A gradient structure rare earth nitride coated ceramic solid solution strengthened high wear resistance refractory high-entropy alloy coating and a preparation method thereof

Abstract

This invention relates to a gradient-structured rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant refractory high-entropy alloy coating and its preparation method. First, an optimized sol-gel method is used to in-situ coat a nano-scale YN layer onto the surface of micron-sized Si3N4 particles, constructing a core-shell structured YN@Si3N4 composite precursor. Subsequently, this precursor is mixed with pre-alloyed TiZrNbMo high-entropy alloy powder in different proportions, and a base layer, a transition layer, and a wear-resistant functional layer are sequentially constructed on the substrate surface from the inside out using laser cladding technology. The amount of YN@Si3N4 added in this gradient coating increases in a gradient distribution from 0 to 3.0 wt.%, effectively alleviating the thermal stress mismatch between the coating and the substrate. This invention achieves synergistic strengthening through Si substitution solid solution and N interstitial solid solution, while eliminating brittle phase segregation, porosity, and crack defects through gradient structure design and melt pool dynamics control, preparing a single-phase BCC structure coating with both high strength and toughness and excellent wear resistance, significantly improving the service reliability of aerospace components under extreme conditions.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite material preparation and laser surface modification technology, and relates to a high wear-resistant, refractory, high entropy alloy coating with gradient structure rare earth nitride coated ceramic solid solution strengthening and its preparation method. In particular, it relates to a method of using the sol-gel method to construct core-shell structure precursor powder and combining it with pre-alloy powder to prepare a high-performance gradient coating. Background Technology

[0002] Refractory high-entropy alloys, as a new generation of high-performance metallic materials, are characterized by their high mixing entropy system (ΔS > 1.5R) and simple phase composition of a single-phase BCC structure. Leveraging unique lattice distortion effects and hysteretic diffusion characteristics, these alloys have successfully broken through the strength-toughness balance limit of traditional alloys, exhibiting excellent high-temperature stability, creep resistance, and superior mechanical properties, making them ideal materials for core components serving in extreme environments such as aerospace engine blades and nuclear reactor components. With the advancement of laser cladding technology, the metallurgical bonding of high-entropy alloy coatings to substrate surfaces using high-energy laser beams provides an efficient path for surface strengthening and lifespan extension of critical components. However, as spacecraft evolve towards high thrust-to-weight ratios and long-term service, the performance bottlenecks of traditional single-layer homogeneous refractory high-entropy alloy coatings under complex operating conditions are becoming increasingly prominent. Specifically, the substrate hardness is relatively insufficient. Under ultra-high-speed airflow scouring and severe friction and wear environments, due to the large hardness difference and mismatch in thermal expansion coefficients between the coating and the substrate, brittle spalling easily occurs, leading to unsatisfactory service life of components and increased maintenance costs and safety risks.

[0003] To further improve the mechanical and wear-resistant properties of coatings, researchers generally tend to introduce ceramic particles such as WC, B4C, and TiN, and use the high-temperature molten pool of laser cladding technology to promote the uniform distribution or direct decomposition of ceramic particles, attempting to achieve intrinsic strengthening of the original alloy material by directly adding new ceramic phases externally or synthesizing them in situ.

[0004] Existing technology CN 113493913 A discloses a method for reinforcing a high-entropy alloy cladding layer with WC ceramic particles, which utilizes synchronous powder feeding to directly add micron-sized WC particles to the high-entropy alloy. However, due to the significant difference in thermal expansion coefficients between the ceramic phase and the metal matrix, huge residual thermal stress is generated at the interface during rapid laser solidification, leading to reduced material bonding strength and easy initiation of microcrack propagation and particle spalling. Furthermore, existing technologies often employ mechanical mixing of elemental metal powders in conjunction with direct injection of ceramic particles. Due to the lack of effective molten pool flow control, lightweight ceramic particles are prone to floating and agglomeration, resulting in severe compositional segregation. Existing technology CN 112962095 A discloses a method and application for preparing a ceramic-reinforced laser cladding coating of a refractory high-entropy alloy on a titanium alloy surface. Although it achieves TiN reinforcement, poor powder flowability and insufficient molten pool kinetics lead to local solute supersaturation, resulting in the precipitation of brittle silicide or nitride second phases. These hard and brittle phases, together with metallurgical defects such as pores and cracks, constitute stress concentration sources, causing the coating to suffer a sharp decline in fracture toughness and spalling resistance when subjected to high-frequency vibration and thermal shock from aero-engine blades.

[0005] Therefore, there is an urgent need to develop a novel coating structure design and powder modification paradigm. On the one hand, it is necessary to overcome the stress bottleneck of traditional single-layer coatings by using gradient structure design to smooth the thermal expansion difference between the substrate and the functional layer, thereby suppressing the formation of cold cracks. On the other hand, while ensuring excellent powder flowability, it is necessary to introduce key elements that can actively regulate the molten pool dynamics, achieving full solid solution and homogeneous distribution of ceramic atoms within an extremely short laser action window. While effectively avoiding the precipitation of hard and brittle phases, the coating's toughness, wear resistance, and service reliability can be synergistically improved through refined microstructure control and gradient transition of macrostructure, thus meeting the stringent requirements of aerospace hot-end components for surface protection technology. Summary of the Invention

[0006] In view of this, to address the problems of high hardness and easy cracking of traditional refractory high-entropy alloy coatings, as well as poor wettability of the ceramic reinforcing phase, which makes it difficult to synergistically improve the coating's strength, toughness, wear resistance, and service reliability, thus affecting its application scenarios, this invention provides a gradient-structured rare-earth nitride-coated ceramic solid solution reinforced high-wear-resistant refractory high-entropy alloy coating and its preparation method. A nano-YN coating layer is constructed on the Si3N4 surface using the sol-gel method, combined with pre-alloyed powder and gradient structure design. The YN coating layer improves interfacial wettability, and the active Y element reduces the melt surface tension, inducing strong Marangoni convection and promoting the full thermal decomposition and atomic-level uniform diffusion of Si3N4. Through compositional regulation, the decomposed N atoms and Si atoms enter the TiZrNbMo lattice through interstitial and substitutional solid solution reinforcement mechanisms, respectively, forming a stable single BCC solid solution phase. Combined with the gradient distribution of the "base layer-transition layer-wear-resistant functional layer," thermal stress mismatch is effectively alleviated, porosity and crack defects are completely eliminated, and strength and toughness are synergistically optimized with wear resistance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a rare earth nitride-coated ceramic solid solution reinforced high wear-resistant refractory high-entropy alloy coating includes the following steps:

[0009] S1. Substrate Pretreatment: The surface of the titanium alloy substrate is ground, cleaned and dried to remove oxide scale and oil stains. Specifically, after the titanium alloy substrate is cut into appropriately sized samples, its surface is subjected to pretreatment procedures such as sanding, ultrasonic cleaning and drying in a drying oven to make the substrate surface smooth and remove impurities such as oxide layer, oil stains and abrasive debris, so as to ensure good adhesion between the coating and the substrate.

[0010] S2. Preparation of precursor powder: Using the sol-gel method with citric acid as a chelating agent, micron-sized Si3N4 powder was dispersed in a 0.05-0.2 mol / L soluble yttrium salt solution at a solid-liquid ratio of 38.5 g / L. The pH value was adjusted to 3-5, and the mass ratio of Si3N4 powder to soluble yttrium salt was controlled to be 1:0.8-1. After magnetic stirring, ultrasonic dispersion, gelation, and drying, the powder was calcined at 700-900 ℃ in an ammonia or nitrogen-hydrogen mixed atmosphere to generate a YN nano-coating layer in situ on the surface of Si3N4, thus obtaining YN@Si3N4 composite powder.

[0011] S3. Gradient Mixing Powder Preparation: Spherical pre-alloyed TiZrNbMo high-entropy alloy powder prepared by gas atomization was selected as the matrix material. YN@Si3N4 composite powders with different mass ratios from step S2 were weighed and mixed using a low-speed intermittent ball milling process. Three sets of mixed powders with low, medium, and high contents were prepared as the base layer, transition layer, and wear-resistant functional layer, respectively. The mixing process was carried out under argon protection to ensure that the powder was free from oxidation and that the core-shell structure remained intact. The powders were then dried and sealed for later use. The content of YN@Si3N4 was 0~3.0 wt.%.

[0012] S4. Preparation of gradient coating by laser cladding: Multi-layer gradient cladding is performed on the substrate surface after step S1 using laser cladding equipment; first, a base layer with low YN@Si3N4 content is clad to ensure metallurgical bonding, then a transition layer with medium content is clad to relieve thermal stress, and finally a wear-resistant layer with high content is clad; the high energy density of the laser is used to fully thermally decompose YN@Si3N4 and achieve uniform solid solution of Si, N and Y atoms, thus preparing a gradient high-entropy alloy coating without cracks or ceramic phase precipitation.

[0013] Coating phase characterization and performance determination: The prepared gradient coating was cut, polished, and its phase composition was analyzed by XRD to confirm a single BCC structure and the absence of brittle phase precipitation. The cross-sectional morphology was observed by SEM to verify the compactness and defect-free characteristics of the gradient structure. The microhardness gradient distribution was tested, and its wear resistance was evaluated using a tribological testing machine.

[0014] Furthermore, in step S1, the sandpaper used to polish the titanium alloy substrate is 180-mesh and 400-mesh silicon carbide coarse sandpaper; the substrate drying temperature is set to 60~100 ℃, and the drying time is 1~3 h.

[0015] Furthermore, in step S2, the Si3N4 particle size in the precursor powder is 1 ~ 3 µm, and the thickness of the in-situ generated YN coating layer is 30 ~ 50 nm.

[0016] Furthermore, the parameters for the sol stage in step S2 are controlled as follows: yttrium nitrate hexahydrate is used as the solute, and the concentration range after dissolution is 0.05 ~ 0.2 mol / L; anhydrous ethanol or deionized water is used as the solvent, citric acid is added as a chelating agent, and the pH value is adjusted to 3 ~ 5; the mass ratio of Si3N4 powder to yttrium nitrate is 1:0.8 ~ 1:1.

[0017] Furthermore, the ultrasonic dispersion process in step S2 is as follows: magnetic stirring for 2 to 4 hours, followed by treatment at an ultrasonic frequency of 40 to 60 kHz for 30 to 60 minutes; the calcination process is as follows: drying at 80 to 100 ℃ to form a gel powder, followed by calcination at 700 to 900 ℃ for 2 to 4 hours in an ammonia or nitrogen-hydrogen mixed atmosphere.

[0018] Furthermore, step S3 employs a low-speed intermittent ball milling process: the ball mill speed is 180-220 r / min; the ball-to-material ratio is 3:1; and the total mixing time is 3-5 h. A bidirectional rotation method is used: after rotating forward for 8-12 min, pause for 5-7 min, then rotate in the reverse direction for 8-12 min, and this cycle is repeated. This process aims to prevent powder oxidation and damage to the core-shell structure of YN@Si3N4.

[0019] Furthermore, in step S3, the particle size of the TiZrNbMo pre-alloyed powder is 45 ~ 150 µm, and its component ratio ranges as follows: Ti, Zr, Nb, and Mo are all 23 ~ 27 at.%.

[0020] Furthermore, the proportions of the gradient-mixed powders in step S3 are designed as follows: the amount of YN@Si3N4 added in the base layer powder is 0~0.5 wt.%; the amount of YN@Si3N4 added in the transition layer powder is 1.0~1.5 wt.%; and the amount of YN@Si3N4 added in the wear-resistant functional layer powder is 2.0~3.0 wt.%.

[0021] Furthermore, the laser cladding experimental parameters in step S4 are as follows: laser power 800 ~ 1400 W, scanning speed 3 ~ 7 mm / s, powder feeding rate 2 ~ 4 r / min, spot diameter 1 ~ 3 mm, overlap rate 40 ~ 60%, and the protective gas is high-purity argon with a flow rate of 15 ~ 25 L / min.

[0022] Furthermore, the XRD test conditions in step S5 are as follows: radiation source Cu-Kα, power 12 kW, scanning range 10°~90°, scanning speed 5° / min. The etching solution ratio is HNO3 : HF : HCl : H2O = 2.5 : 1 : 1.5 : 9.5.

[0023] Furthermore, the test conditions for surface microhardness in step S5 are as follows: random sampling, and the average value of seven sampling points for each sample is taken as the surface hardness of the coating.

[0024] Furthermore, the test conditions for the microhardness of the cross section in step S5 are as follows: the load is 2 N, the holding time is 10 s, the measurement point interval is 0.2 mm, and three parallel tests are performed in the horizontal direction at each depth. The average value is taken as the microhardness value at that cross section location.

[0025] Preferably, the test conditions for wear resistance in step S5 are: load of 10 N, rotation speed of 400 r / min, wear time of 30 min, friction radius of 3 mm, and friction pair of Si3N4 spheres with a diameter of 6 mm.

[0026] The gradient-structured rare-earth nitride-coated ceramic solid solution reinforced high-wear-resistant refractory high-entropy alloy coating prepared by the above-mentioned method is characterized by a gradient structure consisting of a base layer, a transition layer, and a wear-resistant functional layer, arranged sequentially from the substrate surface outwards. The base layer is either a pure TiZrNbMo refractory high-entropy alloy layer or a TiZrNbMo refractory high-entropy alloy layer with trace amounts of YN@Si3N4 composite powder, used to achieve high-strength metallurgical bonding with the substrate. The transition layer is a TiZrNbMo refractory high-entropy alloy layer with a moderate amount of YN@Si3N4 composite powder, used to alleviate thermal stress mismatch. The wear-resistant functional layer is a TiZrNbMo refractory high-entropy alloy layer with a high amount of YN@Si3N4 composite powder, used to provide high hardness and wear resistance.

[0027] Furthermore, the atomic percentage of each component in the TiZrNbMo refractory high-entropy alloy matrix is ​​23.00 ~ 27.00 at.%; the mass percentage of the YN@Si3N4 composite powder in each layer shows a gradient increasing distribution: 0 ~ 0.5 wt.% in the base layer; 1.0 ~ 1.5 wt.% in the transition layer; and 2.0 ~ 3.0 wt.% in the wear-resistant layer.

[0028] Furthermore, the above-mentioned high wear-resistant refractory high-entropy alloy coatings are used in the surface protection of aerospace engine blades and erosion-resistant components of supersonic aircraft.

[0029] A titanium alloy having a surface loaded with a gradient structure rare earth nitride-coated ceramic solid solution reinforced, highly wear-resistant, refractory, and high-entropy alloy coating.

[0030] The beneficial effects of this invention are as follows:

[0031] 1. The method for preparing a high-wear-resistant, refractory, high-entropy alloy coating for ceramic solid solution reinforcement using rare-earth nitrides disclosed in this invention constructs a nanoscale YN coating layer on the surface of micron-sized Si3N4 using a sol-gel method, forming a core-shell structure. This effectively shields the van der Waals forces and electrostatic attraction between ceramic powders, solving the problems of easy agglomeration and adhesion of traditional ceramic powders. More importantly, this invention uses spherical pre-alloyed TiZrNbMo high-entropy alloy powder instead of traditional elemental powder mixtures, and combines this with a low-speed ball milling process to achieve uniform mixing of the reinforcing phase and the matrix without damaging the YN@Si3N4 core-shell structure. This combination strategy of core-shell YN@Si3N4 ceramic + spherical pre-alloyed TiZrNbMo ensures the continuity of powder flow and the uniformity of the molten pool composition during laser cladding, avoiding coating quality fluctuations caused by powder feeding pulsation from the source.

[0032] 2. The rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant, refractory, high-entropy alloy coating disclosed in this invention utilizes the strong surface activity of rare-earth element Y to significantly reduce the surface tension of the high-temperature melt, inducing strong Marangoni convection driven by the surface tension gradient within the molten pool. This intense liquid-phase turbulence effectively counteracts the upward floating tendency of lightweight ceramic particles, promoting the rapid atomic-level diffusion and homogenization of Si3N4 decomposition products within an extremely short laser solidification window. Combined with the excellent wettability of the YN coating layer, this invention successfully avoids local solute supersaturation, eliminates the precipitation of hard and brittle second phases such as silicides and nitrides, and obtains a pure single-phase BCC solid solution structure.

[0033] 3. The method for preparing a rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant refractory high-entropy alloy coating disclosed in this invention constructs a gradient structure of a substrate layer, a transition layer, and a wear-resistant functional layer. By gradually increasing the content of YN@Si3N4 (0~3.0 wt.%) from the inside out, a smooth transition in the coating's coefficient of thermal expansion and hardness is achieved. The substrate layer establishes a high-strength metallurgical bond with the titanium alloy substrate, the transition layer effectively releases the residual thermal stress generated by rapid laser solidification, and the wear-resistant functional layer provides ultimate surface protection performance. This biomimetic gradient design significantly improves the coating's fracture toughness and anti-stripping ability, solving the problem of brittle spalling that easily occurs in single-component coatings under ultra-high-speed impact.

[0034] 4. The rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant, refractory, high-entropy alloy coating disclosed in this invention achieves a dual strengthening effect of interstitial N-atom solid solution and substitutional Si-atom solid solution. Combined with the large lattice distortion energy generated by the active element Y, this significantly improves the intrinsic hardness of the coating. Simultaneously, Y possesses extremely strong oxo and sulfide affinity, preferentially capturing impurities such as O and S in the molten pool to form high-melting-point compounds, thus purifying grain boundaries and eliminating porosity sources. Furthermore, the in-situ generated YN and decomposed particles serve as effective heterogeneous nucleation sites, significantly refining the coating grains. Through the synergistic effect of gradient structure, solid solution strengthening, and grain refinement, the resulting coating exhibits both high hardness and high toughness, fully meeting the reliability requirements of aerospace hot-end components under harsh service environments.

[0035] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0037] Figure 1 These are phase and morphology characterization images of the titanium alloy substrate and YN@Si3N4 composite precursor powder prepared in Example 1 of this invention. Figure 1 (a) is the XRD pattern of the titanium alloy substrate; Figure 1 (b) XRD pattern of YN@Si3N4 composite precursor powder; Figure 1 (c) Surface morphology of titanium alloy substrate; Figure 1 (d) shows the surface morphology of the precursor powder and the corresponding elemental EDS surface scan images;

[0038] Figure 2 The microstructure and EDS elemental distribution of the TiZrNbMo alloy powder and YN@Si3N4 mixed powder prepared in Example 1 of this invention are shown in Figure 1. Figure 2 (a) shows the microstructure of the mixed powder; Figure 2 (b) is Figure 2 (a) A magnified view of the area within the yellow box; the rest are EDS surface scan images of each element.

[0039] Figure 3 The XRD patterns are those of the gradient structure high-entropy alloy coatings prepared in Examples 1 and 2 of this invention.

[0040] Figure 4(a), (b), and (c) are, respectively, surface morphology diagrams of the high-entropy alloy coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0041] Figure 5 (a), (b), and (c) are cross-sectional morphology diagrams of the high-entropy alloy coatings prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention, respectively.

[0042] Figure 6 The images show the microhardness of the coatings prepared in Examples 1, 2, 1, and 2 of this invention, and the surface of Comparative Example 3. Figure 6 (a) is a comparison chart of average surface hardness; Figure 6 (b) is a comparison diagram of cross-sectional hardness;

[0043] Figure 7 These are test images of the tribological properties of the coatings prepared in Examples 1, 2, 1, and 2 of this invention, and the surface of Comparative Example 3. Figure 7 (a) is a comparison chart of average friction coefficients; Figure 7 (b) is a comparison chart of wear rates;

[0044] Figure 8 (a), (b), (c), and (d) are, in order, surface wear morphology diagrams of the coatings prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention. Detailed Implementation

[0045] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] Example 1

[0047] This embodiment provides a method for preparing a gradient structure rare earth nitride-coated ceramic-reinforced refractory high-entropy alloy coating, the specific steps of which are as follows:

[0048] S1. Substrate pretreatment: The TiZrAlV titanium alloy substrate sheet was cut into 50 mm × 15 mm × 10 mm samples using a wire EDM machine. The samples were then polished sequentially with 180-grit and 400-grit silicon carbide sandpaper to remove surface oxide scale and increase surface roughness to improve laser absorption. After ultrasonic cleaning with anhydrous ethanol for 15 min, the samples were dried in an 80 ℃ oven for 2 h for later use.

[0049] S2 and YN@Si3N4 core-shell precursor powders were prepared using a sol-gel method. Yttrium nitrate hexahydrate was dissolved in anhydrous ethanol to prepare a 0.1 mol / L precursor solution. Citric acid was added as a chelating agent to adjust the pH to 4. α-Si3N4 ceramic powder with a particle size of 1–3 µm was added to the solution, maintaining a Si3N4 to yttrium nitrate mass ratio of 1:1. The mixture was ultrasonically dispersed at 50 kHz for 45 min under magnetic stirring to form a homogeneous suspension. The mixture was stirred and evaporated to dryness at 90 °C until a gel was formed, followed by drying in an oven at 100 °C for 12 h to obtain a dry gel powder. Finally, the powder was placed in a tube furnace and calcined at 800 °C for 3 h under an NH3 atmosphere, followed by furnace cooling to obtain YN@Si3N4 composite powder with a 40 nm thick YN nanolayer coated on the surface.

[0050] S3. Gradient-mixed powder formulation: Spherical Ti, Zr, Nb, and Mo high-entropy alloy powders with a particle size of 65 µm were selected as the matrix to ensure microscopic uniformity of composition. Three sets of gradient powders were designed for the base layer, transition layer, and wear-resistant functional layer, respectively. The three sets of powders were placed in a planetary ball mill. To protect the YN coating layer from damage, a low-speed intermittent ball milling process was adopted: the milling speed was 180 r / min, the ball-to-powder ratio was 3:1, and the milling jar was filled with argon gas for protection. The cycle program was set as follows: forward rotation for 10 min, pause for 5 min, reverse rotation for 10 min, with a total effective milling time of 2 h. After drying, the powders were sealed and stored for later use. The YN@Si3N4 content in the base layer powder was 0.5 wt.%; the YN@Si3N4 content in the transition layer powder was 1.5 wt.%; and the YN@Si3N4 content in the wear-resistant functional layer powder was 3.0 wt.%.

[0051] S4. Laser cladding gradient coating preparation: Multi-layer cladding is performed on the substrate surface treated in S1 using laser cladding equipment. The process parameters for preparing the base layer are: laser power 1000 W, scanning speed 5 mm / s; for the transition layer, laser power 1200 W, scanning speed 5 mm / s; and for the wear-resistant functional layer, laser power 1400 W, scanning speed 4 mm / s. An orthogonal scanning strategy is used between layers, with an overlap rate of 50%. The interlayer cooling time is controlled within 30 seconds to utilize residual heat and reduce cracking. After cladding, the sample is cut, inlaid, ground, and polished.

[0052] S5. Characterization and Testing: Phase analysis was performed using XRD, and cross-sectional morphology and elemental distribution were observed using SEM. Microhardness gradient test (load 2 N, hold for 10 s) and friction and wear test (load 10 N, rotation speed 400 r / min, time 30 min, with Si3N4 balls in the grinding pair) were conducted.

[0053] Example 2

[0054] The only difference between this embodiment and Embodiment 1 is the adjustment of the gradient ratio and laser parameters to verify the process window. Regarding the gradient design, the substrate layer is -0.0 wt.% YN@Si3N4, the transition layer is -1.0 wt.% YN@Si3N4, and the wear-resistant layer is -2.5 wt.% YN@Si3N4. For the laser parameters, the power is uniformly set to 1200 W, the scanning speed to 6 mm / s, and the overlap rate to 45%. The remaining precursor concentrations and ball milling processes are the same as in Embodiment 1.

[0055] Comparative Example 1 (No Gradient Structure)

[0056] The only difference between this comparative example and Example 1 is that the gradient ratio structure was not set. Instead, the three-layer gradient was entirely composed of a 3.0 wt.% YN@Si3N4 composite powder, and a single-layer multi-pass cladding was performed directly on a titanium alloy substrate to prepare a single-component coating of the same thickness. All other parameters and conditions were the same as in Example 1. Observational results showed that during the laser cladding cooling process, due to the thermal stress mismatch between the coating and the substrate, visible cracks were observed at the interface between the coating and the substrate, extending to the coating surface.

[0057] Comparative Example 2 (no core-shell coating, powder was only mechanically mixed)

[0058] The only difference between this comparative example and Example 1 is that the sol-gel coating is omitted in step S2; instead, the original micron-sized Si3N4 ceramic particles are directly mechanically mixed with TiZrNbMo pre-alloyed powder. All other process parameters are the same as in Example 1. Observational results show that despite the use of a gradient structure, due to the poor wettability of Si3N4 with metals and the lack of Y-induced Marangoni convection, cross-sectional SEM revealed severe agglomeration of Si3N4 particles. Micropores appeared around some of the undecomposed large ceramic particles, and the coating density was significantly lower than in Example 1.

[0059] Comparative Example 3 (Substrate Control)

[0060] The difference between this comparative example and Example 1 is that the TiZrAlV titanium alloy substrate treated in step S1 was directly used for hardness and wear resistance testing.

[0061] Example Effect Verification and Discussion

[0062] By comparing the test data of the above embodiments with those of the comparative examples, the significant advantages of the present invention are verified:

[0063] Figure 1 Characterization of the titanium alloy substrate and the YN@Si3N4 core-shell composite precursor powder prepared by the sol-gel method is presented. Figure 1(b) XRD pattern and Figure 1 The EDS surface scan image (d) visually demonstrates that the YN nanolayer was successfully and uniformly coated on the surface of micron-sized Si3N4 particles, forming a stable core-shell structure.

[0064] Figure 2 The images show the microstructure and elemental distribution of the mixture of spherical TiZrNbMo alloy powder and YN@Si3N4 composite powder. The images demonstrate that, using a low-speed ball milling process, the elements are distributed extremely uniformly in the mixed powder without damaging the core-shell structure. This effectively shields the van der Waals forces between traditional ceramic powders, solving the technical problems of easy agglomeration of ceramic particles and powder feeding pulsation.

[0065] Figure 3 The XRD patterns of the gradient coatings prepared in Examples 1 and 2 were compared. The results confirmed that the coating structure of the present invention is a pure single BCC solid solution structure, and no diffraction peaks of residual Si3N4 or other hard and brittle second phases were detected. This demonstrates that the strong Marangoni convection induced by the active element Y significantly promotes the full thermal decomposition and atomic-level uniform diffusion of Si3N4 during the rapid solidification period, successfully avoiding phase segregation caused by local solute supersaturation.

[0066] Figure 4 The surface morphology of the coatings in Example 1, Comparative Example 1 with no gradient structure, and Comparative Example 2 with a gradient but no coating were compared, visually demonstrating the advantages of the smooth, dense, and crack-free surface of the coating in Example 1. A comparison of the surface morphology of coatings prepared under different processes was also shown. Observations revealed that... Figure 4 Example 1, as shown in Figure a, exhibits a dense surface structure without any visible cracks, while Comparative Example 1 without a gradient structure and Comparative Example 2 without a coating structure show obvious microcracks and porosity defects, respectively. This fully verifies the synergistic effect of the gradient structure design in alleviating phase transition thermal stress and the YN coating layer in eliminating defects.

[0067] Figure 5 The cross-sectional microstructures of the coatings in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Example 1 exhibits a clear and tight metallurgical bonding gradient delamination characteristic. In contrast, Comparative Example 1 shows through-cracks due to thermal expansion coefficient mismatch, while Comparative Example 2 suffers from severe precursor powder segregation and porosity defects due to poor wettability of the ceramic phase. This comparison demonstrates that the YN coating improves interfacial wettability and, in conjunction with the gradient design, alleviates residual stress.

[0068] Figure 6 The images show the surface and cross-sectional microhardness distribution of the coatings in each embodiment and comparative example. Tests show that Example 1 exhibits a step-like increase in hardness from the substrate to the surface, with the highest average surface hardness of 674.3 HV. 0.2This gentle hardness gradient avoids stress concentration caused by abrupt changes in hardness, demonstrating the effectiveness of the substrate-transition layer-wear-resistant functional layer composition design in achieving coating strength and toughness control.

[0069] Figure 7 The average coefficient of friction and volumetric wear rate of the coatings in each embodiment and comparative example were compared. The results show that Example 1 has the lowest coefficient of friction and the lowest wear rate, and its wear resistance is significantly better than all comparative examples. This is due to the dual strengthening effect of interstitial solid solution of N atoms and substitutional solid solution of Si atoms, combined with the huge lattice distortion energy generated by the active element Y, which significantly improves the intrinsic hardness and service reliability of the coating.

[0070] Figure 8 The wear morphology of the coating surfaces in Example 1 and various comparative examples is shown. Example 1 exhibits a continuous oxide glaze layer with the shallowest wear marks and no peeling, while the other comparative examples show severe plastic deformation and deep, long furrows. This further verifies that, through the synergistic effect of solid solution strengthening and grain refinement strengthening, the coating of this invention possesses both extremely high hardness and wear resistance, meeting stringent wear resistance requirements.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a gradient-structured rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant refractory high-entropy alloy coating, characterized in that, Includes the following steps: S1. Substrate pretreatment: Grinding, cleaning and drying the titanium alloy substrate to remove oxide scale and oil stains; S2. Preparation of precursor powder: Using the sol-gel method with citric acid as a chelating agent, micron-sized Si3N4 powder was dispersed in a 0.05-0.2 mol / L soluble yttrium salt solution at a solid-liquid ratio of 38.5 g / L. The pH value was adjusted to 3-5, and the mass ratio of Si3N4 powder to soluble yttrium salt was controlled to be 1:0.8-1. After magnetic stirring, ultrasonic dispersion, gelation, and drying, the powder was calcined at 700-900 ℃ in an ammonia or nitrogen-hydrogen mixed atmosphere to generate a YN nano-coating layer in situ on the surface of Si3N4, thus obtaining YN@Si3N4 composite powder. S3. Gradient Mixing Powder Preparation: Spherical pre-alloyed TiZrNbMo high-entropy alloy powder prepared by gas atomization was used to mix with YN@Si3N4 composite powder obtained in step S2, whose content increased from the inside to the outside, through low-speed ball milling. This produced three mixed powders for the base layer, transition layer, and wear-resistant functional layer, respectively, and each was then dried. The content of YN@Si3N4 was 0~3.0 wt.%. S4. Laser cladding gradient preparation: Using a laser cladding device, the base layer, transition layer and wear-resistant functional layer prepared in step S3 are sequentially clad on the surface of the substrate after step S1. The layers are densely bonded by laser remelting to prepare a gradient structure high-entropy alloy coating without ceramic phase precipitation.

2. The method for preparing the high wear-resistant, refractory, high-entropy alloy coating as described in claim 1, characterized in that, In step S2, the yttrium precursor solution is yttrium nitrate hexahydrate with a concentration range of 0.05 ~ 0.2 mol / L after dissolution. Anhydrous ethanol or deionized water is used as the solvent, and citric acid is added as a chelating agent to adjust the pH to 3 ~ 5. The mass ratio of Si3N4 powder to yttrium nitrate is 1:0.8~1. The magnetic stirring time is 2 ~ 4 h, and the ultrasonic dispersion process is carried out at an ultrasonic frequency of 40 ~ 60 kHz for 30 ~ 60 min. The drying and high-temperature calcination process involves drying at 80 ~ 100 ℃ to form a gel powder, followed by high-temperature calcination in an ammonia or nitrogen-hydrogen mixed atmosphere at a calcination temperature of 700 ~ 900 ℃ for 2 ~ 4 h.

3. The method for preparing the high wear-resistant, refractory, high-entropy alloy coating as described in claim 2, characterized in that, In step S2, the particle size of Si3N4 ceramic powder ranges from 1 to 3 µm, and the thickness of the YN modified nanocoating layer ranges from 30 to 50 nm.

4. The method for preparing the high wear-resistant, refractory, high-entropy alloy coating as described in claim 3, characterized in that, The low-speed ball milling parameters in step S3 are as follows: ball mill speed is 180 ~ 220 r / min, ball-to-material ratio is 3:1, and mixing time is 3 ~ 5 h; bidirectional rotation is adopted: after rotating forward for 8 ~ 12 min, pause for 5 ~ 7 min, then rotate in the reverse direction for 8 ~ 12 min, and so on until the set ball milling time is reached; the ball mill jar is filled with high-purity argon gas for protection to prevent powder oxidation.

5. The method for preparing the high wear-resistant, refractory, high-entropy alloy coating as described in claim 4, characterized in that, In step S3, the particle size range of the TiZrNbMo pre-alloyed powder is 45~150 µm, and the composition ratio range is 23~27 at.% for Ti, Zr, Nb, and Mo.

6. The method for preparing the high wear-resistant, refractory, high-entropy alloy coating as described in claim 5, characterized in that, The multi-layer gradient cladding in step S4 is as follows: First, the YN@Si3N4 content in the base layer powder is 0 ~ 0.5 wt.%; then, the YN@Si3N4 content in the transition layer powder is 1.0 ~ 1.5 wt.%; finally, the YN@Si3N4 content in the wear-resistant functional layer powder is 2.0 ~ 3.0 wt.%.

7. The method for preparing the high wear-resistant refractory high-entropy alloy coating as described in claim 6, characterized in that, The laser cladding process parameters for step S4 are as follows: laser power 800 ~ 1400 W; scanning speed 3 ~ 7 mm / s; powder feeding rate 2 ~ 4 r / min; spot diameter 1 ~ 3 mm; overlap rate 40 ~ 60%; and the protective gas is high-purity argon with a flow rate of 15 ~ 25 L / min.

8. A gradient-structured rare-earth nitride-coated ceramic solid solution-strengthened high-wear-resistant, refractory-high-entropy alloy coating prepared by the preparation method of any one of claims 1 to 7, wherein the high-wear-resistant, refractory-high-entropy alloy coating has a gradient structure consisting of a base layer, a transition layer, and a wear-resistant functional layer arranged sequentially from the surface of the substrate outwards, wherein... The base layer is a pure TiZrNbMo refractory high-entropy alloy layer or a TiZrNbMo refractory high-entropy alloy layer with trace amounts of YN@Si3N4 composite powder, used to achieve high-strength metallurgical bonding with the substrate; the transition layer is a TiZrNbMo refractory high-entropy alloy layer with a medium content of YN@Si3N4 composite powder, used to alleviate thermal stress mismatch; the wear-resistant functional layer is a TiZrNbMo refractory high-entropy alloy layer with a high content of YN@Si3N4 composite powder, used to provide high hardness and wear resistance.

9. The high wear-resistant, refractory, high-entropy alloy coating as described in claim 8, characterized in that, The high wear-resistant, refractory, high-entropy alloy coating has a single-phase BCC structure, with no Si3N4 residues or hard and brittle second phases such as silicides and nitrides precipitated; Si atoms exist in the form of substitutional solid solution, and N atoms occupy the interstitial spaces of the crystal lattice in the form of interstitial solid solution.

10. The application of the high wear-resistant refractory high-entropy alloy coating as described in claim 9 in the surface protection of aerospace engine blades and erosion-resistant components of supersonic aircraft.

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