Anti-cavitation lubrication wear-resistant high-entropy alloy composite coating and preparation method thereof

Abstract

The application discloses an anti-cavitation lubrication wear-resistant high-entropy alloy composite coating and a preparation method thereof. The application adopts single FCC phase Al-Cr-Co-Ni quaternary high-entropy alloy and Ag mixed powder with (111) crystal face preferred orientation as spraying powder, and prepares the high-entropy alloy composite coating through a thermal spraying technology. The lubricating phase Ag of the composite coating prepared by the application is uniformly distributed in the high-entropy alloy matrix but does not form solid solution, and the crystal structures of the two are effectively reserved, and under the action of external force, the two are easily sheared into films and deformed to absorb energy, so that the composite coating exhibits excellent lubrication and anti-cavitation performance in low-viscosity aviation kerosene. Meanwhile, the inherent lattice distortion effect of the high-entropy alloy and the self-strengthening behavior generated in the spraying process also make the composite coating have good bearing capacity, so the wear resistance is also outstanding. Compared with the commonly used adhesive solid lubrication coating on the surface of the mechanical part of the fuel pump, the comprehensive performance of the coating of the application is obviously better, and the coating is more suitable for use in the working condition environment where cavitation and wear exist simultaneously.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of advanced metal materials and surface protection technology, and particularly relates to an anti-cavitation lubrication wear-resistant high-entropy alloy composite coating and a preparation method thereof. BACKGROUND

[0002] In order to further improve the thrust-to-weight ratio and fuel combustion efficiency of the aero-engine, the rotating speed, load of the engine fuel pump thrust bearing / gear friction pair and the temperature of the oil medium in the fuel pump are continuously increasing, which leads to a decrease in the viscosity of the fuel and a deterioration in the ability to form an oil film on the surface of the component, but the cavitation degree becomes more severe, causing more serious wear and cavitation combined damage to the thrust bearing and gear and other components, seriously affecting the service life and operation stability of the related components and posing a potential threat to the flight safety of the aircraft.

[0003] MoS2-based, graphite-based and other adhesive solid lubricating coatings can significantly improve the tribological performance of thrust bearings and other components in the condition of poor oil film due to their excellent solid lubrication performance, and therefore have been widely studied and used in the United States, Russia and China (CN112251135A). However, with the continuous increase in the rotating speed of the fuel pump and the temperature of the oil, the protective effect of such coatings is significantly deteriorated, and large-scale peeling caused by cavitation often occurs, thereby affecting the friction-reducing and wear-resistant effect. The reason is that the adhesive solid lubricating coating usually uses organic resin as the binder, which has poor mechanical strength and temperature resistance, and is difficult to resist the high-frequency impact and high-temperature burning caused by the collapse of tens of thousands of bubbles formed by oil cavitation, and is prone to cracking, melting and carbonization (China Surface Engineering, 2024, 37(5), 1-14); in addition, MoS2 and graphite are inorganic materials, which have large differences in properties with organic resin, the interface bonding between them is poor, and the deformation response under external force is obviously different, so interface cracking and peeling are also prone to occur. The existence of these problems greatly limits the improvement of the performance of the fuel pump, and a new type of surface coating that takes into account the anti-cavitation and lubrication wear-resistant functions is urgently needed.

[0004] The invention patent with publication number CN115418595B "Anti-cavitation-corrosion high-entropy alloy coating and preparation method thereof" discloses an Al-Cr-Co-Ni system high-entropy alloy coating. The coating has a high work hardening index and plastic deformation work, and therefore has excellent ability to absorb the impact energy of bubble collapse, and also has outstanding seawater corrosion resistance, so it is suitable for use as an anti-cavitation-corrosion coating in marine environments. However, the coating lacks sufficient solid lubrication properties, so its friction-reducing and wear-resistant performance in low-viscosity aviation kerosene is poor, especially in the condition of poor oil film on the surface of the component caused by high speed and high load, so the coating cannot be used as a protective coating for the surface of the friction pair of the fuel pump.

[0005] Because it is difficult to balance the anti-cavitation and lubrication wear resistance, there is no anti-cavitation and lubrication wear resistant coating suitable for aviation fuel pump reported at home and abroad. SUMMARY

[0006] In view of the problems in the above background art, the present application discloses an anti-cavitation and lubrication wear resistant high-entropy alloy coating and a preparation method thereof. The coating is suitable for the working condition environment of the friction pair of an aviation engine fuel pump and can maintain a low friction coefficient, wear rate and cavitation mass loss in low-viscosity aviation kerosene.

[0007] The technical solution adopted by the present application is as follows:

[0008] A preparation method of an anti-cavitation and lubrication wear resistant high-entropy alloy composite coating, comprising the following steps:

[0009] (1) Al-Cr-Co-Ni quaternary high-entropy alloy powder and Ag powder are weighed according to the mass percentage, and the powders are mixed uniformly in a mechanical mixer to obtain a spraying powder;

[0010] (2) The spraying powder obtained in step (1) is dried and then loaded into a powder feeder of a spraying device for standby;

[0011] (3) The surface of the metal substrate is sandblasted and cleaned, and then fixed on a spraying table;

[0012] (4) After setting the spraying process parameters, the hot spraying equipment is started, the powder is sent into the flame flow and sprayed and deposited on the surface of the metal substrate to obtain an anti-cavitation and lubrication wear resistant high-entropy alloy composite coating.

[0013] Preferably, the Al-Cr-Co-Ni quaternary high-entropy alloy powder and the Ag powder in step (1) have a spherical or near-spherical morphology, and the particle size range is 5-100 μm.

[0014] Further preferably, the mass percentage of the Al-Cr-Co-Ni quaternary high-entropy alloy powder in step (1) is 80.00-95.00%, and the mass percentage of the Ag powder is 5.00-20.00%.

[0015] More preferably, the atomic percentage of each element in the Al-Cr-Co-Ni quaternary high-entropy alloy powder in step (1) is Al 7.6-15%, Cr 21-30%, Co 20-29%, and Ni 31-40%. For specific preparation steps, see Chinese invention patent CN202210997311.4.

[0016] Preferably, the drying temperature in step (2) is 80-120℃, and the flowability of the powder after drying is 10-25 s / 50 g.

[0017] Preferably, the metal base material in step (3) is copper alloy, titanium alloy, aluminum alloy, stainless steel and the like, and the roughness of the metal base material surface after sand blasting treatment is greater than or equal to 1 μm.

[0018] Preferably, the thermal spraying equipment in step (4) is a supersonic flame spraying equipment, the fuel gas used is natural gas or kerosene, the combustion-supporting gas is oxygen or air, and the carrier gas is nitrogen, argon or helium.

[0019] Further preferably, the spraying parameters in step (4) are as follows: spraying distance 25-32 cm, gun moving speed 200-2000 mm / s, interpass distance 1-4 mm, powder feeding rate 10-80 g / min, compressed air pressure 100-120 MPa, compressed air flow rate 18-22 m 3 / h, oxygen pressure 160-180 MPa, oxygen flow rate 19-23 m 3 / h, fuel gas pressure 120-140 MPa, fuel gas flow rate 15-19 m 3 / h.

[0020] Further preferably, the thickness of the deposited coating in step (4) is 50-1000 μm.

[0021] The application uses mixed powders of single face-centered cubic structure (FCC) Al-Cr-Co-Ni quaternary high-entropy alloy and Ag, which have the same (111) crystal plane preferred orientation, as the spraying feedstock, and uses a supersonic flame spraying technology with a flame speed of 7-8 Mach to deposit and prepare a high-entropy alloy composite coating on the surface of a metal base material. The obtained coating is not only uniform and dense in structure, but also well retains the original phase and crystal structure of the two powders. Since the two metals have good temperature resistance and the same crystal structure, their properties are very similar, and their response behavior under external force is more matched: under the action of friction, the FCC phase is rich in slip system, which is easy to drive the crystal plane to slip, especially the solid lubricating phase Ag with good ductility, so it is easy to form a continuous lubricating film on the friction interface; under the impact of bubble collapse, both the Al-Cr-Co-Ni quaternary high-entropy alloy and Ag can absorb impact energy through plastic deformation to prevent interface cracking and material peeling. Therefore, the high-entropy alloy composite coating of the application has the functions of lubrication, wear resistance and anti-cavitation, has good protection ability in working conditions where cavitation and wear exist at the same time, and is suitable for application to the surface of mechanical parts such as aircraft engine fuel pumps. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM morphology and XRD pattern of the spraying powder of Example 1.

[0023] Figure 2SEM cross-sectional morphology, EDS surface distribution map of Ag element and XRD pattern of the high-entropy alloy composite coating prepared by the high-velocity oxy-fuel spraying technology of Example 1.

[0024] Figure 3 Load-displacement curves of the high-entropy alloy powder and the high-entropy alloy composition in the composite coating of Example 1.

[0025] Figure 4 Surface SEM morphologies of the high-entropy alloy composite coating prepared in Example 1 and the MoS2 / graphite-based bonded solid lubricating coating prepared in Comparative Example 3 after the friction and wear test in RP-3 aviation kerosene.

[0026] Figure 5 Surface SEM morphologies of the high-entropy alloy composite coating prepared in Example 1 and the MoS2 / graphite-based bonded solid lubricating coating prepared in Comparative Example 3 after the cavitation test in RP-3 aviation kerosene for 1 h.

[0027] Figure 6 Friction coefficients and cavitation cumulative mass loss curves of the high-entropy alloy composite coatings and the MoS2-based bonded solid lubricating coatings and the MoS2 / graphite-based bonded solid lubricating coatings prepared in Examples 1-3 and Comparative Examples 1-3 in RP-3 aviation kerosene. DETAILED DESCRIPTION

[0028] The application will be further explained in conjunction with the examples.

[0029] Example 1

[0030] (1) Al-Cr-Co-Ni high-entropy alloy powder and Ag powder were selected as raw materials, and were respectively formulated according to 90wt% and 10wt% of the mass percentage, and the particle size range of the two kinds of powders was 15-53 μm, wherein the atomic percentage of each element in the Al-Cr-Co-Ni high-entropy alloy powder was: Al 10.00%, Cr 28.00%, Co 28.00%, and Ni 34.00%; the above-mentioned ingredients were mixed uniformly in a mechanical mixer to obtain a spraying powder;

[0031] (2) The above-mentioned spraying powder was placed in an oven and baked at 100℃ for 1 h, and then was loaded into a powder feeder of a spraying device for standby;

[0032] (3) Copper alloy was used as a metal substrate, and the surface thereof was roughened by using a sand blasting machine so that the roughness was ≥1 μm, and then was cleaned by using acetone and was fixed on a spraying table;

[0033] (4) The spraying process parameters of the supersonic flame spraying equipment are set as follows: spraying distance is 27.5 cm, interval distance is 2 mm, gun moving speed is 800 mm / s, powder feeding rate is 25 g / min, air pressure is 110 MPa, air flow is 19.0 m 3 / h, oxygen pressure is 170 MPa, oxygen flow is 20.4 m 3 / h, natural gas pressure is 130 MPa, natural gas flow is 16.6 m 3 / h, start the spraying equipment, and spray and deposit the powder into the flame flow on the surface of the copper alloy substrate to obtain the anti-cavitation lubrication wear-resistant high-entropy alloy composite coating, and the coating thickness is about 500 μm;

[0034] (5) The MMW-1 vertical universal friction and wear tester in end face contact form is used to simulate the contact mode of the thrust bearing / gear friction pair of the fuel pump, and the friction and wear properties of the coating prepared in step (4) under the condition of room temperature, 20 N, 200 r / min are characterized, and the counter material is selected as a 5 mm diameter pin made of 2Cr3WMoV, which is the actual material of the fuel pump gear, and the test results are shown in Table 1, and the coating shows better lubrication and wear resistance than the existing bonded solid lubrication coating;

[0035] (6) The cavitation erosion mass loss of the high-entropy alloy composite coating prepared in step (4) in RP-3 aviation kerosene is tested by using the ultrasonic vibration cavitation erosion tester, and the results show that the cumulative mass loss after 10 h of cavitation erosion is significantly less than that of the existing bonded solid lubrication coating, as shown in Figure 6 , combined with the results of step (5), the coating shows very good anti-cavitation lubrication and wear resistance.

[0036] Example 2

[0037] (1) Al-Cr-Co-Ni high-entropy alloy powder and Ag powder are selected as raw materials, and the mass percentages are 94wt% and 6wt% respectively, and the particle size ranges of the two kinds of powders are both 15-53 μm, wherein the mass percentages of each element in the Al-Cr-Co-Ni high-entropy alloy powder are: Al 10.00%, Cr 28.00%, Co 28%, Ni 34%; the above ingredients are mixed uniformly in a mechanical mixer to obtain a spraying powder.

[0038] (2) The above spraying powder is placed in an oven and baked at 110℃ for 1 h, and then loaded into the powder feeder of the spraying equipment for use;

[0039] (3) Stainless steel is used as the metal substrate, and the surface is roughened by using a sand blasting machine to make the roughness ≥1 μm, and then cleaned with petroleum ether and fixed on the spraying table;

[0040] (4) Set the spraying process parameters of the supersonic flame spraying equipment as follows: spraying distance 27.5 cm, interpass distance 2 mm, gun moving speed 800 mm / s, powder feeding rate 25 g / min, air pressure 110 MPa, air flow rate 19.0 m 3 / h, oxygen pressure 170 MPa, oxygen flow rate 20.4 m 3 / h, natural gas pressure 130 MPa, natural gas flow rate 16.6 m 3 / h, start the spraying equipment, and spray and deposit the powder into the flame flow on the surface of the stainless steel substrate to obtain the anti-cavitation lubrication wear-resistant high-entropy alloy composite coating, and the coating thickness is about 400 μm;

[0041] (5) The MMW-1 vertical universal friction and wear tester in end face contact form is used to simulate the contact mode of the thrust bearing / gear friction pair of the fuel pump to characterize the friction and wear performance of the coating prepared in step (4) under the conditions of room temperature, 20 N, and 200 r / min, and the counter material is a 5 mm diameter pin made of 2Cr3WMoV, the actual material of the fuel pump gear, and the test results are shown in Table 1. The coating shows better lubrication and wear resistance than the existing bonded solid lubrication coating;

[0042] (6) The ultrasonic vibration cavitation erosion tester is used to test the cavitation erosion mass loss of the high-entropy alloy composite coating prepared in step (4) in RP-3 aviation kerosene, and the results show that the cumulative mass loss after 10 h of cavitation erosion is significantly less than that of the existing bonded solid lubrication coating, as shown in Figure 6 , combined with the results of step (5), the coating shows very good anti-cavitation lubrication and wear resistance.

[0043] Example 3

[0044] (1) Al-Cr-Co-Ni high-entropy alloy powder and Ag powder are selected as raw materials, and the mass percentages are 86wt% and 14wt% respectively. The particle size range of the two kinds of powders is 15-53 μm, and the mass percentage of each element in the Al-Cr-Co-Ni high-entropy alloy powder is: Al 10.00%, Cr 28.00%, Co 28%, and Ni 34%. The above ingredients are mixed uniformly in a mechanical mixer to obtain a spraying powder;

[0045] (2) The above spraying powder is placed in an oven and baked at 100℃ for 1.5 h, and then loaded into the powder feeder of the spraying equipment for use;

[0046] (3) Use stainless steel as the metal substrate, roughen the surface of the substrate to make the roughness ≥1 μm using a sandblasting machine, and then clean it with acetone and fix it on the spraying table;

[0047] (4) The spraying process parameters of the supersonic flame spraying equipment are set as follows: spraying distance 27.5 cm, interpass distance 2 mm, gun moving speed 800 mm / s, powder feeding rate 25 g / min, air pressure 110 MPa, air flow rate 19.0 m 3 / h, oxygen pressure 170 MPa, oxygen flow rate 20.4 m 3 / h, natural gas pressure 130 MPa, natural gas flow rate 16.6 m 3 / h, and the spraying equipment is started to spray and deposit the powder into the flame flow on the surface of the stainless steel substrate to obtain the anti-cavitation lubrication wear-resistant high-entropy alloy composite coating with a thickness of about 350 μm;

[0048] (5) The MMW-1 vertical universal friction and wear tester with end face contact is used to simulate the contact mode of the thrust bearing / gear friction pair of the fuel pump to characterize the friction and wear performance of the coating prepared in step (4) under the conditions of room temperature, 20 N and 200 r / min, and the counter material is a 5 mm diameter pin made of 2Cr3WMoV, the actual material of the fuel pump gear, and the test results are shown in Table 1. The coating shows better lubrication and wear resistance than the existing bonded solid lubrication coating;

[0049] (6) The cavitation erosion mass loss of the high-entropy alloy composite coating prepared in step (4) in RP-3 aviation kerosene is tested by using the ultrasonic vibration cavitation erosion tester, and the results show that the cumulative mass loss after 10 h of cavitation erosion is significantly less than that of the existing bonded solid lubrication coating, as shown in Figure 6 , in combination with the results of step (5), the coating shows very good anti-cavitation lubrication and wear resistance.

[0050] Comparative Example 1

[0051] (1) Al-Cr-Co-Ni high-entropy alloy powder and Ag powder are selected as raw materials, and the mass percentages are 98wt% and 2wt% respectively. The particle size of the two kinds of powders is 15-53 μm, and the mass percentages of the elements in the Al-Cr-Co-Ni high-entropy alloy powder are: Al 10.00%, Cr 28.00%, Co 28%, and Ni 34%. The above ingredients are mixed uniformly in a mechanical mixer to obtain a spraying powder;

[0052] (2) The above spraying powder is placed in an oven and baked at 100℃ for 1 h, and then loaded into the powder feeder of the spraying equipment for use;

[0053] (3) Stainless steel is used as the metal substrate, and the surface is roughened by using a sandblasting machine to make the roughness ≥1 μm, and then cleaned with acetone and fixed on the spraying table;

[0054] (4) Set the spraying process parameters of the supersonic flame spraying equipment as follows: spraying distance 27.5 cm, interpass distance 2 mm, gun moving speed 800 mm / s, powder feeding rate 25 g / min, air pressure 110 MPa, air flow 19.0 m 3 / h, oxygen pressure 170 MPa, oxygen flow 20.4 m 3 / h, natural gas pressure 130 MPa, natural gas flow 16.6 m 3 / h, start the spraying equipment, and spray and deposit the powder into the flame flow on the surface of the stainless steel substrate to obtain a composite coating, and the coating thickness is about 400 μm;

[0055] (5) The MMW-1 vertical universal friction and wear tester in end face contact form is used to simulate the contact mode of the friction pair of the fuel pump thrust bearing / gear to characterize the friction and wear performance of the coating prepared in step (4) under the condition of room temperature, 20 N, 200 r / min, and the counter material is selected as a 5 mm diameter pin made of the actual material 2Cr3WMoV of the fuel pump gear, and the test results are shown in Table 1. The coating shows poor friction and wear performance, and the friction coefficient and wear rate are obviously higher than those of the high-entropy alloy composite coating of the application. It is shown that even if the high-entropy alloy and Ag used to prepare the composite coating are the same as those of the application, but the ratio exceeds the range specified in the application, the tribological performance of the coating will be significantly deteriorated.

[0056] (6) The cavitation mass loss of the composite coating prepared in step (4) in RP-3 aviation kerosene is tested by using the ultrasonic vibration cavitation tester, and the results show that the cumulative mass loss of the coating after 10 h of cavitation is small, as shown in Figure 6 , combined with the results of step (5), the coating has strong cavitation resistance, but does not have good lubrication and wear resistance.

[0057] Comparative Example 2

[0058] (1) 1.5 g of epoxy resin, 20.0 g of polyamide-imide are added to 67.7 g of mixed solvent (N,N-dimethylformamide 75 vol%, 1-methyl-2-pyrrolidone 25 vol%), and the resin system is obtained after stirring to completely dissolve the epoxy resin and polyamide-imide. Then 10.8 g of MoS2 is added to the resin system, and the MoS2-based adhesive solid lubricating coating is obtained after stirring uniformly;

[0059] (2) The stainless steel is used as the metal substrate, the surface of the metal substrate is roughened by using a sand blasting machine to make the rust removal standard grade at least reach Sa 2.5 level, and then the metal substrate is cleaned by using acetone and fixed on a sample table;

[0060] (3) Load the paint from step (1) into the Steli spray gun and use the Steli spray gun to spray the paint evenly onto the surface of the metal substrate. Use multiple small sprays, and wait for the previous spray to dry before spraying the next one, until the required thickness is achieved.

[0061] (4) After the sample coated in step (3) has dried to room temperature, it is placed in an oven and cured at 170°C for 60 minutes. The thickness of the coating was measured to be approximately 22 μm using a Mini Test 1100 eddy current thickness gauge.

[0062] (5) The MMW-1 vertical universal friction and wear tester with end face contact was used to simulate the contact mode of the fuel pump thrust bearing / gear friction pair to characterize the friction and wear performance of the coating prepared in step (4) under the conditions of room temperature, 20N, and 200r / min. The mating material was a 5mm diameter pin made of 2Cr3WMoV, the actual material used in the fuel pump gear. The test results are shown in Table 1. The coating showed good lubrication performance, but its wear resistance was significantly worse than that of the high-entropy alloy composite coating of the present invention (Examples 1, 2, and 3).

[0063] (6) The cavitation mass loss of the coating prepared in step (4) in RP-3 aviation kerosene was tested using an ultrasonic vibration cavitation tester. The results showed that its cumulative mass loss after 10 hours of cavitation was significantly greater than that of the high-entropy alloy composite coating of the present invention (Examples 1, 2, and 3). See Figure 6 Based on the results of step (5), although the coating has good lubrication performance, it does not have good wear resistance and cavitation resistance.

[0064] Comparative Example 3

[0065] (1) First, prepare 64.2g of mixed solvent according to the ratio of 75vol% N,N-dimethylformamide and 25vol% 1-methyl-2-pyrrolidone. Then, add 25.0g of polyamide-imide to part of the mixed solvent and stir until it is completely dissolved to obtain a resin system. Then, put 8.1g MoS2 and 2.7g graphite into a ball mill jar, and add 1 to 2 times the total weight of the mixed solvent. After grinding for 48h, the dispersed material is obtained. Finally, add the dispersed material and the remaining solvent to the resin system and stir evenly to obtain MoS2 / graphite-based bonded solid lubricating coating.

[0066] (2) Stainless steel is used as the metal substrate. In order to enhance the bonding strength between the coating and the metal substrate, the surface is roughened by sandblasting to make its rust removal standard grade reach at least Sa 2.5. Then, it is cleaned with acetone and fixed on the sample stage.

[0067] (3) The paint of step (1) is loaded into a Stellpak spray gun, and the paint is uniformly sprayed on the surface of the metal substrate using the Stellpak spray gun in a way of multiple small spraying, and the next spraying is performed after the previous spraying is surface-dried until the desired thickness is reached;

[0068] (4) After the sample sprayed in step (3) is surface-dried at room temperature, it is placed in an oven for curing at 280°C, and the curing time is 60 min. The thickness of the coating is about 25 μm measured by a Mini Test 1100 type eddy current thickness gauge;

[0069] (5) The MMW-1 vertical universal friction and wear tester in an end face contact form is used to simulate the contact mode of the friction pair of the fuel pump thrust bearing / gear to characterize the friction and wear performance of the coating prepared in step (4) at room temperature, 20 N and 200 r / min, and the counter material is a 5 mm diameter pin made of the actual material 2Cr3WMoV of the fuel pump gear. The test results are shown in Table 1. The coating shows good lubricating performance, but the wear resistance is not as good as the high-entropy alloy composite coating (Examples 1, 2 and 3) of the application.

[0070] (6) The cavitation mass loss of the coating prepared in step (4) in RP-3 aviation kerosene is tested by using an ultrasonic vibration cavitation tester. The results show that the cumulative mass loss after 10 h of cavitation is significantly greater than that of the high-entropy alloy composite coating (Examples 1, 2 and 3) of the application, as shown in Figure 6 , combined with the results of step (5), the coating has good lubricating performance, but does not have good wear resistance and cavitation resistance.

[0071] Performance test and data analysis:

[0072] (1) The microstructure of the coating

[0073] Taking the sprayed powder and the high-entropy alloy composite coating prepared in Example 1 as an example, the morphology and phase composition of the sprayed powder and the coating prepared in the application are analyzed by using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD).

[0074] Figure 1 The SEM morphology and XRD pattern of the sprayed powder. It can be seen that the sphericity of the powder is good, and the particle size range is mainly distributed in the range of 15-53 μm, indicating that it has good fluidity. The XRD pattern can clearly observe the characteristic peaks of Al-Cr-Co-Ni high-entropy alloy and Ag, showing that the crystal structures of both are single FCC phase, and (111) is the preferred orientation of the crystal face.

[0075] Figure 2The SEM cross-section photo, the EDS surface distribution map of Ag element and the XRD pattern of the high-entropy alloy composite coating prepared by using the supersonic flame spraying process are given. It can be seen that the coating is very dense, and almost no obvious pore defects can be seen inside, the thickness of the coating is about 500 μm, and the interface between the coating and the substrate is combined very tightly; in addition, Ag is very uniformly distributed in the composite coating and exists independently, and is not solid-solved into the crystal structure of the high-entropy alloy, which indicates that the way of spraying the mixed powder by using the supersonic flame spraying process in the present application can obtain the composite coating with uniform and dense structure on the basis of not destroying the original phase of the powder. The XRD pattern of the coating also confirms the above results, the peak position and intensity of the characteristic peaks of the two components in the pattern are almost exactly the same as those of the sprayed powder, which indicates that the original phase and crystal structure of the sprayed powder can be really preserved into the composite coating by using the preparation process of the present application, which is beneficial to keeping good lubricating, wear-resistant and anti-cavitation properties of the coating in the process of friction and cavitation.

[0076] (2) Performance test of the coating

[0077] In order to better study the performance of the high-entropy alloy composite coating of the present application, the nanoindentation instrument is used to detect the mechanical property changes of the high-entropy alloy powder and the high-entropy alloy component in the coating, and the results are shown in Figure 3 The original nano-hardness and elastic modulus of the high-entropy alloy powder are as high as 4.937 GPa and 101.995 GPa respectively, which is mainly due to the strengthening effect of the special lattice distortion effect of the high-entropy alloy; compared with the powder, the mechanical properties of the high-entropy alloy component in the coating of Example 1 are further improved, and the nano-hardness and elastic modulus are 6.855 GPa and 212.653 GPa respectively, which is because the high-entropy alloy is in FCC phase, and the slip system therein is more, and it is easy to produce dislocation and twinning and other strengthening structures in the process of spraying the high-speed impact on the surface of the substrate, which indicates that the high-entropy alloy matrix in the composite coating of the present application also has the self-strengthening effect, which is beneficial to better improving the load capacity, impact resistance and wear resistance of the coating and the like.

[0078] The MMW-1 vertical universal friction and wear tester is used to carry out the friction and wear test of the four kinds of coatings of Example 1 and Comparative Examples 1-3 in RP-3 aviation kerosene according to the ASTM G99-17 standard, and the test conditions are as follows: room temperature, RP-3 aviation kerosene medium, load of 20 N, rotation speed of 200 r / min, and friction time of 14400 s. The detection results are shown in Table 1 and Figure 6

[0079] Table 1 Friction coefficient and wear rate of the high-entropy alloy composite coatings and MoS2-based bonded solid lubricating coatings and MoS2 / graphite-based bonded solid lubricating coatings prepared in Examples 1-3 and Comparative Examples 1-3 in RP-3 aviation kerosene.

[0080] ​

[0081] As shown in Table 1, the coefficient of friction of the composite coating in Example 1 is approximately 0.10, and the wear rate is almost zero, even exhibiting a slight "negative wear"; the coefficient of friction of the composite coating in Comparative Example 1 is approximately 0.21, and the wear rate is 1.85 × 10⁻⁶. -3 mm 3 / Nm, the lubrication and wear resistance properties of the coating in Comparative Example 2 are significantly worse than those in Example 1; the coefficient of friction of the coating in Comparative Example 2 is approximately 0.12, and the wear rate is 3.77 × 10. -6 mm 3 / Nm, and the lubrication and wear resistance properties were also worse than those of Example 1; the coefficient of friction of the coating in Comparative Example 3 was approximately 0.11, and the wear rate was 2.57 × 10. -6 mm 3 / Nm, and the lubrication and wear resistance are also worse than those of Example 1.

[0082] The surface morphology of the high-entropy alloy composite coating and the MoS2 / graphite-based bonded solid lubricating coating of the present invention after friction tests in RP-3 medium was observed using SEM, such as... Figure 4 As shown, the composite coating prepared in Example 1 formed a continuous shear lubrication film on the wear surface without obvious brittle spalling. This is due to the fact that all components in the composite coating are FCC structures with preferred (111) crystal orientation, which are easier to spread and form a film along the friction trajectory under the action of friction. On the other hand, it is due to the strong load-bearing capacity of the Al-Cr-Co-Ni high-entropy alloy matrix. In addition, the phenomenon of "coking" of aviation kerosene on the wear surface appeared in some areas, which is the reason for the slight "negative wear" of the coating. The wear surface of the MoS2 / graphite-based bonded solid lubricating coating in Comparative Example 3 showed a layered structure similar to scales and local cracking and spalling, indicating that the MoS2 / graphite in the coating can also slip under the action of frictional shear stress. Therefore, the lubrication performance is acceptable. However, the poor mechanical properties of the organic resin result in low load-bearing and tear resistance. Therefore, the wear resistance is not as good as the composite coating of the present invention.

[0083] Cavitation tests were conducted on four coatings in RP-3 aviation kerosene using an ultrasonic vibration cavitation testing machine according to GB / T 6383-2009 standard. The test conditions were: aviation kerosene temperature (25±2)℃, amplitude bar vibration frequency of 20kHz, amplitude of 50μm (peak-to-peak), distance between the lower end of the amplitude bar and the coating surface of 0.5mm, and distance between the sample surface and the liquid surface of 12mm. The surface SEM morphology of the high-entropy alloy composite coating of Example 1 and the MoS2 / graphite-based bonded solid lubricating coating of Comparative Example 3 after 1 hour of cavitation in RP-3 aviation kerosene was observed. Figure 5As shown, the surface peeling damage of the MoS2 / graphite-based bonded solid lubricating coating is very serious, which is mainly because the mechanical strength and temperature resistance of the organic resin in the coating are poor, and the coating cannot resist the mechanical impact and high temperature effect caused by bubble collapse, and the property difference between the organic resin and the inorganic filler in the coating is large, and the deformation is not coordinated under external force, and the phase interface is prone to cracking and peeling; the damage degree of the cavitation surface of the high-entropy alloy composite coating is much lighter, which shows that the anti-cavitation lubrication wear-resistant high-entropy alloy composite coating of the application can better resist the impact damage of the cavitation load because the temperature resistance of the two metal components is good, the deformation behavior under external force is consistent, and the energy absorption capacity is good.

[0084] The cumulative mass loss of the sample after cavitation for different times was weighed using a centesimal balance, and the results are shown in Table 2. Figure 6 As can be seen from Table 2, the cumulative mass loss of the high-entropy alloy composite coating of Example 1 after cavitation in RP-3 for 10h is only 0.4mg, which is significantly less than 11.1mg and 11.2mg of the MoS2-based bonded solid lubricating coating and the MoS2 / graphite-based bonded solid lubricating coating of Comparative Examples 2 and 3, showing very good anti-cavitation lubrication wear-resistant performance.

[0085] In summary, the application selects the mixed powder of Al-Cr-Co-Ni quaternary high-entropy alloy and Ag with the same crystal structure as the spraying powder, and uses the supersonic flame spraying technology to prepare a uniform and dense high-entropy alloy composite coating on the surface of a metal base, which not only avoids the problem of poor impact resistance and high temperature resistance caused by the use of organic resin in the prior art bonded solid lubricating coating, but also eliminates the problem of incoordination and mismatch in response to external force caused by the obvious property difference between organic and inorganic multi-phase. Under the working condition of coexistence of cavitation and sliding wear, the high-entropy alloy composite coating of the application not only can absorb impact energy through uniform plastic deformation, greatly prolong the life of cavitation resistance, but also the single FCC phase structure of the coating, especially the higher ductility of Ag, can also reduce the friction coefficient through shear slip, combined with the inherent lattice distortion effect of high-entropy alloy and the self-strengthening effect generated in the spraying process, the wear resistance is also outstanding. Compared with the existing MoS2-based and graphite-based bonded solid lubricating coatings, the high-entropy alloy composite coating of the application not only has better lubrication performance, but also has tens to hundreds of times higher wear resistance and anti-cavitation performance, so it can play a more significant comprehensive protection effect on the friction pair such as the thrust bearing / gear, and is expected to greatly improve the life, stability and working efficiency of important components such as the fuel pump of the aero-engine.

Claims

1. A method for preparing a cavitation resistant, lubricating, wear resistant, high-entropy alloy composite coating, characterized in that, Comprise the following steps: (1) according to the mass percentage of Al-Cr-Co-Ni quaternary high-entropy alloy powder and Ag powder, respectively, and the above-mentioned powder is placed in the mechanical mixer and mixed uniformly to prepare the spraying powder; The mass percentage of Al-Cr-Co-Ni quaternary high-entropy alloy powder is 80.00~95.00%, and the mass percentage of Ag powder is 5.00~20.00%; The atomic percentage of each element in Al-Cr-Co-Ni quaternary high-entropy alloy powder is Al 7.6~15%, Cr 21~30%, Co 20~29%, and Ni 31~40%; (2) the spraying powder obtained in step (1) is dried and loaded into the powder feeder of the spraying equipment for use; (3) the surface of the metal substrate is sandblasted and roughened and cleaned, and then fixed on the spraying table; (4) set the spraying process parameters, start the thermal spraying equipment, send the powder into the flame and spray deposit on the metal substrate surface to obtain the anti-erosion lubrication wear-resistant high-entropy alloy composite coating; The thermal spraying equipment is a supersonic flame spraying equipment, the fuel gas used is natural gas or kerosene, the combustion-supporting gas is oxygen or air, and the carrier gas is nitrogen, argon or helium.

2. The method of claim 1, wherein the method of preparing the anti-cavitation lubrication wear-resistant high-entropy alloy composite coating is characterized by: In step (1), the morphology of Al-Cr-Co-Ni quaternary high-entropy alloy powder and Ag powder is spherical or near-spherical, and the particle size range is 5~100μm.

3. The method of claim 1, wherein the method of preparing the anti-erosion lubrication wear-resistant high-entropy alloy composite coating is characterized by: In step (2), the drying temperature is 80~120℃, and the flowability of the powder after drying is 10~25s / 50g.

4. The method of claim 1, wherein the method of preparing the anti-erosion lubrication wear-resistant high-entropy alloy composite coating is characterized by: In step (3), the metal substrate is one of copper alloy, titanium alloy, aluminum alloy or stainless steel, and the roughness Ra of the metal substrate surface after sandblasting treatment is greater than or equal to 1μm.

5. The method of claim 1, wherein the method of preparing the anti-erosion lubrication wear-resistant high-entropy alloy composite coating is characterized by: The spraying parameters in step (4) are spraying distance 25-32 cm, gun moving speed 200-2000 mm / s, interval 1-4 mm, powder feeding rate 10-80 g / min, compressed air pressure 100-120 MPa, compressed air flow 18-22 m 3 / h, oxygen pressure 160-180 MPa, oxygen flow 19-23 m 3 / h, gas pressure 120-140 MPa, gas flow 15-19 m 3 / h.

6. The method of claim 1, wherein the method of preparing the anti-erosion lubrication wear-resistant high-entropy alloy composite coating is characterized by: In step (4), the thickness of the deposited coating is 50~1000μm.

7. An anti-erosion lubrication wear-resistant high-entropy alloy composite coating prepared by the method of any one of claims 1-6.

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