A high-entropy alloy wear-resistant coating with BCC phase transformation strengthening and self-lubricating properties and its preparation method

Abstract

This invention discloses a high-entropy alloy wear-resistant coating with BCC phase transformation strengthening and self-lubricating properties, and its preparation method. The atomic percentage composition of the high-entropy alloy wear-resistant coating is Fe 22.5%, Co 22.5%, Ni 10%, Cr 35%, and Al 10%, with a BCC phase structure. It is prepared by laser cladding of metal powder with the above-mentioned composition onto the surface of a 45# steel substrate. The coating has a dense structure and good metallurgical bonding. Without adding any ceramic particles, the microhardness reaches 610 HV, and the average coefficient of friction is as low as 0.184. This invention provides a low-cost, high-performance technical solution for wear-resistant protection of mechanical parts surfaces based on a multiple strengthening mechanism dominated by BCC phase transformation, synergistic effect of lattice distortion and substructure, and in-situ oxidation self-lubrication.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a high-entropy alloy wear-resistant coating and a method for preparing the high-entropy alloy coating. Background Technology

[0002] High-entropy alloys are novel metallic materials composed of five or more main elements in equiatomic or near-equiatomic ratios, with each element comprising 5%-35% of the total atomic mass. This unique design endows them with a thermodynamic high-entropy effect, a kinetic hysteresis diffusion effect, a structural lattice distortion effect, and a "cocktail" effect in terms of properties. Under the synergistic effect of these factors, high-entropy alloys exhibit high strength, high hardness, excellent wear resistance, and corrosion resistance, making them promising for applications in aerospace, marine engineering, and other fields.

[0003] To overcome the problems of high cost and difficult processing of bulk high-entropy alloys, researchers have focused on preparing them as surface coatings. Laser cladding technology has become an ideal method for preparing high-entropy alloy coatings due to its advantages such as fast heating and cooling rates, dense cladding layers, metallurgical bonding with the substrate, and small heat-affected zone. The literature Wang K, Gao P, et al. Surface & Coatings Technology, 2025, discloses a method for preparing a dense high-entropy alloy coating with good bonding to the substrate on the surface of steel using laser cladding technology, achieving a hardness more than three times that of the substrate.

[0004] FeCoNiCrAl series high-entropy alloys have attracted much attention due to their excellent balance of strength, plasticity, oxidation resistance, and wear resistance. Among these, Cr has a decisive influence on the coating phase structure and mechanical properties: it can form a dense passivation film to improve corrosion resistance, and it can also act as a BCC structure-forming element to change phase selectivity, directly affecting the coating hardness and wear resistance. The literature He ZH, Dong YC, et al. Journal of Alloys and Compounds, 2025, discloses a formula for FeCoNiMnAl... 0.5 Cr x The high-entropy alloy coating effectively improves the passivation performance of the coating by controlling the Cr content, and obtains an FCC / BCC dual-phase structure. At the same time, the severe lattice distortion that appears significantly enhances the strength and hardness of the material.

[0005] Current research on FeCoNiCrAl-based high-entropy alloy coatings largely focuses on equiatomic ratios or narrow compositional ranges, with insufficient systematic study of the microstructure and property evolution under high Cr content. Alloy composition is a fundamental factor affecting the wear resistance of high-entropy alloy coatings; however, current composition design still relies heavily on experience and trial-and-error methods, and the intrinsic mechanism between Cr content and coating microstructure and wear resistance needs further elucidation. Therefore, developing novel high-wear-resistant coatings through precise control of Cr content has significant research value and engineering implications. Summary of the Invention

[0006] The purpose of this invention is to provide a novel wear-resistant coating material with high hardness, low wear rate, and stable service performance, which is obtained by designing a specific non-equiatomic ratio composition and preparing it using laser cladding technology.

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

[0008] A high-entropy alloy coating with good wear resistance is characterized in that the chemical composition of the coating consists of the following elements in atomic percentage: Fe 22.5%, Co 22.5%, Ni 10%, Cr 35%, Al 10%.

[0009] The present invention also provides a method for preparing the above-mentioned high-entropy alloy coating with good wear resistance, comprising the following steps:

[0010] Step 1, Substrate pretreatment: Using 45# steel as the substrate, clean and grind the surface of the substrate to remove oil, rust and oxide scale, and clean it with anhydrous ethanol, then dry it for later use.

[0011] Step 2, Alloy powder preparation: Weigh high-purity metal powder according to the atomic percentages of Fe 22.5 at.%, Co 22.5 at.%, Ni 10 at.%, Cr 35 at.%, and Al 10 at.%, and mix them thoroughly using a ball milling process to obtain alloy powder;

[0012] Step 3, Laser Cladding: Using synchronous powder feeding laser cladding technology, the alloy powder mixed in Step 2 is clad onto the surface of the 45# steel substrate after pretreatment in Step 1, and a coating is formed by multiple overlapping layers; the process parameters of laser cladding are: laser power 900W, scanning speed 6mm / s, spot diameter 3mm, powder feeding speed 20g / min, protective gas is argon, and gas flow rate is 15L / min;

[0013] Step 4, Post-processing: After the cladding is completed, the coating is naturally cooled to room temperature to obtain the high-entropy alloy coating with good wear resistance.

[0014] Furthermore, the purity of the high-purity metal powder in step 2 is greater than 99.5%, and the powder particle size is 50-150μm.

[0015] Furthermore, in step 3, the coating thickness formed by laser cladding is 1.0 mm, and the overlap rate of multiple overlaps is controlled between 30% and 50%.

[0016] The beneficial effects of this invention are:

[0017] This invention limits the alloy composition to Fe. 22.5 Co 22.5 Ni 10 Cr 35 Al 10 By combining an optimized laser cladding process (900W, 6mm / s), a high-entropy alloy coating with a dense microstructure and good metallurgical bonding with the substrate was prepared on a 45# steel substrate. Under this composition, multiple mechanisms, including high Cr-induced full BCC phase transformation, lattice distortion, and in-situ oxidation self-lubrication, resulted in a coating hardness of 610 HV and an average friction coefficient of only 0.184 without any added reinforcing phases.

[0018] The process of this invention is controllable and low-cost, and it is suitable for wear-resistant protection of mechanical parts. Attached Figure Description

[0019] Figure 1 These are photographs of high-entropy alloy coatings prepared by laser cladding single-pass and double-pass overlapping in Example 1.

[0020] Figure 2 These are photographs of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3.

[0021] Figure 3 The surface hardness of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3 is shown.

[0022] Figure 4 This is a comparison diagram of the longitudinal Vickers hardness variation of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3.

[0023] Figure 5 These are the XRD characterization spectra of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3.

[0024] Figure 6 The graphs show the variation of the friction coefficient of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3 over time.

[0025] Figure 7 This is an EDS surface scan elemental distribution map of the high-entropy alloy coating in Example 1.

[0026] Figure 8This is the EDS energy spectrum and chemical composition table of the high-entropy alloy coating in Example 1.

[0027] Figure 9 These are high-magnification SEM images of the worn surfaces of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3.

[0028] Figure 10 The diagram shows the EBSD phase distribution of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3.

[0029] Figure 11 The images show the grain orientation distribution of the high-entropy alloy coating EBSD prepared in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Example 1: Fe 22.5 Co 22.5 Ni 10 Cr 35 Al 10 Preparation of high-entropy alloy coatings

[0032] (1) Substrate pretreatment: Select No. 45 steel plate with dimensions of 100mm×100mm×10mm as the substrate, sand the surface with sandpaper to remove oxide scale, then ultrasonically clean with acetone and anhydrous ethanol for 15 minutes, and dry with cold air for later use.

[0033] (2) Powder preparation: Weigh metal powders with a purity greater than 99.5% according to the atomic percentages of Fe 22.5 at.%, Co 22.5 at.%, Ni 10 at.%, Cr 35 at.%, and Al 10 at.%, with a particle size of 50-150 μm. Mix the weighed metal powders in a ball mill with a ball-to-powder ratio of 10:1 and a rotation speed of 200 rpm for 4 hours to ensure thorough and uniform mixing, thus obtaining alloy powder.

[0034] (3) Laser cladding: The alloy powder mixed in step 2 is clad onto the surface of the 45# steel substrate after pretreatment in step 1. The coating is formed by synchronous powder feeding and laser cladding, using a multi-layer overlapping method. The process parameters for laser cladding are: laser power 900W, scanning speed 6mm / s, spot diameter 3mm, powder feeding speed 20g / min, protective gas is argon, gas flow rate is 15L / min, overlap rate is controlled at 40%, and coating thickness is controlled at 1.0mm. Figure 1 The images show actual photos of the single-pass and double-pass laser cladding coatings in this embodiment.

[0035] (4) Post-treatment: After cladding, the coating is naturally cooled to room temperature to obtain the high-entropy alloy coating with good wear resistance. The coating prepared in Example 1 is named according to its Cr content and labeled as Cr35.

[0036] Comparative Example 1: Fe 22.5 Co 22.5 Ni 35 Cr 10 Al 10 Preparation of high-entropy alloy coatings

[0037] Following the same preparation method as in Example 1, only the alloy powder composition was adjusted to Fe 22.5 at.%, Co 22.5 at.%, Ni 35 at.%, Cr 10 at.%, and Al 10 at.%, and a high-entropy alloy coating was prepared under the same laser cladding process parameters. The coating formed in Comparative Example 1 is represented by Cr10.

[0038] Comparative Example 2: Fe 22.5 Co 22.5 Ni 25 Cr 20 Al 10 Preparation of high-entropy alloy coatings

[0039] Following the same preparation method as in Example 1, only the alloy powder composition was adjusted to Fe 22.5 at.%, Co 22.5 at.%, Ni 25 at.%, Cr 20 at.%, and Al 10 at.%, and a high-entropy alloy coating was prepared under the same laser cladding process parameters. The coating formed in Comparative Example 2 is represented by Cr20.

[0040] Comparative Example 3: Fe 22.5 Co 22.5 Ni 15 Cr 30 Al 10 Preparation of high-entropy alloy coatings

[0041] Following the same preparation method as in Example 1, only the alloy powder composition was adjusted to Fe 22.5 at.%, Co 22.5 at.%, Ni 15 at.%, Cr 30 at.%, and Al 10 at.%, and a high-entropy alloy coating was prepared under the same laser cladding process parameters. The coating formed in Comparative Example 3 is represented by Cr30.

[0042] Figure 2 Photographs of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3 are shown. The microstructure and mechanical properties of the high-entropy alloy coatings prepared in Example 1 and Comparative Examples 1-3 were characterized, and their strengthening and wear resistance mechanisms were revealed by combining analytical methods such as EBSD.

[0043] (1) Microhardness test: The four-component coatings were tested using a Vickers hardness tester with a load of 200g and a holding time of 15s.

[0044] ① Surface hardness: 10 points were tested on each sample. Test results are as follows. Figure 3 As shown, the surface hardness of the coating increases significantly with increasing Cr content. The surface hardness of Comparative Example 1 (Cr10) is 198.90 HV, that of Comparative Example 2 (Cr20) is 203.82 HV, that of Comparative Example 3 (Cr30) is 525.15 HV, and that of Example 1 (Cr35) reaches 612.23 HV.

[0045] ② Longitudinal hardness of the coating section: Test at 0.1 mm intervals along the coating cross-section from top to the substrate, for a total of 10 points. For example... Figure 4 As shown, the hardness distribution of the four coating components is stable within the cladding layer region, gradually decreasing after entering the heat-affected zone, and stabilizing at approximately 180 HV in the substrate region. In Example 1, the hardness remains at 550-610 HV across the entire cladding layer thickness range of 0.05-0.35 mm, significantly higher than the 500-530 HV of Comparative Example 3 and the 200-215 HV and 195-210 HV of Comparative Examples 2 and 1, respectively. Furthermore, Example 1 exhibits the smoothest hardness transition at the interface, without a significant abrupt drop, indicating optimal microstructure uniformity and metallurgical bonding quality.

[0046] (2) Phase structure analysis: X-ray diffraction was used to analyze the phase structure of the four-component coatings, such as... Figure 5 As shown. The results indicate that Comparative Examples 1 and 2 are dominated by the FCC phase; Comparative Examples 3 and Example 1 show obvious BCC phase diffraction peaks, and the phase structure transforms from FCC-dominated to a two-phase FCC+BCC structure, until Example 1 is dominated by the BCC phase. Further combined with... Figure 10 The EBSD phase analysis shown indicates that the FCC phase volume fraction was 100% in Comparative Examples 1 and 2; the BCC phase volume fraction was 92.3% and the FCC phase was 7.7% in Comparative Example 3; and the BCC phase volume fraction was 100% and the FCC phase was 0% in Example 1, indicating a completely BCC structure.

[0047] (3) Wear resistance test: A reciprocating friction and wear test was conducted using Si3N4 ceramic balls as the grinding pair, with a load of 10 N, a friction frequency of 2 Hz, a friction length of 5 mm, and a test time of 30 min. Figure 6As shown, the results indicate that Example 1 has the lowest friction coefficient and the most stable curve, with an average friction coefficient of 0.184. Comparative Examples 1-3 have friction coefficients of 0.173, 0.276, and 0.191, respectively. However, Comparative Examples 1 and 3 are not stable. In summary, the wear resistance of Example 1 is significantly better than that of Comparative Examples 1-3. Figure 9 The SEM images of the worn surfaces shown indicate that the worn surface of Example 1 is smooth with only minor scratches, while the surfaces of Comparative Examples 1-2 have deep furrows and spalling pits.

[0048] (4) Strengthening and Wear Resistance Mechanism Analysis: Combining the above data and Figure 10 , Figure 11 EBSD analysis revealed that the superior performance of the coating of this invention under conditions without added ceramic reinforcement is attributed to the following synergistic mechanism:

[0049] ① BCC phase transformation strengthening: Increasing Cr to 35 at.% transforms the coating from FCC to a full BCC microstructure, see [link to relevant documentation]. Figure 10 The high intrinsic hardness of the BCC phase is the primary factor contributing to increased hardness, and hardness is strongly positively correlated with the volume fraction of the BCC phase.

[0050] ② Grain boundary strengthening: Figure 11 The EBSD grain boundary statistics show that in Comparative Example 1, small-angle grain boundaries accounted for 10.0% and large-angle grain boundaries for 90.0%; in Comparative Example 2, small-angle grain boundaries accounted for 6.56% and large-angle grain boundaries for 93.4%; and in Example 1, small-angle grain boundaries accounted for 15.7% and large-angle grain boundaries for 84.3%. Example 1 had the highest proportion of small-angle grain boundaries (15.7%), indicating that its internal substructures (dislocations, cellular structures) were the most abundant, and its lattice distortion was the greatest, contributing additional strengthening by hindering dislocation movement. It should be noted that the EBSD grain size statistics show that the grain size of Cr30 is 79.28 μm and the grain size of Cr35 is 73.25 μm, which is coarser than that of Cr10 (57.72 μm) and Cr20 (47.14 μm). This indicates that the hardness improvement in this system does not originate from grain refinement, but mainly depends on the BCC phase transformation and grain boundary / substructure strengthening.

[0051] ③ Severe lattice distortion strengthening and solid solution strengthening: The atomic radii of Fe, Co, Ni, Cr, and Al differ greatly (Cr 0.128 nm, Al 0.143 nm, Fe / Co / Ni 0.124-0.125 nm). High Cr content intensifies the local elastic strain field, strongly hindering dislocation movement. The hardness increases by approximately 87 HV from Cr30 to Cr35, exhibiting nonlinear enhancement, exceeding the predictions of the conventional mixing law.

[0052] ④ In-situ oxide film reduces friction and wear: High Cr promotes the in-situ formation of a dense Cr2O3 oxide film on the worn surface, which isolates the wear pair from direct contact with the coating and changes the wear mechanism from severe abrasive wear to mild oxidative wear. Figure 7-9 The presence of the oxide film is confirmed by the smooth friction layer on the worn surface of Cr35, the elemental distribution map of EDS surface scan, and the enrichment of O element in the chemical composition table.

[0053] Compared with existing technologies, this invention does not rely on external ceramic particles or expensive elements such as Mo and V. It achieves a low-cost, high-hardness, and low-wear wear-resistant coating by precisely controlling the Cr content in the main element and utilizing multiple effects such as BCC phase transformation strengthening, grain boundary / substructure strengthening, lattice distortion strengthening, and in-situ oxidation self-lubrication.

[0054] In summary, this invention, through precise control of the chemical composition of the high-entropy alloy coating, optimizing the Cr content to 35 at.%, and combining it with an optimized laser cladding process, successfully prepared a high-entropy alloy coating with excellent wear resistance on a 45# steel substrate. This coating exhibits high hardness, dense structure, and good adhesion to the substrate, showing broad application prospects in the field of wear-resistant protection.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy alloy wear-resistant coating with BCC phase transformation strengthening and self-lubricating properties, characterized in that, Includes the following steps: Step 1: Substrate pretreatment: Clean and polish the surface of the substrate to remove oil, rust and oxide scale, and clean it with anhydrous ethanol. Dry it for later use. Step 2: Powder preparation: Weigh the metal powder according to the atomic percentages of Fe 22.5 at.%, Co 22.5 at.%, Ni 10 at.%, Cr 35 at.%, and Al 10 at.%, mix them evenly to obtain alloy powder; Step 3: Laser cladding: Using synchronous powder feeding laser cladding technology, the alloy powder mixed in Step 2 is clad onto the surface of the substrate after the pretreatment in Step 1 to form a coating. Step 4: Post-processing: After the cladding is completed, the coating is allowed to cool naturally to room temperature to obtain the high-entropy alloy wear-resistant coating.

2. The preparation method according to claim 2, characterized in that, The purity of the metal powder in step two is greater than 99.5%, and the particle size is 50-150 μm.

3. The preparation method according to claim 2, characterized in that, The laser cladding process parameters in step three are as follows: laser power 900W, scanning speed 6mm / s, spot diameter 3mm, powder feeding speed 20g / min, protective gas is argon, and gas flow rate is 15L / min.

4. The preparation method according to any one of claims 1-3, characterized in that, The coating thickness formed in step three is 1.0 mm.

5. The preparation method according to claim 2, characterized in that, The base material in step one is No. 45 steel.

6. The high-entropy alloy wear-resistant coating prepared by the preparation method according to any one of claims 1-5, characterized in that, The coating is composed of the following atomic percentages of metallic elements: Fe 22.5%, Co 22.5%, Ni 10%, Cr 35%, Al 10%, and the crystal structure of the coating is BCC phase.

7. The high-entropy alloy wear-resistant coating according to claim 6, characterized in that, The surface hardness of the coating is not less than 610 HV, and the average coefficient of friction is 0.184.

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