 66.04at.%, and the nitrogen content is 27.21at.%. Combined with the XRD analysis, it is shown that titanium nitride (Ti2N) phase is generated. It is noted that aluminum (3.56 at.%), vanadium (1.71 at.%), and molybdenum (1.47 at.%) are also dissolved in the titanium nitride phase. (The problem of obtaining in-situ endogenous titanium nitride hard phase by titanium alloy laser cladding using nitrogen as the protective gas is not the focus of the present application. The focus of the present application is to use nitrogen as the protective gas instead of argon as the protective gas for titanium alloy laser cladding, which can improve the hardness and wear resistance of the laser cladding layer).

[0168] The test results of the above specific embodiments 1 and 2 show that the laser cladding titanium alloy with nitrogen gas instead of the commonly used argon gas as the protective gas can significantly improve the hardness and the abrasive wear resistance of the laser cladding layer. The hardness of the laser cladding alloy layer with nitrogen gas as the protective gas is above 50HRC, the abrasive wear loss is less than 1 / 2 of the abrasive wear loss of the laser cladding alloy layer with argon gas as the protective gas, and the relative wear resistance is improved by more than 2 times.

[0169] The application is described above with reference to the drawings, and it is obvious that the specific implementation of the application is not limited by the above manner, and various improvements using the method concept and technical scheme of the application or direct application to other occasions without improvement are within the protection scope of the application.

Claims

1. A process for improving the wear resistance of laser cladded titanium alloy coating using nitrogen as a shielding gas, characterized in that, The titanium alloy powder or the titanium alloy composite alloy powder without any hard particles is used as a laser cladding alloy raw material, the process parameters of a laser cladding device, laser parameters and powder feeding gas are regulated, nitrogen is used as a protective gas, laser cladding is performed on an ALPHA titanium alloy, a NEAR-ALPHA titanium alloy and an ALPHA-BETA titanium alloy substrate without Sn, Pd and Ru, and a laser cladding titanium alloy cladding layer is obtained; The laser cladding alloy raw material is a titanium alloy powder with a Ti content of not less than 80 wet.% or a titanium alloy composite alloy powder composed of a spherical titanium alloy powder with a Ti content of not less than 85 wet.% and elemental Mo powder; The titanium alloy powder with a Ti content of not less than 80 wet.% is specifically as follows: The spherical titanium alloy powder contains alloy elements Al: 3.0 wt.%-7.0 wt.%, V: 3.0 wt.%-5.0 wt.%, Mo: ≤5.0 wt.%, Zr ≤5.0 wt.%, other elements with a total content of less than 0.5 wt.%, impurity element S with a content of less than 0.01 wt.% and Ti with a content of not less than 80 wt.%; the particle size of the spherical titanium alloy powder in the range of 45 μm-150 μm is a spherical alloy powder conforming to normal distribution; The laser cladding alloy raw material is a titanium alloy composite alloy powder composed of a spherical titanium alloy powder with a Ti content of not less than 85 wet.% and elemental Mo powder, specifically as follows: The spherical titanium alloy powder contains alloy elements Al: 3.0 wt.%-7.0 wt.%, V: 2.0 wt.%-5.0 wt.%, other elements with a total content of less than 0.5 wt.%, impurity element S with a content of less than 0.01 wt.% and Ti with a content of not less than 85 wt.%, and the particle size of the spherical titanium alloy powder in the range of 45 μm-150 μm conforms to normal distribution; and the titanium alloy composite alloy powder is a uniform mixture of the spherical titanium alloy powder and pure Mo powder; The addition amount of the pure Mo powder ranges from 3 wt.% to 6 wt.%; the particle size of the pure Mo powder is 10 μm-55 μm; and the pure Mo powder contains not less than 99 wt.% of Mo.

2. The process of claim 1, wherein the process is carried out in a nitrogen atmosphere. The specific steps are as follows: S1, preparation of laser cladding alloy raw material: Prepare the laser cladding alloy raw material according to the set requirements; for the composite titanium alloy powder and the composite alloy powder, mix the powders according to the set ratio, mix uniformly with a powder mixer and dry the laser cladding alloy raw material before use; S2, surface cleaning of the part to be laser clad on the workpiece: Remove oil and surface contaminants; the surface roughness of the substrate to be clad is less than Ra12.6; when the room temperature is lower than 15℃, the substrate needs to be preheated before cladding, and the preheating temperature is 150℃; S3, laser cladding: Adjust the distance between the laser head nozzle and the surface to be clad, adjust the size and uniformity of the laser spot on the workpiece surface before cladding starts; Set the powder feeding rate; Set the powder gas pressure-flow rate; Set the protective gas pressure-flow rate; Set the laser scanning speed; Set the laser power according to the required laser energy density; Set the overlap width between laser cladding passes; Operate the controller-robot to perform laser cladding; S4, laser cladding post-processing: According to the requirements, the surface of the laser cladding layer is ground.

3. The process of claim 2, wherein the process is carried out in a nitrogen atmosphere. Use a multimode continuous wave fiber laser with a power not less than 4kW, coaxial powder feeding laser head for laser cladding.

4. The process of claim 3, wherein the process is carried out in a nitrogen atmosphere. Use a rotary table quantitative-pneumatic conveying powder feeder to convey the laser cladding alloy raw materials, and use argon with a purity higher than 99.9% as the powder feeding gas.

5. The process of claim 4, wherein the process is carried out in a nitrogen atmosphere. The nitrogen used as the protective gas is high-purity nitrogen with a nitrogen content higher than 99.99% and an oxygen content lower than 0.01%.

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