High-entropy alloy coating and preparation method and application thereof

Abstract

The invention discloses a high-entropy alloy coating and a preparation method and application thereof.The chemical component of the high-entropy alloy coating is TiNbZrMo, the organization structure of the high-entropy alloy coating is a body-centered cubic solid solution composed of dendrites and cellular crystals, and the high-entropy alloy coating is prepared by mixing Ti powder, Nb powder, Zr powder and Mo powder according to the proportion and then conducting extrusion forming. The high-entropy alloy coating is formed on the surface of the titanium alloy matrix in a cladding mode through a laser cladding method, the high-entropy alloy coating is well combined with the brake disc matrix, the high-entropy alloy brake disc has the advantages of being high in strength and good in wear resistance and thermal fatigue resistance, the comprehensive performance is outstanding, the problem that titanium alloy is poor in wear resistance and high-temperature oxidation resistance can be effectively solved, and the service life of the brake disc is prolonged. The performance and the service life of the titanium alloy brake disc are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-entropy alloy coatings, and in particular, to a high-entropy alloy coating, a preparation method and an application thereof. Background Art

[0002] The lightweight of transportation equipment is beneficial to energy conservation and reduction of vehicle operation energy consumption. Compared with traditional cast iron and steel, titanium alloy has the characteristics of low density and high specific strength, and is a new type of lightweight brake disc material for trains. However, in practical applications, the wear resistance of titanium alloy is poor and it is prone to wear failure. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above deficiencies of the prior art, and to provide a high-entropy alloy coating, a preparation method and an application thereof.

[0004] The present invention solves its technical problems by adopting the following technical solutions.

[0005] An embodiment of the present invention provides a high-entropy alloy coating. The chemical composition of the high-entropy alloy coating is TiNbZrMo, and the microstructure is a body-centered cubic solid solution composed of dendritic crystals and cellular crystals.

[0006] The present invention also provides a preparation method of the above high-entropy alloy coating, which includes: forming the high-entropy alloy coating on the surface of a substrate by laser cladding.

[0007] The present invention also provides an application of the above high-entropy alloy coating. The high-entropy alloy coating is applied to the surface of a titanium alloy brake disc.

[0008] The present invention also provides a titanium alloy brake disc for high-speed trains, which includes a brake disc substrate and a laser cladding layer on the surface of the brake disc. The material of the brake disc substrate is titanium alloy, and the laser cladding layer is prepared by the above preparation method.

[0009] The present invention has the following beneficial effects:

[0010] The present invention provides a high-entropy alloy coating, a preparation method and an application thereof. The chemical composition of the high-entropy alloy coating provided by the present invention is TiNbZrMo, and the microstructure is a body-centered cubic solid solution composed of dendritic crystals and cellular crystals. It is formed by mixing Ti powder, Nb powder, Zr powder and Mo powder in proportion and then laser cladding on the surface of a titanium alloy substrate to form a high-entropy alloy coating. The high-entropy alloy coating has good bonding with the brake disc substrate, and has the characteristics of high strength, good wear resistance and heat fatigue resistance. Its comprehensive performance is outstanding, which can effectively improve the problems of poor wear resistance and high-temperature oxidation resistance of titanium alloy, and improve the performance and service life of the titanium alloy brake disc. Brief Description of the Drawings

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0012] Figure 1 It is the penetrant inspection results and surface forming conditions of the laser cladding coatings obtained in Embodiments 1 - 5, Comparative Examples 3 - 4, and Comparative Example 6 of the present invention, where (a - e) are the penetrant inspection diagrams of Embodiments 1 - 5, (f - g) are the penetrant inspection diagrams of Comparative Examples 3 - 4, and (h) is the surface forming condition of Comparative Example 6;

[0013] Figure 2 It is the microstructural diagram of the coating in Embodiment 2 of the present invention, where (a) is the metallographic diagram of the interface between the coating and the substrate, and (b) is the metallographic structure diagram of the top of the coating;

[0014] Figure 3 It is the vertical - direction micro - hardness change diagram of the coatings in Embodiments 1 - 5 of the present invention;

[0015] Figure 4 It is the friction - coefficient curve of the friction - and - wear experiments on the coatings in Embodiments 1 - 5, Comparative Examples 1 - 2 of the present invention;

[0016] Figure 5 It is the wear - profile diagram after the friction - and - wear experiments on the coatings in Embodiments 4 - 5, Comparative Examples 1 - 2 of the present invention.

[0017] Figure 6 It is the surface morphology of the coatings in Embodiments 1 - 2, Comparative Example 1 of the present invention after 1000 thermal fatigue tests. Detailed Embodiments

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0019] Hereinafter, a high - entropy alloy coating, its preparation method, and application provided by the embodiments of the present invention will be specifically described.

[0020] In the first aspect, the embodiments of the present invention provide a high - entropy alloy coating, the chemical composition of the high - entropy alloy coating is TiNbZrMo, and the microstructure is a body - centered cubic solid solution composed of dendrites and cellular crystals.

[0021] In some optional embodiments, in the high-entropy alloy coating, the atomic ratio of the three elements Ti, Nb, and Zr to the element Mo is 3:(0.1 - 0.5), and among the three elements Ti, Nb, and Zr, the mass proportion of the Ti element is 11.51 - 20.63%, the mass proportion of the Nb element is 40.05 - 44.65%, and the mass proportion of the Zr element is 39.32 - 43.84%.

[0022] In some optional embodiments, the high-entropy alloy coating is a multi-layer structure, with each layer having a thickness of 0.8 - 1 mm and a total thickness of 3.5 - 5 mm.

[0023] In some optional embodiments, the friction coefficient of the high-entropy alloy coating is in the range of 0.28 - 0.44, and the microhardness reaches above 360 Hv.

[0024] In a second aspect, an embodiment of the present invention provides a method for preparing the above-mentioned high-entropy alloy coating, which includes: forming the high-entropy alloy coating on the surface of a substrate by laser cladding.

[0025] In some optional embodiments, it includes the following steps: After drying the composite powder of Ti powder, Nb powder, Zr powder, and Mo powder in a vacuum drying oven at 80 °C for 2 h, it is loaded into a powder feeder, and laser cladding is used to prepare the coating, where: the process parameters of laser cladding are: the cladding speed is 3.0 - 3.5 mm / s, the laser spot diameter is 4 mm, the laser power is 2800 - 3200 W, the coaxial powder feeding method is adopted, the powder feeding speed is 0.8 - 1.0 r / min, and the protective gas flow rate is 25 L / min.

[0026] In some optional embodiments, the laser cladding layer is formed by multi-pass laser cladding, and the overlapping rate between adjacent pass cladding layers is 40% - 50%, and the laser cladding parameters for each pass are the same.

[0027] In some optional embodiments, the preparation method of the mixed powder is as follows: Ti powder, Nb powder, and Zr powder are mixed by high-energy ball milling in proportion, where: the ball milling speed is 150 - 180 r / min, it rotates clockwise and counterclockwise for 30 - 45 min in turn, stands still for 10 min, and repeats 5 cycles;

[0028] Preferably, the four powders are all high-purity spherical powders with a purity of 99.99%, and the powder diameter is 53 - 150 μm.

[0029] In some optional embodiments, it further includes: before laser cladding, grinding and cleaning the surface of the substrate, then preheating it to 300 °C, using argon as the protective gas, performing laser cladding, and maintaining the temperature of the brake disc at 280 °C to 320 °C during the cladding process. After the cladding is completed, perform heat preservation treatment at a temperature of 300 °C to 400 °C for 3 to 4 hours;

[0030] Preferably, after the heat preservation treatment, take out the substrate with the coating, and then perform cold pressing treatment, controlling the deformation amount to be less than ±0.2 mm;

[0031] Preferably, the substrate is a titanium alloy, more preferably a titanium alloy brake disc, and further preferably a titanium alloy brake disc for high-speed trains. The material of the brake disc substrate includes but is not limited to TC4.

[0032] In some optional embodiments, a method for forming a TiNbZr coating on the surface of a titanium alloy brake disc for high-speed trains includes the following steps:

[0033] S1. Load the cladding powder into the powder feeder of the laser cladding device and set it aside.

[0034] S2. Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 to 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 hour, and the preheating temperature is 300 °C.

[0035] S3. Use argon as the protective gas and perform laser cladding. The process parameters are as follows: laser power 2800 to 3200 W, scanning speed 3.0 to 3.5 mm / s, powder feeding speed 0.8 to 1.0 r / min, overlapping rate 50%, and protective gas flow rate 25 L / min.

[0036] S4. Keep the brake disc obtained after cladding at a temperature of 300 to 400 °C for heat preservation treatment for 3 to 4 hours to further reduce the residual stress left by laser cladding.

[0037] S5. Take out the coated brake disc obtained after heat preservation treatment from the tooling to release the stress.

[0038] S6. Perform cold pressing treatment on the taken-out coated brake disc, controlling the deformation amount to be less than ±0.2 mm.

[0039] S7. Perform surface machining on the coated brake disc obtained after cold pressing to ensure that the flatness after turning is Ra0.8.

[0040] The preparation method of the high-entropy alloy coating provided by the embodiments of the present invention can reduce the difference in thermal expansion coefficients between the base material and the cladding material by performing preheating treatment, laser cladding, and post-heat treatment, so as to form a metallurgical bond between the cladding material and the base material. That is, by optimizing the composition and the laser cladding process, the coating formed by the TiNbZrMo composite alloy powder has a high bonding strength with the substrate, and is crack-free, high-strength, high-toughness, and high-performance, which can effectively slow down the wear of the brake disc and extend its service life.

[0041] In the third aspect, the embodiments of the present invention provide an application of the above high-entropy alloy coating, and the high-entropy alloy coating is applied to the surface of a titanium alloy brake disc. After forming the high-entropy alloy coating with the above composition on the surface of the substrate, it can form a good bond with the substrate, has excellent wear resistance, and can meet the performance requirements for long-term service.

[0042] In the fourth aspect, the embodiments of the present invention provide a titanium alloy brake disc for high-speed trains, which includes a brake disc substrate and a laser cladding layer on the surface of the brake disc. The material of the brake disc substrate is titanium alloy, and the laser cladding layer is prepared by using the above preparation method.

[0043] The present invention will be further described below with reference to embodiments.

[0044] The performance test methods for the laser cladding layers on the surfaces of the titanium alloy brake discs for high-speed trains in the following examples and comparative examples are as follows:

[0045] Microhardness: The hardness of the coating was tested using a Vickers microhardness tester with a load of 9.8 N and a holding time of 15 s. Each area was tested 5 times, and the average value was taken.

[0046] Friction and wear: The wear resistance of the coating was tested using a friction and wear testing machine. The friction pair was a pin made of copper-based powder metallurgy material. The test load was 60 N, the rotation speed was 300 r / min, and the time was 30 min. The friction coefficient was recorded, and the morphology of the wear scar was measured using a confocal microscope.

[0047] Thermal fatigue performance: Experiments were carried out using an immersion-type thermal fatigue testing machine. The specimen was kept in a furnace at 700 °C for 250 s, and then immersed in cold water for 20 s, which was defined as one thermal fatigue cycle. After every 100 - 200 cycles, the specimen was taken out to observe the surface morphology, and a total of 1000 cycle experiments were carried out.

[0048] Example 1

[0049] The embodiments of the present invention provide a preparation method for a TiNbZr coating of a titanium alloy brake disc for high-speed trains, including the following steps:

[0050] TiNbZrMo provided in this example 0.1The composite alloy powder is prepared through the following steps: Component A and Component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.1. The high-energy ball milling mixing method and parameters are as follows: In the ball milling tank, agate balls with a diameter of 2 - 5 mm are added to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotating clockwise and counterclockwise for 30 min in sequence, standing still for 10 min, and repeating 5 cycles.

[0051] The technological steps for preparing the laser cladding brake disc are as follows:

[0052] 1) Load the TiNbZrMo 0.1 composite alloy powder into the powder feeder of the laser cladding device for standby.

[0053] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra 3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on the resistance preheating plate for 1 h at a preheating temperature of 300 °C.

[0054] 3) Use argon as the shielding gas for laser cladding. The technological parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0055] 4) Keep the brake disc obtained after cladding at 300 °C for heat treatment for 4 h.

[0056] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0057] 6) Perform cold pressing on the coated brake disc obtained after cladding, controlling the deformation amount to be less than ±0.2 mm.

[0058] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra 0.8.

[0059] Example 2

[0060] The TiNbZrMo 0.2 composite alloy powder provided in this example is prepared through the following steps: Component A and Component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.2. The high-energy ball milling mixing method and parameters are as follows: In the ball milling tank, agate balls with a diameter of 2 - 5 mm are added to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotating clockwise and counterclockwise for 30 min in sequence, standing still for 10 min, and repeating 5 cycles.

[0061] The technological steps for preparing the laser cladding brake disc are as follows:

[0062] 1) Load the TiNbZrMo0.2 The composite alloy powder is loaded into the powder feeder of the laser cladding device and reserved.

[0063] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h at a preheating temperature of 300°C.

[0064] 3) Use argon as the shielding gas for laser cladding. The process parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0065] 4) Keep the brake disc obtained after cladding at 300°C for heat treatment for 4 h.

[0066] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0067] 6) Perform cold pressing on the coated brake disc obtained after cladding, and control the deformation amount to be less than ±0.2 mm.

[0068] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra0.8.

[0069] Example 3

[0070] The TiNbZrMo 0.3 composite alloy powder is prepared through the following steps: Component A and component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.3. The high-energy ball milling method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate clockwise and counterclockwise for 30 min in turn, let it stand for 10 min, and repeat 5 cycles.

[0071] The technological steps for preparing the laser cladding brake disc are as follows:

[0072] 1) Load the TiNbZrMo 0.3 composite alloy powder into the powder feeder of the laser cladding device and reserve.

[0073] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h at a preheating temperature of 300°C.

[0074] 3) Use argon as the shielding gas for laser cladding. The process parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0075] 4) Keep the brake disc obtained after cladding at 300 °C for 4 h for heat preservation treatment.

[0076] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0077] 6) Perform cold pressing on the coated brake disc obtained after cladding, and control the deformation amount to be less than ±0.2 mm.

[0078] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra0.8.

[0079] Example 4

[0080] The TiNbZrMo 0.4 composite alloy powder provided in this example is prepared through the following steps: Component A and Component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.4. The high-energy ball milling mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate clockwise and counterclockwise for 30 min in turn, let it stand for 10 min, and repeat 5 cycles.

[0081] The technological steps for preparing the laser cladding brake disc are as follows:

[0082] 1) Load the TiNbZrMo 0.4 composite alloy powder into the powder feeder of the laser cladding device for standby.

[0083] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h, and the preheating temperature is 300 °C.

[0084] 3) Use argon as the shielding gas for laser cladding. The process parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0085] 4) Keep the brake disc obtained after cladding at 300 °C for 4 h for heat preservation treatment.

[0086] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0087] 6) Cold press the coated brake disc obtained after cladding is completed, and control the deformation amount to be less than ±0.2 mm.

[0088] 7) Perform surface machining on the coated brake disc obtained after cladding is completed to ensure that the flatness after turning is Ra0.8.

[0089] Example 5

[0090] The TiNbZrMo 0.5 composite alloy powder is prepared through the following steps: Component A and component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.5. The high-energy ball milling mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate clockwise and counterclockwise for 30 min in sequence, stand still for 10 min, and repeat 5 cycles.

[0091] The technological steps for preparing the laser cladding brake disc are as follows:

[0092] 1) Load the TiNbZrMo 0.5 composite alloy powder into the powder feeder of the laser cladding device for standby.

[0093] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h, and the preheating temperature is 300 °C.

[0094] 3) Use argon as the shielding gas for laser cladding. The technological parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0095] 4) Keep the brake disc obtained after cladding is completed at 300 °C for 4 h for heat preservation treatment.

[0096] 5) Take out the coated brake disc obtained after cladding is completed from the tooling to release stress.

[0097] 6) Cold press the coated brake disc obtained after cladding is completed, and control the deformation amount to be less than ±0.2 mm.

[0098] 7) Perform surface machining on the coated brake disc obtained after cladding is completed to ensure that the flatness after turning is Ra0.8.

[0099] Comparative Example 1

[0100] This comparative example is the TC4 brake disc substrate without laser cladding coating, and its chemical composition is shown in the following table. It should be noted that the chemical composition of the TC4 brake disc substrate in the above embodiments is the same as that of this comparative example.

[0101] Component Al V Fe C N H Ti Content (wt%) 5.5～6.75 3.5～4.5 ≤0.3 ≤0.1 ≤0.05 ≤0.015 Balance

[0102] Comparative Example 2

[0103] The TiNbZr alloy powder provided in this comparative example includes, by mass percentage: Ti elemental powder: 20.63%, Nb elemental powder: 40.05%, Zr elemental powder: 39.32%, and is mixed by high-energy ball milling according to the above ratio. The high-energy ball milling mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate clockwise and counterclockwise for 30 min in turn, stand still for 10 min, and repeat 5 cycles.

[0104] The technological steps for preparing the laser cladding brake disc are as follows:

[0105] 1) Load the TiNbZr alloy powder into the powder feeder of the laser cladding device and set aside.

[0106] 2) Grind the surface of the TC4 brake disc substrate until it is flat, with a surface roughness of Ra 3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h, and the preheating temperature is 300 °C.

[0107] 3) Use argon as the shielding gas for laser cladding. The technological parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0108] 4) Keep the brake disc obtained after cladding at 300 °C for 4 h for heat treatment.

[0109] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0110] 6) Perform cold pressing on the coated brake disc obtained after cladding, and control the deformation amount to be less than ±0.2 mm.

[0111] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra 0.8.

[0112] Comparative Example 3

[0113] The TiNbZrMo provided in this example 0.6The composite alloy powder is prepared by the following steps: Component A and Component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.6. The high-energy ball milling mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate in the clockwise and counterclockwise directions for 30 min in turn, stand still for 10 min, and repeat 5 cycles.

[0114] The technological steps for preparing the laser cladding brake disc are as follows:

[0115] 1) Put the TiNbZrMo 0.6 composite alloy powder into the powder feeder of the laser cladding device for standby.

[0116] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra 3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h, and the preheating temperature is 300 °C.

[0117] 3) Use argon as the shielding gas for laser cladding. The process parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0118] 4) Keep the brake disc obtained after cladding at 300 °C for heat treatment for 4 h.

[0119] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0120] 6) Perform cold pressing on the coated brake disc obtained after cladding, and control the deformation amount to be less than ±0.2 mm.

[0121] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra 0.8.

[0122] Comparative Example 4

[0123] The TiNbZrNi alloy powder provided in this comparative example, by mass percentage, includes: Ti elemental powder: 16.46%, Nb elemental powder: 31.96%, Zr elemental powder: 31.38%, Ni elemental powder: 20.20%. Mix them by high-energy ball milling according to the above ratio. The high-energy ball milling mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm into the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate in the clockwise and counterclockwise directions for 30 min in turn, stand still for 10 min, and repeat 5 cycles.

[0124] The technological steps for preparing the laser cladding brake disc are as follows:

[0125] 1) Load the TiNbZr alloy powder into the powder feeder of the laser cladding device for standby.

[0126] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra 3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h at a preheating temperature of 300 °C.

[0127] 3) Use argon as the shielding gas for laser cladding. The process parameters are as follows: laser power 3000 W, scanning speed 3.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0128] 4) Keep the brake disc obtained after cladding at 300 °C for heat treatment for 4 h.

[0129] 5) Take out the coated brake disc obtained after cladding from the tooling to release stress.

[0130] 6) Perform cold pressing on the coated brake disc obtained after cladding, controlling the deformation amount to be less than ±0.2 mm.

[0131] 7) Perform surface machining on the coated brake disc obtained after cladding to ensure that the flatness after turning is Ra 0.8.

[0132] Comparative Example 5

[0133] The TiNbZrMo 0.4 alloy powder provided in this comparative example, by mass percentage, includes: Ti elemental powder: 22.24%, Nb elemental powder: 27.84%, Zr elemental powder: 35.68%, Mo elemental powder: 14.24%, and perform high-energy ball milling and mixing according to the above ratio. The high-energy ball milling and mixing method and parameters are as follows: Add agate balls with a diameter of 2 - 5 mm to the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, rotate clockwise and counterclockwise for 30 min in turn, let it stand for 10 min, and repeat 5 cycles.

[0134] The process steps for preparing the laser cladding brake disc are as follows:

[0135] 1) Load the TiNbZr composite alloy powder into the powder feeder of the laser cladding device for standby.

[0136] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra 3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on a resistance preheating plate for 1 h at a preheating temperature of 300 °C.

[0137] 3) Argon is used as the shielding gas for laser cladding, and the process parameters are as follows: laser power 3400 W, scanning speed 2.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0138] 4) The brake disc obtained after cladding is heat-treated at 300 °C for 4 h.

[0139] 5) The coated brake disc obtained after cladding is taken out of the tooling to release stress.

[0140] 6) The coated brake disc obtained after cladding is cold-pressed, and the deformation amount is controlled to be less than ±0.2 mm.

[0141] 7) The coated brake disc obtained after cladding is surface machined to ensure that the flatness after turning is Ra0.8.

[0142] Comparative Example 6

[0143] The TiNbZrMo 0.4 composite alloy powder provided in this example is prepared by the following steps: Component A and Component B are mixed by high-energy ball milling according to an atomic ratio of 3:0.4. The high-energy ball milling mixing method and parameters are as follows: Agate balls with a diameter of 2 - 5 mm are added to the ball milling tank to promote uniform mixing of the powder. The revolution speed is 180 r / min, and it rotates clockwise and counterclockwise for 30 min in turn, stands still for 10 min, and repeats 5 cycles.

[0144] The process steps for preparing the laser-clad brake disc are as follows:

[0145] 1) Load the TiNbZrMo 0.4 composite alloy powder into the powder feeder of the laser cladding device for standby.

[0146] 2) Grind the surface of the TC4 brake disc substrate to be flat, with a surface roughness of Ra3.2 - 6.3. Clean the surface of the brake disc with anhydrous ethanol and acetone to remove impurities. Preheat the brake disc substrate on the resistance preheating plate for 1 h, and the preheating temperature is 300 °C.

[0147] 3) Argon is used as the shielding gas for laser cladding, and the process parameters are as follows: laser power 3400 W, scanning speed 2.5 mm / s, powder feeding speed 0.8 r / min, overlapping rate 50%, and shielding gas flow rate 25 L / min.

[0148] 4) The brake disc obtained after cladding is heat-treated at 300 °C for 4 h.

[0149] 5) The coated brake disc obtained after cladding is taken out of the tooling to release stress.

[0150] 6) After the cladding is completed, the coated brake disc is subjected to cold pressing, and the deformation amount is controlled to be less than ±0.2 mm.

[0151] 7) The coated brake disc obtained after the cladding is completed is subjected to surface machining to ensure that the flatness after turning is Ra0.8.

[0152] Table 1 below shows the composition of the coatings on the surface of the titanium alloy substrate in the examples and comparative examples.

[0153] Table 1

[0154]

[0155]

[0156] Table 2 below shows the test results of the coatings on the surface of the titanium alloy substrate in the examples and comparative examples:

[0157] Table 2

[0158]

[0159]

[0160] Figure 1 are the results of penetrant inspection and surface forming of the laser cladding coatings obtained in Examples 1 to 5, Comparative Examples 3 to 4, and Comparative Example 6 of the present invention. Among them Figure 1 (a - e) in are the penetrant inspection diagrams of Examples 1 to 5, (f - g) are the penetrant inspection diagrams of Comparative Examples 3 to 4, and (h) is the surface forming situation of Comparative Example 6. It can be seen from Figure 1 that: the forming of the high - entropy alloy coatings (a - e) on the surface of the substrate in Examples 1 to 5 is good and no cracks appear; cracks appear in the high - entropy alloy coatings of Comparative Example 3 and Comparative Example 4, indicating that increasing the Mo element or changing the element type will affect the forming quality; the laser energy of Comparative Example 6 (h) is too large, the coating surface is oxidized and yellowed, and the substrate is deformed.

[0161] Figure 2 is the micro - structure diagram of the coating in Example 2 of the present invention. Among them Figure 2 (a) in is the metallographic diagram of the interface between the coating and the substrate, and (b) is the metallographic structure diagram of the top of the coating. The coating and the substrate achieve metallurgical bonding. Coarse dendritic crystals are formed in 1 - 3 layers close to the substrate, and the 4th layer is composed of dendritic crystals and cellular crystals together.

[0162] Figure 3 is the diagram of the change in micro - hardness in the vertical direction of the coatings in Examples 1 to 5 of the present invention. It can be seen that: as the content of the Mo element increases, the hardness of the coating increases.

[0163] Figure 4 It is the friction coefficient curve of the friction and wear experiments on the coatings of Embodiments 1 to 5, Comparative Examples 1 to 2, and Comparative Example 5 of the present invention. It can be seen that: the friction coefficients of Embodiments 1 to 5 first decrease and then increase. Among them, the friction coefficients of Embodiments 2 and 4 are stable within the range of 0.28 to 0.44, meeting the friction coefficient requirements of the brake disc. The friction coefficients of Comparative Examples 1 and 2 have a tendency to increase with time and are not stable. The friction coefficient of Comparative Example 5 is unstable and not within the range of 0.28 to 0.44.

[0164] Figure 5 It is the wear profile diagram after the friction and wear experiments on the coatings of Embodiments 4 to 5, Comparative Examples 1 to 2 of the present invention. It can be seen that: the wear mark widths and depths of Comparative Examples 1 and 2 are larger than those of Embodiments 4 and 5, indicating that the wear amount of the comparative examples is larger and the wear resistance is inferior to that of the embodiments.

[0165] Figure 6 It is the surface morphology of Embodiments 1 to 2 and Comparative Example 1 of the present invention after 1000 thermal fatigue tests. It can be seen that: in Comparative Example 1, pits are formed on the surface due to oxidation in a high-temperature environment and the whole is bent. The surfaces of Embodiments 4 and 5 are also oxidized, but the degree of oxidation is weakened compared with that of Comparative Example 1 and the whole does not deform.

[0166] Combined with the above table and Figures 1 - 6 , it can be seen that in the embodiments of the present invention, the enhanced coating of the high-entropy alloy formed by laser cladding of the above TiNbZrMo composite powder on the surface of the titanium alloy matrix can improve the wear resistance of the brake disc surface, meet the service requirements of more demanding working conditions, and further extend the service life of the brake disc, having good economic benefits.

[0167] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-entropy alloy coating, characterized in that, The chemical composition of the high-entropy alloy coating is TiNbZrMo, and its microstructure is a body-centered cubic solid solution composed of dendrites and cellular crystals.

2. The high-entropy alloy coating according to claim 1, characterized in that, In the high-entropy alloy coating, the atomic ratio of Ti, Nb, Zr and Mo elements is 3:(0.1-0.5). Among the three elements of Ti, Nb and Zr, the mass fraction of Ti element is 11.51-20.63%, the mass fraction of Nb element is 40.05-44.65%, and the mass fraction of Zr element is 39.32-43.84%.

3. The high-entropy alloy coating according to claim 1, characterized in that, The high-entropy alloy coating is a multi-layer structure, with each layer having a thickness of 0.8-1 mm and a total thickness of 3.5-5 mm.

4. The high-entropy alloy coating according to claim 1, wherein The friction coefficient of the high-entropy alloy coating is in the range of 0.28-0.44, and the microhardness reaches above 360 Hv.

5. A method for preparing a high-entropy alloy coating according to any one of claims 1 to 4, characterized in that, It includes: The high-entropy alloy coating is formed on the surface of the substrate by laser cladding.

6. The preparation method according to claim 5, characterized in that, It includes the following steps: The composite powder of Ti powder, Nb powder, Zr powder and Mo powder is dried in a vacuum drying oven at 80 °C for 2 h and then loaded into a powder feeder, and laser cladding is used to prepare the coating. Among them, the process parameters of laser cladding are: the cladding speed is 3-3.5 mm / s, the laser spot diameter is 4 mm, the laser power is 2800-3200 W, the coaxial powder feeding method, the powder feeding speed is 0.8-1.0 r / min, and the protective gas flow rate is 25 L / min; Preferably, the laser cladding layer is formed by multi-pass laser cladding, and the overlapping rate between adjacent pass cladding layers is 40%-50%, and the laser cladding parameters of each pass are the same.

7. The preparation method according to claim 5, characterized in that, The preparation method of the mixed powder is as follows: Ti powder, Nb powder, Zr powder and Mo powder are mixed by high-energy ball milling according to the ratio. Among them, the ball milling speed is 150-180 r / min, and it rotates clockwise and counterclockwise for 30-45 min in turn, stands for 10 min, and repeats 5 cycles; Preferably, Ti powder, Nb powder, Zr powder and Mo powder are all high-purity spherical powders with a purity of 99.99%, and the powder diameter is 53-150 μm.

8. The preparation method according to claim 5, wherein It also includes: Before laser cladding, the surface of the substrate is polished and cleaned, then preheated to 300 °C, argon is used as the protective gas for laser cladding, and the temperature of the brake disc is maintained at 280 °C-320 °C during the cladding process. After the cladding is completed, heat preservation treatment is carried out at a temperature of 300 °C-400 °C for 3-4 h; Preferably, after the heat preservation treatment is completed, the substrate with the coating is taken out, and then cold pressing treatment is carried out, and the deformation amount is controlled to be less than ±0.2 mm; Preferably, the substrate is a titanium alloy, more preferably a titanium alloy brake disc, and further preferably a high-speed train titanium alloy brake disc.

9. An application of a high-entropy alloy coating prepared according to the high-entropy alloy coating described in any one of claims 1 to 4 or the preparation method described in any one of claims 5 to 8, characterized in that, The high-entropy alloy coating is applied to the surface of the titanium alloy brake disc.

10. A titanium alloy brake disc for high-speed trains, characterized in that, It includes a brake disc substrate and a laser cladding layer on the surface of the brake disc. The material of the brake disc substrate is a titanium alloy, and the laser cladding layer is prepared by using the preparation method described in any one of claims 5-8.

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