A self-lubricating high-entropy alloy-based composite material, its preparation method and application

Abstract

This invention relates to the field of lubrication materials technology, and more particularly to a self-lubricating high-entropy alloy-based composite material, its preparation method, and its application. The invention provides a method for preparing a self-lubricating high-entropy alloy-based composite material, comprising the following steps: mixing Al, Co, Fe, Ni, Ti, and B, followed by vacuum arc melting to obtain a high-entropy alloy bulk; performing pore-forming corrosion on the high-entropy alloy bulk using an etching solution to obtain a porous high-entropy alloy; mixing sodium molybdate, thiourea, and water to obtain a precursor solution; and placing the porous high-entropy alloy in the precursor solution for sequential vacuum impregnation and hydrothermal reaction to obtain the self-lubricating high-entropy alloy-based composite material. The self-lubricating high-entropy alloy-based composite material prepared by this method possesses both excellent mechanical properties and low friction and low wear characteristics.

Description

Technical Field

[0001] This invention relates to the field of lubrication materials technology, and in particular to a self-lubricating high-entropy alloy-based composite material, its preparation method, and its application. Background Technology

[0002] High-entropy alloys are a class of novel metallic materials with simple face-centered cubic, body-centered cubic, or hexagonal close-packed structures, composed of various metallic or non-metallic elements. The unique high-entropy effect, hysteretic diffusion effect, lattice distortion effect, and cocktail effect of high-entropy alloys endow them with performance advantages unmatched by conventional metallic materials, such as high strength, high hardness, good high-temperature structural stability, resistance to high-temperature softening, and excellent wear resistance and corrosion resistance. Furthermore, the similar content of the principal elements in high-entropy alloys shifts the selection of alloy types from the peripheral regions of the phase diagram to the central regions, greatly expanding the selection space for high-entropy alloys. This allows for the optimization of the composition of high-entropy alloys through specific element selection to achieve specified properties and meet the application requirements of high-entropy alloys under special working conditions. Therefore, high-entropy alloys have broad application prospects in cutting-edge technology fields such as aerospace, marine equipment, defense, and rail transportation.

[0003] Currently, the high coefficient of friction of high-entropy alloys is the main bottleneck limiting their use as high-end lubricating and wear-resistant materials. Researchers typically mix self-lubricating materials such as graphite, Ag, BN, CaF2, and BaF2 with high-entropy alloy powders, using a combination of ball milling and hot-pressing sintering to prepare high-entropy alloy-based self-lubricating composites to reduce the coefficient of friction. However, due to the low strength and hardness of the lubricant and the poor interfacial wettability between the lubricant and the high-entropy alloy, the mechanical and wear-resistant properties of these self-lubricating composites prepared by conventional methods are significantly reduced. Furthermore, the high surface energy of nanoscale lubricants makes them prone to agglomeration during ball milling, leading to inconsistent overall performance of self-lubricating composites prepared by conventional methods. Therefore, there is a need to propose new design methods for self-lubricating high-entropy alloy-based composites and develop novel self-lubricating high-entropy alloy-based composites that combine good mechanical properties with low friction and low wear. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a self-lubricating high-entropy alloy-based composite material, its preparation method, and its application. The self-lubricating high-entropy alloy-based composite material prepared by the method possesses both excellent mechanical properties and low friction and low wear characteristics.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] This invention provides a method for preparing a self-lubricating high-entropy alloy-based composite material, comprising the following steps:

[0007] Al, Co, Fe, Ni, Ti and B are mixed and then vacuum arc melted to obtain a high-entropy alloy bulk.

[0008] The high-entropy alloy block was subjected to pore-forming corrosion using an etchant to obtain a porous high-entropy alloy.

[0009] Sodium molybdate, thiourea, and water were mixed to obtain a precursor solution;

[0010] The porous high-entropy alloy was placed in the precursor solution and subjected to vacuum impregnation and hydrothermal reaction in sequence to obtain the self-lubricating high-entropy alloy-based composite material.

[0011] Preferably, the atomic ratio of Al, Co, Fe, Ni, Ti and B is (1.0-8.0):(10-40):(9-29):(10-40):(2.0-14):(7.0-28).

[0012] Preferably, the vacuum arc melting temperature is ≥2100℃, the vacuum degree is ≤-0.06MPa, the time is ≥1.5min, and the number of times is ≥3.

[0013] Preferably, the corrosive liquid comprises hydrochloric acid, glycerol, and nitric acid in a volume ratio of (10-22):(6-16):(0.6-5);

[0014] The hydrochloric acid has a mass concentration of 36.0% to 38.0%, and the nitric acid has a mass concentration of 65.0% to 68.0%.

[0015] Preferably, the mass ratio of sodium molybdate, thiourea, and water is (0.1–0.4):(0.4–1.0):(40–110).

[0016] Preferably, before performing the pore-forming corrosion, the porous high-entropy alloy is further polished;

[0017] The surface roughness of the porous high-entropy alloy obtained after polishing is ≤0.5μm.

[0018] Preferably, the vacuum degree of the vacuum impregnation is -0.08 to -0.03 MPa, and the time is 0.5 to 1.5 h.

[0019] Preferably, the hydrothermal reaction is carried out at a temperature of 160–230°C for a duration of ≥20 h.

[0020] The present invention also provides a self-lubricating high-entropy alloy matrix composite material prepared by the preparation method described above, comprising a porous high-entropy alloy matrix and MoS2 particles in situ distributed on the surface and in the pores of the porous high-entropy alloy matrix.

[0021] The present invention also provides the application of the self-lubricating high-entropy alloy-based composite material described above in the field of lubrication.

[0022] This invention provides a method for preparing a self-lubricating high-entropy alloy-based composite material, comprising the following steps: mixing Al, Co, Fe, Ni, Ti, and B, followed by vacuum arc melting to obtain a high-entropy alloy bulk; performing pore-forming corrosion on the high-entropy alloy bulk using an etching solution to obtain a porous high-entropy alloy; mixing sodium molybdate, thiourea, and water to obtain a precursor solution; and placing the porous high-entropy alloy in the precursor solution for sequential vacuum impregnation and hydrothermal reaction to obtain the self-lubricating high-entropy alloy-based composite material. This invention prepares a high-entropy alloy with a porous micro / nano structure on its surface using a combination of vacuum arc melting and chemical corrosion. Then, vacuum impregnation technology is used to fill the surface of the high-entropy alloy and its micro / nano pores with the precursor solution. Through hydrothermal reaction, in-situ MoS2 is formed within the micro / nano pores of the high-entropy alloy surface, resulting in uniform and substantial MoS2 particles loading the surface of the high-entropy alloy and its micro / nano pores. Compared with high-entropy alloy-based composite materials prepared by directly mixing high-entropy alloy powder and MoS2 powder using conventional methods, the self-lubricating high-entropy alloy composite material of the present invention greatly reduces the wear rate and friction coefficient while maintaining its original mechanical properties, and has broad application prospects in the field of lubrication materials technology. Attached Figure Description

[0023] Figure 1 Al3Co obtained by vacuum arc melting in Example 1 28 Fe 14 Ni 28 Ti7B 20 XRD pattern of high-entropy alloy bulk material;

[0024] Figure 2 This is a SEM image of the porous high-entropy alloy with micro-nano pores on the surface obtained after chemical etching in Example 1.

[0025] Figure 3 The morphology and composition of the in-situ MoS2 formed by the hydrothermal reaction in Example 1 are shown.

[0026] Figure 4 The images shown are SEM, EDS, and XRD patterns of the self-lubricating high-entropy alloy-based composite material described in Example 1.

[0027] Figure 5 The composition of the high-entropy alloy block prepared by arc melting in Example 2;

[0028] Figure 6 This is a SEM image of the porous high-entropy alloy with micro-nano pores on the surface obtained after chemical etching in Example 2.

[0029] Figure 7 The morphology and composition of the in-situ MoS2 formed by the hydrothermal reaction in Example 2 are shown.

[0030] Figure 8 The images shown are SEM and EDS images of the self-lubricating high-entropy alloy-based composite material described in Example 2.

[0031] Figure 9 The friction coefficient-time curve of the self-lubricating high-entropy alloy-based composite material described in Example 1;

[0032] Figure 10 The friction coefficient-time curve of the self-lubricating high-entropy alloy-based composite material described in Example 2;

[0033] Figure 11 The friction coefficient-time curve is shown for the porous high-entropy alloy described in Comparative Example 1. Detailed Implementation

[0034] This invention provides a method for preparing a self-lubricating high-entropy alloy-based composite material, comprising the following steps:

[0035] Al, Co, Fe, Ni, Ti and B are mixed and then vacuum arc melted to obtain a high-entropy alloy bulk.

[0036] The high-entropy alloy block was subjected to pore-forming corrosion using an etchant to obtain a porous high-entropy alloy.

[0037] Sodium molybdate, thiourea, and water were mixed to obtain a precursor solution;

[0038] The porous high-entropy alloy was placed in the precursor solution and subjected to vacuum impregnation and hydrothermal reaction in sequence to obtain the self-lubricating high-entropy alloy-based composite material.

[0039] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0040] This invention involves mixing Al, Co, Fe, Ni, Ti, and B, followed by vacuum arc melting to obtain a high-entropy alloy bulk.

[0041] In this invention, Al, Co, Fe, Ni, Ti and B are preferably elemental particles; Al, Co, Fe, Ni and Ti are preferably columnar particles with a size of φ(3~10)×(5~10)mm, more preferably columnar particles with a size of φ(3~5)×5mm; B is preferably irregular particles with a size ≤5mm, more preferably irregular particles with a size ≤3mm.

[0042] In this invention, the atomic ratio of Al, Co, Fe, Ni, Ti and B is preferably (1.0-8.0):(10-40):(9-29):(10-40):(2.0-14):(7.0-28), more preferably (2.0-7.0):(15-35):(11-27):(15-35):(4.0-12.0):(10-25), and most preferably (3.0-6.0):(20-30):(13-25):(20-30):(6.0-10):(13-22).

[0043] In this invention, the vacuum arc melting temperature is preferably ≥2100℃, more preferably ≥2250℃, and most preferably 2400~2500℃; the vacuum degree is preferably ≤-0.06MPa, more preferably ≤-0.05MPa, and most preferably -0.04~-0.045MPa; the melting time is preferably ≥1.5min, more preferably ≥3.0min, and most preferably 3.5~5.0min; the number of melting cycles is preferably ≥3 times, more preferably ≥5 times, and most preferably 7~9 times. In this invention, the crucible used for vacuum arc melting is preferably a water-cooled copper crucible. In this invention, the control of the above-mentioned arc melting parameters can obtain a dense and uniform high-entropy alloy block without metallurgical defects such as shrinkage porosity, which facilitates the subsequent construction of micro-nano pores on the surface of the high-entropy alloy by chemical etching.

[0044] After obtaining the high-entropy alloy block, the present invention uses an etching solution to perform pore-forming etching on the high-entropy alloy block to obtain a porous high-entropy alloy.

[0045] In this invention, before performing the pore-forming etching, it is preferable to polish the porous high-entropy alloy; the surface roughness (Sa) of the porous high-entropy alloy obtained after polishing is preferably ≤0.5μm, more preferably ≤0.4μm, and most preferably 0.1~0.3μm. In this invention, the polishing process is preferably performed by sequentially grinding the high-entropy alloy with 80-mesh, 240-mesh, 400-mesh, 600-mesh, 800-mesh, 1000-mesh, 1500-mesh, and 2000-mesh SiC abrasive paper, followed by polishing the high-entropy alloy with a particle size of less than 0.5μm.

[0046] In this invention, the polishing can reduce the roughness of the high-entropy alloy surface, which helps to construct uniformly distributed micro-nano pores on the high-entropy alloy surface through chemical etching, and is also beneficial to the in-situ formation and uniform adhesion of MoS2 particles.

[0047] In this invention, the etching solution preferably comprises hydrochloric acid, glycerol, and nitric acid in a volume ratio of (10–22):(6–16):(0.6–5), more preferably (12–20):(8–14):(0.8–4), and most preferably (14–18):(10–12):(1–3). In this invention, the mass concentration of the hydrochloric acid is preferably 36.0%–38.0%, and the mass concentration of the nitric acid is preferably 65.0%–68.0%. In this invention, the etching solution is preferably prepared by mixing hydrochloric acid, glycerol, and nitric acid.

[0048] In this invention, the preferred method of pore-forming corrosion is to coat any polished surface of the high-entropy alloy block with the corrosion solution or to immerse any polished surface of the high-entropy alloy block in the corrosion solution.

[0049] In this invention, the temperature of the pore-forming corrosion is preferably room temperature; the time is preferably 2.0 to 5.0 min, more preferably 2.5 to 4.0 min, and most preferably 3.0 to 3.5 min.

[0050] After the pore-forming etching is completed, the present invention preferably includes cleaning, which is preferably performed by washing with acetone and deionized water in sequence; the present invention does not have any special limitation on the washing method, and any method known to those skilled in the art can be used.

[0051] In this invention, the pore size of the porous high-entropy alloy is preferably 50-450 μm, more preferably 100-400 μm, and most preferably 150-360 μm.

[0052] The preparation method of the present invention further includes mixing sodium molybdate, thiourea and water to obtain a precursor solution.

[0053] In this invention, the water is preferably deionized water. The mass ratio of sodium molybdate, thiourea, and water is preferably (0.1–0.4):(0.4–1.0):(40–110), more preferably (0.15–0.35):(0.5–0.9):(55–95), and most preferably (0.2–0.3):(0.6–0.8):(70–80). In this invention, the water is preferably deionized water.

[0054] In this invention, the mixing is preferably carried out by adding sodium molybdate and thiourea sequentially to water.

[0055] In this invention, the mixing is preferably carried out under stirring conditions. This invention does not impose any special limitations on the stirring conditions; conditions well known to those skilled in the art can be used to ensure that the sodium molybdate and thiourea are fully dissolved in the water.

[0056] In this invention, the mixing temperature is preferably room temperature; the mixing time is preferably ≥5.0h, more preferably ≥10.0h, and most preferably 20-24h.

[0057] After obtaining the porous high-entropy alloy and the precursor solution, the present invention places the porous high-entropy alloy in the precursor solution and performs vacuum impregnation and hydrothermal reaction in sequence to obtain the self-lubricating high-entropy alloy-based composite material.

[0058] The present invention does not impose any special limitation on the amount of the precursor solution used; any amount known to those skilled in the art can be used, provided that the porous high-entropy alloy is completely submerged.

[0059] In this invention, the porous high-entropy alloy has its micro-nano pores facing upwards to facilitate the full immersion of the precursor solution.

[0060] In this invention, the vacuum degree of the vacuum impregnation is preferably -0.08 to -0.03 MPa, more preferably -0.07 to -0.04 MPa, and most preferably -0.06 to -0.05 MPa; the time is preferably 0.5 to 1.5 h, more preferably 0.8 to 1.3 h, and most preferably 1.0 to 1.2 h.

[0061] After the vacuum impregnation is completed, the present invention preferably transfers the vacuum-impregnated porous high-entropy alloy into a polytetrafluoroethylene liner while keeping the side of the porous high-entropy alloy with micro-nano pores facing upwards.

[0062] In this invention, in order to make the reaction more complete, it is preferable to add a new precursor solution to the polytetrafluoroethylene liner containing the vacuum-impregnated porous high-entropy alloy, and to completely immerse the vacuum-impregnated porous high-entropy alloy in the precursor solution.

[0063] In this invention, the temperature of the hydrothermal reaction is preferably 160-230°C, more preferably 170-220°C, and most preferably 180-210°C; the time is preferably ≥20h, more preferably ≥22h, and most preferably 23-24h.

[0064] In this invention, during the hydrothermal reaction, sodium molybdate and thiourea generate MoS2 micro / nano particles in situ; the conditions of the hydrothermal reaction allow MoS2 to react fully and deposit in situ within the pores of the porous high-entropy alloy.

[0065] After the hydrothermal reaction is completed, the present invention preferably includes sequential cooling, solid-liquid separation, and drying. In the present invention, the cooling is preferably furnace-based cooling. In the present invention, the drying is preferably vacuum drying, the vacuum drying temperature is preferably 80–100°C, more preferably 85–95°C, and most preferably 88–92°C; the time is preferably 5–12 hours, more preferably 6–12 hours.

[0066] The present invention also provides a self-lubricating high-entropy alloy matrix composite material prepared by the preparation method described above, comprising a porous high-entropy alloy matrix and MoS2 particles in situ distributed on the surface and in the pores of the porous high-entropy alloy matrix.

[0067] In this invention, the particle size of the MoS2 particles is preferably 0.9 to 2.6 μm, and the average particle size is preferably 1.3 μm.

[0068] This invention also provides the application of the self-lubricating high-entropy alloy-based composite material described above in the field of lubrication. This invention does not impose any special limitations on the method of application; any method well-known to those skilled in the art can be used.

[0069] The following detailed description, in conjunction with embodiments, illustrates the self-lubricating high-entropy alloy-based composite material, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0070] Example 1

[0071] Weigh 100g of mixed raw material particles (Al, Co, Fe, Ni, Ti, and B elemental particles) according to the ratio Al:Co:Fe:Ni:Ti:B = 3:28:14:28:7:20, based on atomic percentage. The particle size of the Al, Co, Fe, Ni, and Ti elemental particles is [missing information]. The average particle size of B is ≤3mm. The resulting mixture is pre-placed in a water-cooled copper crucible and subjected to vacuum arc melting to obtain Al3Co. 28 Fe 14 Ni 28 Ti7B 20 The high-entropy alloy block was melted by electric arc at a temperature of 2500℃, a vacuum of -0.045MPa, a melting time of 5.0min, and 9 melting cycles. Afterward, it was cooled to room temperature in the furnace to obtain a dense and uniform high-entropy alloy block without metallurgical defects such as shrinkage porosity.

[0072] The high-entropy alloy block was polished sequentially using SiC sandpaper with grits of 80 mesh, 240 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1500 mesh and 2000 mesh, and then further polished with water-soluble diamond polishing paste with a particle size of 0.5 μm to obtain a high-entropy alloy block with a surface roughness Sa = 0.1 μm;

[0073] Hydrochloric acid, glycerol and nitric acid were mixed in a volume ratio of 6:2:1 to obtain 33 mL of etching solution. One of the polished surfaces of the high-entropy alloy was coated with the prepared etching solution and etched for 3 min. After being removed, it was washed with acetone and deionized water in sequence and then dried in an oven at 85 °C for 2 h to obtain a high-entropy alloy block with micro-nano pores on the surface after drying.

[0074] 0.2g sodium molybdate and 0.6g thiourea granules were added sequentially to 70g deionized water and stirred electromagnetically for 20h at room temperature to obtain a precursor solution.

[0075] A dried high-entropy alloy block with micro- and nano-pores on its surface was completely immersed in a precursor solution, with the porous side facing upwards. Vacuum impregnation was performed at -0.06 MPa for 1.0 h to ensure the precursor solution completely penetrated the micro- and nano-pores on the high-entropy alloy surface. The vacuum-impregnated high-entropy alloy was then transferred to a polytetrafluoroethylene (PTFE) liner, with the porous side facing upwards. A freshly prepared precursor solution was added to the PTFE liner, completely immersing the high-entropy alloy block. The PTFE liner was then placed in a stainless steel high-pressure reactor, which was placed in an oven at 180°C for 24 h of hydrothermal reaction, followed by furnace cooling to room temperature. The porous high-entropy alloy with deposited MoS2 was removed and dried in a vacuum oven at 100°C for 5.0 h to obtain a self-lubricating high-entropy alloy-based composite material.

[0076] The composition and microstructure of arc-melted high-entropy alloy bulk, porous high-entropy alloy with micro / nano pores on the surface, in-situ MoS2 particles formed by hydrothermal reaction, and self-lubricating high-entropy alloy matrix composites were analyzed using XRD and SEM. The results are as follows: Figures 1 to 4 As shown, Figure 1 To obtain Al3Co through vacuum arc melting 28 Fe 14 Ni 28 Ti7B 20 XRD patterns of high-entropy alloy blocks, by Figure 1 It can be seen that the high-entropy alloy is composed of a corrosion-resistant continuous titanium-rich FCC1 matrix phase, an in-situ precipitated TiB2 phase, and a non-corrosion-resistant micro-nano titanium-poor FCC2 in-situ precipitated phase. Figure 2This is a SEM image of a porous high-entropy alloy with micro- and nano-pores on its surface, obtained after chemical etching. Figure 2 It can be seen that after chemical corrosion, the in-situ precipitated phase of the non-corrosion-resistant titanium-poor FCC2 is dissolved by corrosion, forming micro-nano pores with a diameter of about 200-360 nm on the surface of the high-entropy alloy. Figure 3 The images show the morphology and composition of in-situ MoS2 formed by hydrothermal reaction. (a) shows the morphology of in-situ MoS2 formed by hydrothermal reaction, (b) shows the EDS spectrum of in-situ MoS2 formed by hydrothermal reaction, and (c) shows the XRD spectrum of in-situ MoS2 formed by hydrothermal reaction. As shown in (a), spherical particles with diameters of 1.0–2.5 μm were formed after hydrothermal reaction. The EDS and XRD analysis results in (b) and (c) show that the atomic ratio of Mo to S in these spherical particles is 1:2, indicating that in-situ MoS2 particles were indeed formed after hydrothermal reaction. Figure 4 Images (a), (b), and (c) in the figure are SEM, EDS, and XRD patterns of the self-lubricating high-entropy alloy-based composite material, respectively. Figure 4 It can be seen that, through hydrothermal reaction, a dense MoS2 layer is formed on the surface of the high-entropy alloy and inside the micro-nano pores on the surface, and the original phase composition of the high-entropy alloy remains unchanged.

[0077] Example 2

[0078] Weigh 150g of raw material particles (Al, Co, Fe, Ni, Ti, and B elemental particles) according to the ratio Al:Co:Fe:Ni:Ti:B = 6:25:25:25:6:13, based on atomic percentage. The particle size of the Al, Co, Fe, Ni, and Ti elemental particles is [missing information]. The average particle size of B is ≤2mm. The resulting mixture was pre-placed in a water-cooled copper crucible for vacuum arc melting at a temperature of 2400℃, a vacuum of -0.04MPa, a melting time of 3.5min, and 7 melting cycles. Afterward, the mixture was cooled to room temperature in the furnace to obtain Al6Co. 25 Fe 25 Ni 25 Ti6B 13 High-entropy alloy bulk;

[0079] The high-entropy alloy was polished sequentially using SiC sandpaper of 240 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1500 mesh, and 2000 mesh, and water-soluble diamond polishing paste with a particle size of 0.25 μm, to obtain a high-entropy alloy block with a surface roughness Sa = 0.3 μm.

[0080] Hydrochloric acid, glycerol and nitric acid were mixed in a volume ratio of 14:10:1 to obtain 25.0 mL of etching solution. The mixed etching solution was coated on the polished surface of the high entropy alloy and etched for 3.5 min. After washing with acetone and deionized water, it was dried in an oven at 100 °C for 1.5 h to obtain a dried high entropy alloy block with micro-nano pores on the surface.

[0081] 0.3g sodium molybdate and 0.8g thiourea granules were added sequentially to 80g deionized water and stirred electromagnetically for 24h to obtain a precursor solution.

[0082] A dried high-entropy alloy block with micro- and nano-pores on its surface was completely immersed in a precursor solution, with the porous side facing vertically upwards. Vacuum impregnation was performed at -0.05 MPa for 1.2 hours to ensure complete penetration of the precursor solution into the micro- and nano-pores. The vacuum-impregnated high-entropy alloy was then transferred to a polytetrafluoroethylene (PTFE) liner, with the porous side facing upwards. A freshly prepared precursor solution was added to the PTFE liner, completely immersing the high-entropy alloy block. The PTFE liner was then placed in a stainless steel high-pressure reactor, which was subjected to a hydrothermal reaction at 210°C for 23 hours, followed by furnace cooling to room temperature. The surface-porous high-entropy alloy with deposited MoS2 was removed and dried in a vacuum oven at 80°C for 12 hours to obtain a self-lubricating high-entropy alloy-based composite material.

[0083] The composition and microstructure of high-entropy alloy bulk, porous high-entropy alloy with micro / nano pores on the surface, in-situ MoS2 particles formed by hydrothermal reaction, and self-lubricating high-entropy alloy matrix composites were analyzed using XRD and SEM. The results are as follows: Figures 5 to 8 As shown, Figure 5 The composition of the high-entropy alloy bulk prepared by arc melting, which consists of corrosion-resistant FCC1 and TiB2 phases and a non-corrosion-resistant Ti-depleted phase FCC2; Figure 6 The image shows a porous high-entropy alloy with micro-nano pores on the surface obtained after chemical etching. The in-situ precipitated phase of the non-corrosion-resistant titanium-poor FCC2 was dissolved by corrosion, forming micro-nano pores with a diameter of 150-250 nm on the surface of the high-entropy alloy. Figure 7 The morphology and composition of in-situ MoS2 formed by hydrothermal reaction are described by... Figure 7 It can be seen that spherical particles with diameters of 0.9 to 2.0 μm were formed after the hydrothermal reaction. The EDS analysis results show that the atomic ratio of Mo to S in these spherical particles is close to 1:2, indicating that in-situ MoS2 particles were indeed formed after the hydrothermal reaction. Figure 8 In the image, (a) and (b) are the SEM and EDS images of the self-lubricating high-entropy alloy-based composite material, respectively. Figure 8It can be seen that, through hydrothermal reaction, a dense MoS2 layer is formed on the surface of the high-entropy alloy and inside the micro-nano pores on the surface, and the original phase composition of the high-entropy alloy remains unchanged.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that the high-entropy alloy surface and its micro-nano pores are not loaded with MoS2 formed through hydrothermal reaction. The specific implementation steps are as follows:

[0086] Al, Co, Fe, Ni, and Ti particles with a size of φ3×5mm and B particles with an average particle size ≤3mm were used as raw materials. 100g of raw material particles were weighed according to the atomic percentage ratio of Al:Co:Fe:Ni:Ti:B = 3:28:14:28:7:20. The mixed raw materials were pre-placed in a water-cooled copper crucible for vacuum arc melting to obtain Al3Co. 28 Fe 14 Ni 28 Ti7B 20 High-entropy alloy blocks were arc-melted at a temperature of 2500℃, a vacuum of -0.045MPa, a melting time of 5.0min, and 9 melting cycles. Afterward, the blocks were cooled to room temperature in the furnace, resulting in dense, uniform high-entropy alloy blocks free from metallurgical defects such as shrinkage porosity. The arc-melted high-entropy alloy blocks were then polished sequentially with SiC sandpaper of 80, 240, 400, 600, 800, 1000, 1500, and 2000 mesh. Further polishing with a 0.5μm water-soluble diamond polishing paste yielded a high-entropy alloy block with a surface roughness Sa = 0.1μm.

[0087] Hydrochloric acid, glycerol, and nitric acid were mixed in a ratio of 6:2:1 to obtain 33 mL of etching solution. One of the polished surfaces of the high-entropy alloy was coated with the prepared etching solution and etched for 3 min. After being removed, the alloy was washed with acetone and deionized water in sequence and then dried in an oven at 85 °C for 2 h to obtain a high-entropy alloy block with micro-nano pores on its surface.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the temperature for the hydrothermal reaction is set at 140°C.

[0090] 100g of mixed raw material particles were weighed according to the atomic percentage ratio of Al:Co:Fe:Ni:Ti:B = 3:28:14:28:7:20, where Al, Co, Fe, Ni, and Ti were particles with a diameter of φ3×5mm, and B was particles with an average particle size ≤3mm. The mixed raw material was pre-placed in a water-cooled copper crucible and subjected to vacuum arc melting to obtain Al3Co. 28 Fe14 Ni 28 Ti7B 20 High-entropy alloy blocks were arc-melted at a temperature of 2500℃, a vacuum of -0.045MPa, a melting time of 5.0min, and 9 melting cycles. Afterward, the blocks were cooled to room temperature in the furnace, resulting in dense, uniform high-entropy alloy blocks free from metallurgical defects such as shrinkage porosity. The arc-melted high-entropy alloy blocks were then polished sequentially with SiC sandpaper of 80, 240, 400, 600, 800, 1000, 1500, and 2000 mesh. Further polishing with a 0.5μm water-soluble diamond polishing paste yielded a high-entropy alloy block with a surface roughness Sa = 0.1μm.

[0091] Hydrochloric acid, glycerol and nitric acid were mixed in a volume ratio of 6:2:1 to obtain 33 mL of etching solution. One of the polished surfaces of the high-entropy alloy was coated with the prepared etching solution and etched for 3 min. After that, it was taken out and washed with acetone and deionized water in sequence. It was then dried in an oven at 85 °C for 2 h to obtain a high-entropy alloy block with micro-nano pores on the surface.

[0092] 0.2g sodium molybdate and 0.6g thiourea granules were added sequentially to 70g deionized water and stirred electromagnetically for 20h at room temperature to obtain a precursor solution.

[0093] A dried high-entropy alloy block with micro- and nano-pores on its surface was completely immersed in a precursor solution, with the porous side facing vertically upwards. Vacuum impregnation was performed at -0.06 MPa for 1.0 h to ensure the precursor solution completely penetrated the micro- and nano-pores on the high-entropy alloy surface. The vacuum-impregnated high-entropy alloy was then transferred to a polytetrafluoroethylene (PTFE) liner, with the porous side facing upwards. A freshly prepared precursor solution was added to the PTFE liner, completely immersing the high-entropy alloy block. The PTFE liner was then placed in a stainless steel high-pressure reactor, which was placed in an oven at 140°C for 24 h of hydrothermal reaction, followed by furnace cooling to room temperature. The porous high-entropy alloy with deposited MoS2 was removed and dried in a vacuum oven at 100°C for 5.0 h to obtain a self-lubricating high-entropy alloy-based composite material.

[0094] Test Case

[0095] The hardness of the high-entropy alloy and the self-lubricating high-entropy alloy-based composite material was tested using an HV-5 Vickers hardness tester with a load of 300g and a holding time of 15s. The coefficient of friction and wear rate of the high-entropy alloy and the self-lubricating high-entropy alloy-based composite material at 25℃, 150℃, and 300℃ were tested using an HT-1000 high-temperature friction molding tester with a friction load of 10N, a rotation speed of 360r / min, a rotation radius of 5mm, and a friction time of 45min. A 6.0mm diameter Si3N4 ball was used as the mating material. The test results for hardness, coefficient of friction, and wear rate of the examples and comparative examples are shown in Table 1. Figure 9 , Figure 10 and Figure 11 The friction coefficient-time curves are those of the self-lubricating high-entropy alloy-based composite material described in Example 1, the self-lubricating high-entropy alloy-based composite material described in Example 2, and the surface porous high-entropy alloy described in Comparative Example 1.

[0096] Table 1. Hardness, coefficient of friction, and wear rate at 25°C, 150°C, and 300°C for high-entropy alloys (Comparative Examples 1-2) and self-lubricating high-entropy alloy-based composites (Examples 1-2).

[0097]

[0098] The experimental results from the above examples and comparative examples show that, within the temperature range of 25–300℃, the porous high-entropy alloy matrix exhibits a high coefficient of friction and wear rate, with a large fluctuation range and poor stability in the coefficient of friction. However, the self-lubricating high-entropy alloy matrix composite material with surface-loaded in-situ MoS2, prepared by a combination of arc melting, chemical corrosion, and hydrothermal reaction, can significantly reduce the coefficient of friction and wear rate of the high-entropy alloy while maintaining essentially unchanged mechanical properties, reducing the fluctuation range of the coefficient of friction, and improving the stability of the coefficient of friction. Further analysis reveals that the precursor solution concentration in Example 2 is higher than that in Example 1, resulting in the formation of more MoS2 in the pores and on the surface of the high-entropy alloy in Example 2, thus giving it a lower and more stable coefficient of friction and wear rate. In Comparative Example 2, due to the lower hydrothermal reaction temperature, insufficient MoS2 was formed, leading to a significant increase in both the coefficient of friction and wear rate. This demonstrates that the preparation method and designed reaction conditions of the novel self-lubricating high-entropy alloy-based composite material provided by this invention are both reasonable and feasible, and the self-lubricating high-entropy alloy-based composite material prepared by this method has extremely high application potential in the field of self-lubrication.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 self-lubricating high-entropy alloy-based composite material, characterized in that, Includes the following steps: Al, Co, Fe, Ni, Ti and B are mixed and then vacuum arc melted to obtain a high-entropy alloy bulk. The atomic ratio of Al, Co, Fe, Ni, Ti and B in the high-entropy alloy bulk is (1.0~8.0):(10~40):(9~29):(10~40):(2.0~14):(7.0~28); The high-entropy alloy block was subjected to pore-forming corrosion using an etchant to obtain a porous high-entropy alloy. Sodium molybdate, thiourea, and water were mixed to obtain a precursor solution; The porous high-entropy alloy was placed in the precursor solution and subjected to vacuum impregnation and hydrothermal reaction in sequence to obtain the self-lubricating high-entropy alloy-based composite material. The vacuum arc melting temperature is ≥2100℃, the vacuum degree is ≤-0.06MPa, the time is ≥1.5min, and the number of times is ≥3. The corrosive solution comprises hydrochloric acid, glycerol, and nitric acid in a volume ratio of (10~22):(6~16):(0.6~5); The hydrochloric acid has a mass concentration of 36.0% to 38.0%, and the nitric acid has a mass concentration of 65.0% to 68.0%. The temperature of the hydrothermal reaction is 160~230℃.

2. The preparation method according to claim 1, characterized in that, The mass ratio of sodium molybdate, thiourea, and water is (0.1~0.4):(0.4~1.0):(40~110).

3. The preparation method according to claim 1, characterized in that, Before performing the pore-forming corrosion, the high-entropy alloy block is also polished. The surface roughness of the high-entropy alloy block obtained after polishing is ≤0.5μm.

4. The preparation method according to claim 1, characterized in that, The vacuum impregnation process involves a vacuum level of -0.08 to -0.03 MPa and a duration of 0.5 to 1.5 hours.

5. The preparation method according to claim 1, characterized in that, The hydrothermal reaction time is ≥20h.

6. The self-lubricating high-entropy alloy-based composite material prepared by the preparation method according to any one of claims 1 to 5, characterized in that, It includes a porous high-entropy alloy matrix and MoS2 particles distributed in situ on the surface and within the pores of the porous high-entropy alloy matrix.

7. The application of the self-lubricating high-entropy alloy-based composite material according to claim 6 in the field of lubrication.

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