Double-gradient high-temperature-resistant high-entropy alloy wear-resistant layer and ultrasonic-assisted laser cladding preparation method thereof

Abstract

The invention discloses a double-gradient high-temperature-resistant high-entropy alloy wear-resistant layer and an ultrasonic-assisted laser cladding preparation method thereof, and belongs to the technical field of metal material coatings and surface modification. A proper amount of refractory element W with anti-oxidation and solid solution strengthening effects is introduced into a CoCrFeNi high-entropy alloy coating, an ultrasonic-assisted laser cladding process is adopted, the wear-resistant layer with the grain size and the precipitated phase volume fraction in a gradient structure from exterior to interior is prepared, local stress concentration caused by W aggregation in the laser cladding process is improved, and the wear-resistant performance of the CoCrFeNi high-entropy alloy coating is improved. And the metallurgical bonding strength of the cladding layer and the matrix is improved, and the high-temperature friction and wear resistance of the cladding layer is enhanced. The cladding layer is fine and compact in structure, in gradient distribution, good in mechanical property and excellent in high-temperature wear resistance. The method is easy to operate and low in cost, and an effective method is provided for improving highly coordinated regulation of process-structure-performance and preparing the novel high-temperature-resistant high-entropy alloy wear-resistant layer.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material coating and surface modification, and in particular to a double-gradient high-temperature resistant high-entropy alloy wear-resistant layer and an ultrasonic-assisted laser cladding preparation method thereof. Background Art

[0002] High-entropy alloys (HEAs) are a multi-principal alloy system, usually composed of five or more metals. As a new type of metal material with unique characteristics, it has attracted the attention of many researchers. Due to the high mixing entropy, the Gibbs free energy is reduced, and HEAs usually have a simple phase composition. Through appropriate composition design, alloy materials with ideal properties such as high strength and good ductility, good high temperature resistance and oxidation resistance, high fracture toughness, fatigue resistance, and wear resistance can be obtained. However, due to the high production cost of high entropy alloys, their development and application as structural materials are limited. By preparing a high entropy alloy protective layer, not only can the excellent properties of high entropy alloys be maintained, but also the production cost can be greatly saved.

[0003] CoCrFeNi high entropy alloy is a multi-principal FCC structure high entropy alloy. Its low stacking fault energy is conducive to the formation of deformation twins, thus having strong plastic toughness. However, the low strength of CoCrFeNi high entropy alloy limits its application in mechanical equipment. According to the cocktail effect, the properties of high entropy alloys can be effectively adjusted by introducing different contents of specific elements into high entropy alloys. For the W element, it has a large atomic size and forms a solid solution with other elements, resulting in obvious lattice distortion, thereby significantly improving the dislocation anti-slip ability of the alloy. At the same time, the unmelted W particles form a hard phase with the generated μ phase, further strengthening the mechanical properties of the alloy, especially in terms of wear resistance. However, as a refractory metal element, W is often easy to aggregate during the forming process, causing local stress concentration, resulting in deterioration of the mechanical properties of the alloy.

[0004] Chinese patent CN202211022745.9 discloses a high-entropy alloy-based high-temperature solid lubricating coating and a preparation method thereof. The raw material composition of the coating is 100%, and the components and their mass percentages are: CoCrFeNiW 0.2～0.5 High entropy alloy powder 70% to 90%, Ag powder 10% to 30%; the coating is prepared by cold air power spraying technology and has good tribological properties and load-bearing properties. 0.2～0.5 High entropy alloy is the bonding phase, W is a metal element with a high melting point, and as an alloying element it can improve the CoCrFeNiW 0.2～0.5The melting point, strength and hardness of the high entropy alloy, and its oxidation product WO3 at high temperature has a low friction coefficient, which is beneficial to the comprehensive improvement of the high-temperature mechanical properties and tribological properties of the coating; the coating is mainly lubricated by Ag at medium and low temperatures, and the multi-component composite oxides generated by the oxidation of Ag and alloy elements at high temperatures jointly play a lubricating role, which can ensure that the coating has a low friction coefficient and wear rate in the range of room temperature to 1000°C.

[0005] Laser cladding is an important method for material surface modification. It uses high-energy-density lasers to quickly melt alloys of different compositions and properties with the substrate surface, forming an alloy layer on the substrate surface that has completely different compositions and properties from the substrate. Laser cladding is widely used in surface strengthening and repair of various components due to its fast cooling speed, small heat-affected zone, good bonding with the substrate, and wide range of applications. However, due to the extremely fast heating and cooling speeds during laser cladding, the liquid metal is not replenished in time during the solidification process, and a large number of vacancies, dislocations and other defects are generated during the solid-state cooling and shrinkage process. At the same time, cracks are easily generated under the tensile stress of the surrounding colder substrate. Therefore, in order to make full use of the excellent properties of high-entropy alloys and solve the problem of coating cracking, ultrasonic-assisted laser cladding has become an effective means to uniform the organization and reduce the residual stress of the coating, thereby inhibiting cracks. The study found that the acoustic streaming effect generated by ultrasound accelerated the original Marangoni flow and solute diffusion in the molten pool, promoted the discharge of gas, and at the same time, due to the influence of ultrasonic thermal effect, the life cycle of the molten pool was extended and the temperature of the molten pool increased, providing time conditions for the solute exchange between the powder melt and the matrix melt, ensuring the uniformity of the organizational composition in the molten pool and reducing the local stress concentration caused by element aggregation. The increase in the molten pool temperature lengthened the cooling time of the molten pool, greatly reducing the residual stress during the rapid cooling process and reducing the nucleation of cracks.

[0006] For external non-contact input ultrasonic conduction, the ultrasonic wave acts on the cladding layer through the air as the medium, and part of the ultrasonic vibration energy will act on the liquid metal atoms to generate vibration, which leads to the maximum effect of the ultrasonic wave on the solidification of the top metal. Therefore, due to the different vibration auxiliary effects of the ultrasonic wave on different parts of the cladding layer, the refinement and uniformity of the surface grains and precipitated phases are most obvious, thus providing conditions for the preparation of the gradient wear-resistant layer. The formation of the gradient coating can accommodate more plastic deformation, thereby effectively suppressing the strain localization caused by sliding, suppressing crack propagation and stratification of the surface material, thereby improving the fracture toughness and wear resistance of the coating.

[0007] Therefore, the present invention aims to propose a method for preparing a double-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding, which synergistically improves its overall high-temperature wear resistance by regulating the high-entropy alloy composition, laser cladding parameters and ultrasonic parameters. Summary of the invention

[0008] In order to improve the shortcomings of the high-temperature wear resistance of CoCrFeNi high-entropy alloy, the purpose of the present invention is to provide a dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer and an ultrasonic-assisted laser cladding preparation method thereof, by introducing the refractory element W with antioxidant and solid solution strengthening effects into the CoCrFeNi alloy to enhance its high-temperature wear resistance, and at the same time, in order to eliminate defects such as pores and cracks generated during the laser cladding process, uniform the structure and composition of the coating, ultrasonic-assisted laser cladding is used, and the process parameters are controlled, so that the wear-resistant layer finally obtained is tightly combined with the substrate, has a dense structure, and has a uniform composition. The coating microstructure refinement effect is obvious and is distributed in a gradient; the dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer has strong high-temperature stability and good high-temperature wear resistance.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a double-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding, wherein the double-gradient high-temperature resistant high-entropy alloy wear-resistant layer is prepared on the surface of a substrate by ultrasonic-assisted laser cladding technology, and specifically comprises the following steps:

[0011] (1) preparing a cladding material: mixing CoCrFeNi high entropy alloy powder and elemental W powder in a molar ratio of 4:(0.6-1) to obtain the cladding material;

[0012] (2) Surface pretreatment of the steel substrate;

[0013] (3) Preparation of a dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer: laser cladding is performed under a protective atmosphere and ultrasonic wave to form the dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer on the surface of the substrate; the laser cladding parameters are: a powder feeding rate of 10 to 20 g / min, a laser power of 1500 to 3000 W, a scanning speed of 2 to 5 mm / s, and an overlap rate of 20 to 40%.

[0014] In the above step (1), the particle size of the cladding material is 45 to 105 μm, and the molar ratio of Co, Cr, Fe and Ni in the CoCrFeNi high entropy alloy powder is 1:1:1:1; the CoCrFeNi high entropy alloy powder is a spherical powder with a purity of more than 99.9% prepared by vacuum gas atomization.

[0015] In the above step (1), the mixing process is carried out using a three-dimensional mixer with the following parameters: mixing time 1-3h, rotation speed 60-70r / min, running for 550-650s and stopping for 300s; the mixed powder is dried at 70-95°C for 6-10h.

[0016] In the above step (2), the pretreatment process of the steel substrate is as follows: before the coating is prepared, it is finely ground with 120-400 mesh sandpaper to ensure smoothness, and then the ground substrate is ultrasonically cleaned in anhydrous ethanol for 10-20 minutes to remove surface oil and impurities.

[0017] In the above step (3), when ultrasonic waves are used, the ultrasonic frequency is 15-25KHZ, propagating through the air medium to act on the cladding layer, with a defocus of 55-60mm, a depression angle of 25-35°, and an amplitude of 40-65%.

[0018] A double-gradient high-temperature resistant high-entropy alloy wear-resistant layer was prepared by the above method. The wear-resistant layer was a CoCrFeNiW high-entropy alloy. The molar ratio of Co, Cr, Fe, Ni and W in the alloy was 1:1:1:1:(0.6-1).

[0019] Furthermore, the grain size and the volume fraction of the precipitated phase of the wear-resistant layer both show gradient variation characteristics from the outside to the inside, specifically: the grain size of the wear-resistant layer gradually increases from the outside to the inside, and the volume fraction of the precipitated phase of the wear-resistant layer gradually decreases from the outside to the inside.

[0020] Furthermore, in the wear-resistant layer, the thickness of the fine-grained zone near the surface is 400μm to 600μm, the grain size of the fine-grained zone is 37μm to 126μm, the volume fraction of the precipitation phase in the fine-grained zone is 30% to 40%, and the precipitation phase in the fine-grained zone is dispersedly distributed in granular form; the thickness of the internal coarse-grained zone is 800μm to 1200μm, the grain size of the coarse-grained zone is 93μm to 312μm, the volume fraction of the precipitation phase in the coarse-grained zone is 20% to 30%, and the precipitation phase in the coarse-grained zone is concentratedly distributed in a network form.

[0021] The design mechanism of the present invention is as follows:

[0022] The present invention is used in laser cladding CoCrFeNiW 0.6-1 During the process, ultrasonic waves are applied to the molten pool, and the cavitation effect, thermal effect and acoustic flow effect of ultrasonic waves are used to uniformly organize the composition and eliminate defects such as pores and cracks in laser cladding. At the same time, by adjusting the amplitude of ultrasonic waves, a dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer of grain size and precipitation phase is prepared. The grain refinement effect of the wear-resistant layer near the surface is obvious, mostly equiaxed grains, and the precipitation phase is dispersed in a granular form. The internal grains are relatively coarse, mostly columnar crystals, and the precipitation phase is concentrated in a network, with a gradient distribution from the surface to the inside. The fine grains and dispersed precipitation phases in the near-surface area provide the wear-resistant layer with a higher hardness and play a role in wear resistance. The internal coarse crystals serve as a low-hardness area. Due to their strong plasticity, they release the stress transmitted from the near-surface area. The network precipitation phase allows part of the stress to be directly transmitted to the matrix, enhancing the stability of the wear-resistant layer. Since the precipitation phase is a W-rich metal compound with extremely strong high-temperature stability, the overall high-temperature wear resistance is further improved.

[0023] Beneficial effects of the present invention:

[0024] (1) The present invention introduces the high melting point and oxidation resistant W element into the CoCrFeNi alloy to enhance its high temperature wear resistance.

[0025] (2) The present invention uses ultrasonic wave to assist laser cladding, which makes the structure and composition of the coating uniform and eliminates defects such as pores and cracks generated during the laser cladding process.

[0026] (3) The present invention prepares a high-temperature high-entropy alloy wear-resistant layer with a double gradient of grain size and precipitation phase by regulating the amplitude of ultrasonic waves, thereby improving the high-temperature wear resistance of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Example 1: Ultrasonic 50% amplitude assisted laser cladding of CoCrFeNiW 0.8 Cross-sectional optical microstructure image of the wear-resistant layer of the double-gradient high-temperature high-entropy alloy;

[0028] Figure 2 Example 1: Ultrasonic 50% amplitude assisted laser cladding of CoCrFeNiW 0.8 Cross-sectional SEM image of the wear-resistant layer of the dual-gradient high-temperature high-entropy alloy.

[0029] Figure 3 Example 1: Ultrasonic 50% amplitude assisted laser cladding of CoCrFeNiW 0.8 Cross-sectional EBSD image of the wear-resistant layer of a double-gradient high-temperature high-entropy alloy;

[0030] Figure 4 CoCrFeNiW prepared by laser cladding in Example 1 and Comparative Examples 1-2 0.8 High temperature friction coefficient of high-entropy alloy wear-resistant layer;

[0031] Figure 5 CoCrFeNiW prepared by laser cladding in Example 1 and Comparative Examples 1-2 0.8 Wear rate of high temperature high entropy alloy wear-resistant layer;

[0032] Figure 6 CoCrFeNiW prepared by laser cladding in Example 1 and Comparative Examples 1-2 0.8 Wear curve of high temperature resistant high entropy alloy wear-resistant layer.

[0033] Figure 7 This is a working principle diagram of the present invention using ultrasonic-assisted laser cladding to prepare a wear-resistant layer. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0035] The laser cladding experimental equipment in the following embodiments includes a fiber laser (RFL-C3000), a Bronte 6-DOF industrial robot and a powder feeding system. The laser cladding powder feeding speed is 10-20 g / min, the laser power is 1500-3000 W, the scanning speed is 2-5 mm / s, and the overlap rate is 20-40%. The ultrasonic equipment includes a digital intelligent ultrasonic generator with a frequency of 20 KHZ, which acts on the cladding layer through air medium. The ultrasonic working parameters are: defocus 57 mm, depression angle 30 °, amplitude 40-65%.

[0036] The working principle of ultrasonic-assisted laser cladding to prepare wear-resistant layer is as follows Figure 7 As shown, the laser and the ultrasonic generator are both located above the substrate, the light beam emitted by the laser is projected perpendicularly to the upper surface of the substrate, and the angle (depression angle) between the incident direction of the ultrasonic wave and the upper surface of the substrate is 30°.

[0037] Embodiment 1:

[0038] This example prepares a dual-gradient high-temperature resistant CoCrFeNiW 0.8 The process of high entropy alloy wear-resistant layer is as follows:

[0039] 1. Preparation of cladding material: It is a mixture of CoCrFeNi spherical prefabricated alloy powder (prepared by vacuum gas atomization method) with a purity of more than 99.9% and single substance W powder. The molar ratio of Co, Cr, Fe and Ni in the CoCrFeNi alloy powder is 1:1:1:1; the molar ratio of CoCrFeNi alloy powder to W powder is 4:0.8; the particle size of the cladding material powder is 45μm~105 microns; the mixing process of the two powders is carried out using a three-dimensional mixer, the mixing time is 2h, the mixer speed is 65r / min, and it stops for 300s every 600s; the mixed cold powder is dried at 80℃ for 8h to ensure the fluidity of the material.

[0040] 2. Surface pretreatment of steel substrate: Select 45# steel with dimensions of 150 mm in length, 100 mm in width and 15 mm in thickness as the substrate. Before preparing the wear-resistant layer, finely grind it with 120-400 mesh sandpaper to ensure a smooth surface. Then ultrasonically clean the polished substrate in anhydrous ethanol for 15 minutes to remove surface oil and impurities.

[0041] 3. Use ultrasonic-assisted laser cladding to prepare a double-gradient high-temperature-resistant high-entropy alloy wear-resistant layer:

[0042] Performing laser cladding under a protective atmosphere and ultrasonic waves to form the dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer on the surface of the substrate;

[0043] Among them: the process parameters of laser cladding are: powder feeding rate 15g / min, laser power 2000W, scanning speed 3mm / s, single layer multi-pass cladding, overlap rate 30%, high purity argon gas is used as protective gas, and high entropy alloy is clad on the surface of 45# steel. The frequency of the ultrasonic equipment is 20KHZ, which acts on the cladding layer through air medium. The working parameters of the ultrasonic equipment are: defocus 57mm, depression angle 30°, and adjustment amplitude of 50%.

[0044] 4. Characterization test of microstructure and performance of high entropy alloy wear-resistant layer:

[0045] (1) Optical microscope observation:

[0046] The microstructure of the prepared wear-resistant layer was observed using an optical microscope. Figure 1 This is the CoCrFeNiW prepared by ultrasonic 50% amplitude laser cladding in this embodiment. 0.8 The cross-sectional optical microstructure image of the dual-gradient high-temperature high-entropy alloy wear-resistant layer shows that the cladding layer is tightly bonded to the substrate, the coating structure is dense, and there are no obvious cracks and holes.

[0047] (2) Scanning electron microscopy observation:

[0048] The microstructure of the prepared wear-resistant layer was observed using a scanning electron microscope. Figure 2 This is the CoCrFeNiW prepared by ultrasonic 50% amplitude laser cladding in this embodiment. 0.8 The cross-sectional SEM image of the double-gradient high-temperature high-entropy alloy wear-resistant layer after aqua regia corrosion shows that the wear-resistant layer prepared by ultrasonic-assisted laser cladding has a fine and uniform structure, and most of the grains are equiaxed. The μ phase precipitated in the upper part of the wear-resistant layer (near the surface) is dispersed in a granular shape due to the ultrasonic effect, and the μ phase precipitated in the lower part (inside) is concentrated in a network shape due to the weakening of the ultrasonic effect. The grain structure of the wear-resistant layer sample was analyzed by electron backscatter diffraction (EBSD). Figure 3 In this embodiment, ultrasonic 50% amplitude assisted laser cladding CoCrFeNiW 0.8 The cross-sectional EBSD image of the double-gradient high-temperature high-entropy alloy wear-resistant layer after electrolytic polishing shows that the upper grain refinement effect is obvious, mostly equiaxed grains, and the lower grains are relatively coarse, mostly columnar crystals. The grain size increases gradiently from the surface to the inside.

[0049] (3) Microhardness test:

[0050] The microhardness of the wear-resistant layer was measured using a microhardness tester (FM-700) with a load of 300 g and a duration of 15 s. The hardness test results were 377.9 HV to 455.3 HV, with an average hardness value of 413.5 HV.

[0051] (4) High temperature wear resistance test:

[0052] A reciprocating high temperature friction and wear tester was used to conduct a 900℃ dry wear test on the wear-resistant layer sample. The corresponding test object was a gallium nitride ceramic ball with a diameter of 5 mm. The load, frequency, and wear time were 12N, 2Hz, and 30min, respectively. Figure 4 It can be seen that the high temperature friction coefficient is between 0.6 and 0.7. Figure 5 It can be seen that the wear rate is 166.45μm 3 / (N·m), Figure 6 It can be seen that the widest part of the wear scar is about 8 μm.

[0053] Comparative Example 1:

[0054] In this case, CoCrFeNiW was prepared by laser cladding. 0.8 High entropy alloy wear-resistant layer, the specific process is as follows:

[0055] 1. Preparation of cladding material: It is a mixture of CoCrFeNi spherical prefabricated alloy powder (prepared by vacuum gas atomization) with a purity of more than 99.9% and single substance W powder. The molar ratio of Co, Cr, Fe and Ni in the CoCrFeNi alloy powder is 1:1:1:1, and the molar ratio of CoCrFeNi alloy powder to W powder is 4:0.8; the particle size of the cladding material powder is 45μm~105 microns; the mixing process of the two powders is carried out using a three-dimensional mixer, the mixing time is 2h, the mixer speed is 65r / min, the operation is 600s, and the cooling is 300s; the mixed powder is dried at 80℃ for 8h to ensure the fluidity of the material.

[0056] 2. Surface pretreatment of steel substrate: Select 45# steel with a size of 150mm×100mm×15mm as the substrate. Before preparing the wear-resistant layer, finely grind it with 120-400 mesh sandpaper to ensure a smooth surface. Ultrasonic clean the polished substrate in anhydrous ethanol for 15 minutes to remove surface oil and impurities.

[0057] 3. Preparation of CoCrFeNiW by laser cladding 0.8 High entropy alloy wear-resistant layer:

[0058] Laser cladding is carried out under a protective atmosphere to form a high entropy alloy wear-resistant layer on the surface of the substrate.

[0059] The process parameters of laser cladding are: powder feeding speed 15g / min, laser power 2000W, scanning speed 3mm / s, overlap rate 30%, high-purity argon as protective gas, single-layer multi-pass cladding, and high-entropy alloy coating on the surface of 45# steel.

[0060] 4. Characterization test of high entropy alloy coating structure and performance:

[0061] (1) Microhardness test:

[0062] The microhardness of the coating was measured using a microhardness tester (FM-700) with a load of 300 g and a duration of 15 s. The hardness test results were 242.9 HV to 287.2 HV, with an average hardness value of 264.9 HV.

[0063] (2) High temperature wear resistance test:

[0064] A reciprocating high temperature friction and wear tester was used to conduct a 900℃ dry wear test on the wear-resistant layer sample. The corresponding test object was a gallium nitride ceramic ball with a diameter of 5 mm. The load, frequency, and wear time were 12N, 2Hz, and 30min, respectively. Figure 4 It can be seen that the high temperature friction coefficient is between 1.5 and 1.7, which is much higher than that of Example 1; Figure 5 It can be seen that the wear rate is 2518.61μm 3 / (N·m), much higher than that in Example 1; Figure 6 It can be seen that the widest part of the wear scar is about 36 μm, which is wider than that of Example 1.

[0065] Comparative Example 2:

[0066] In this case, CoCrFeNiW was prepared by ultrasonic-assisted laser cladding. 0.8 High entropy alloy wear-resistant layer, the specific process is as follows:

[0067] 1. Preparation of cladding material: It is a mixture of CoCrFeNi spherical prefabricated alloy powder (prepared by vacuum gas atomization) with a purity of more than 99.9% and single W powder. The molar ratio of Co, Cr, Fe and Ni in the CoCrFeNi alloy powder is 1:1:1:1; the molar ratio of CoCrFeNi alloy powder to W powder is 4:0.8; the particle size of the cladding material powder is 45μm~105 microns; the mixing process of the two powders is carried out using a three-dimensional mixer, the mixing time is 2h, the mixer speed is 65r / min, and it stops for 300s every 600s; the mixed cold powder is dried at 80℃ for 8h to ensure the fluidity of the material.

[0068] 2. Surface pretreatment of steel substrate: Select 45# steel with a size of 150mm×100mm×15mm as the substrate. Before the experiment, finely grind it with 120-400 mesh sandpaper to ensure a smooth surface; ultrasonically clean the polished substrate in anhydrous ethanol for 15 minutes to remove surface oil and impurities.

[0069] 3. Preparation of CoCrFeNiW by ultrasonic-assisted laser cladding 0.8 High entropy alloy wear-resistant layer:

[0070] Laser cladding is performed under the action of a protective atmosphere and ultrasonic waves to form the double-gradient high-temperature resistant high-entropy alloy wear-resistant layer on the surface of the substrate.

[0071] The process parameters of laser cladding are: powder feeding speed 15g / min, laser power 2000W, scanning speed 3mm / s, overlap rate 30%, high-purity argon as protective gas, single-layer multi-pass cladding, and high-entropy alloy cladding on the surface of 45# steel. The frequency of the ultrasonic equipment is 20KHZ, which acts on the cladding layer through air medium. The working parameters of the ultrasonic equipment are: defocus 57mm, depression angle 30°, and adjustment amplitude of 70%.

[0072] 4. Characterization test of high entropy alloy coating structure and performance:

[0073] (1) Microhardness test:

[0074] The microhardness of the coating was measured using a microhardness tester (FM-700) with a load of 300 g and a duration of 15 s. The hardness test results were 234 HV to 262.8 HV, with an average hardness value of 250.5 HV.

[0075] (2) High temperature wear resistance test:

[0076] The sample was subjected to a 900℃ dry wear test using a reciprocating high-temperature friction and wear tester. The corresponding test object was a gallium nitride ceramic ball with a diameter of 5 mm. The load, frequency, and wear time were 12N, 2Hz, and 30min, respectively. Figure 4 It can be seen that the high temperature friction coefficient is between 0.9 and 1. Figure 5 It can be seen that the wear rate is 1181.19μm 3 / (N·m), Figure 6 It can be seen that the widest part of the wear scar is about 29 μm.

[0077] It can be seen from the above results that the preparation method of the double-gradient high-temperature resistant high-entropy alloy wear-resistant layer prepared by ultrasonic-assisted laser cladding provided by the present invention has obvious microstructure refinement effect, presents a double-gradient distribution, can maintain high strength and good plasticity and toughness, and has the advantages of higher surface hardness and better high-temperature wear resistance.

[0078] The embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a double-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding, characterized in that: The method is to prepare a double-gradient high-temperature resistant high-entropy alloy wear-resistant layer on the surface of a substrate using an ultrasonic-assisted laser cladding technology, and specifically includes the following steps: (1) preparing a cladding material: mixing CoCrFeNi high entropy alloy powder and single substance W powder in a molar ratio of 4:(0.6-1) to obtain the cladding material; (2) Surface pretreatment of the steel substrate; (3) Preparation of a dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer: laser cladding is performed under a protective atmosphere and ultrasonic wave to form the dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer on the surface of the substrate; the laser cladding parameters are: a powder feeding rate of 10 to 20 g / min, a laser power of 1500 to 3000 W, a scanning speed of 2 to 5 mm / s, and an overlap rate of 20 to 40%.

2. The method for preparing a dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding according to claim 1, characterized in that: In step (1), the particle size of the cladding material is 45 to 105 μm, and the molar ratio of Co, Cr, Fe and Ni in the CoCrFeNi high entropy alloy powder is 1:1:1:1; the CoCrFeNi high entropy alloy powder is a spherical powder with a purity of more than 99.9% prepared by vacuum gas atomization.

3. The method for preparing a dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding according to claim 1, characterized in that: In step (1), the mixing process is carried out using a three-dimensional mixer with the following parameters: mixing time 1-3h, rotation speed 60-70r / min, running for 550-650s and stopping for 300s; the mixed powder is dried at 70-95°C for 6-10h.

4. The method for preparing a dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding according to claim 1, characterized in that: In step (2), the steel substrate pretreatment process is as follows: before coating preparation, it is finely ground with 120-400 mesh sandpaper to ensure smoothness, and then the ground substrate is ultrasonically cleaned in anhydrous ethanol for 10-20 minutes to remove surface oil and impurities.

5. The method for preparing a dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer by ultrasonic-assisted laser cladding according to claim 1, characterized in that: In step (3), when ultrasonic waves are used, the ultrasonic frequency is 15-25KHZ, propagating through the air medium to act on the cladding layer, with a defocus of 55-60mm, a depression angle of 25-35°, and an amplitude of 40-65%.

6. A dual-gradient high-temperature resistant high-entropy alloy wear-resistant layer prepared by the method described in any one of claims 1 to 5.

7. The method for forming a dual-gradient high-temperature-resistant high-entropy alloy wear-resistant layer according to claim 6, characterized in that: The wear-resistant layer is a CoCrFeNiW high entropy alloy, and the molar ratio of Co, Cr, Fe, Ni and W in the alloy is 1:1:1:1:(0.6-1).

8. The method for forming a dual gradient high temperature resistant high entropy alloy wear-resistant layer according to claim 6, characterized in that: The grain size and the volume fraction of the precipitated phase of the wear-resistant layer both show gradient change characteristics from the surface to the inside, specifically: the grain size of the wear-resistant layer gradually increases from the surface to the inside, and the volume fraction of the precipitated phase of the wear-resistant layer gradually decreases from the surface to the inside.

9. The method for forming a dual gradient high temperature resistant high entropy alloy wear-resistant layer according to claim 7, characterized in that: In the wear-resistant layer, the thickness of the fine-grained zone near the surface is 400μm to 600μm, the grain size of the fine-grained zone is 37μm to 126μm, the volume fraction of the precipitation phase in the fine-grained zone is 30% to 40%, and the precipitation phase in the fine-grained zone is dispersedly distributed in granular form; the thickness of the internal coarse-grained zone is 800μm to 1200μm, the grain size of the coarse-grained zone is 93μm to 312μm, the volume fraction of the precipitation phase in the coarse-grained zone is 20% to 30%, and the precipitation phase in the coarse-grained zone is concentratedly distributed in a network form.

Images