A high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure and a preparation method thereof

Abstract

The present invention relates to the technical fields of thermal spraying and surface nitriding, and particularly relates to a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure and a preparation method thereof, including: a NiCr bonding layer in the first layer, an AlCoCrNiMo high-entropy alloy transition layer in the second layer, an AlCoCrNiMoBSi high-entropy alloy functional layer in the third layer, and a nitriding modification layer in the fourth layer. The present invention prepares high-entropy alloy powders through step-by-step mechanical alloying and solution-aging treatment, significantly simplifying the preparation process compared with traditional methods. Based on the inherent anti-wear and heat-resistant corrosion characteristics of high-entropy alloys, an oxygen-kerosene supersonic flame spraying technology is used to prepare a coating system with gradient functions, and then a nitriding modification layer is formed through nitriding treatment. This multi-layer structure design not only achieves good transition and bonding strength between layers, but also has excellent thermal conductivity and significantly improves the anti-wear and heat-resistant corrosion performance of the coating.

Description

Technical Field

[0001] The present invention relates to the technical fields of thermal spraying and surface nitriding, and particularly relates to a multi-layered high thermal conductivity, anti-wear, heat-resistant corrosion high-entropy alloy coating and a preparation method thereof. Background Art

[0002] As a core device in the thermal power generation system, the boiler tube wall in a boiler is a key component for efficient heat transfer. Its main function is to quickly conduct heat to the water-cooling system to drive power generation by directly contacting with high-temperature flue gas and molten substances. Under the harsh working conditions of long-term exposure to temperatures above 600°C, sulfide corrosion media, and ash particle erosion on the surface of the boiler tube, thermal corrosion and high-temperature wear are extremely likely to occur. This not only reduces the heat conduction efficiency of the tube wall but also causes a decrease in the mechanical strength of the tube wall, leading to tube burst accidents and shortening the equipment maintenance cycle. Therefore, it is urgent to strengthen the surface of the boiler tube by preparing a protective coating with high thermal conductivity, anti-wear, and heat-resistant corrosion characteristics to improve its service performance and service life in a complex thermal environment.

[0003] The advantages of AlCoCrNiMo high-entropy alloy as a heat-resistant corrosion protective coating lie in its multi-principal element synergistic effect and microstructure design. Al and Cr jointly form a double-layer passivation film of Al2O3 / Cr2O3. Combining with the unique diffusion retardation effect of high-entropy alloy, it significantly inhibits the penetration of oxygen and corrosion media. The introduction of Mo further strengthens the denseness of the passivation film. In addition, the ordered phase in the AlCoCrNi-based high-entropy alloy can reduce lattice distortion and phonon scattering, thereby improving the thermal conductivity. Research shows that its room-temperature thermal conductivity is significantly better than that of traditional stainless steel. It is reported that elements B and Si in the alloy will preferentially oxidize to form B2O3, SiO2 or form composite oxides with other elements (such as Al, Cr) at high temperatures. Such oxide films have denseness and high stability and can also block the penetration of corrosive media. Therefore, introducing elements B and Si into the AlCoCrNiMo high-entropy alloy can further improve its anti-thermal corrosion performance. To address potential wear failure during service, a dense nitride layer is formed on the surface of the high-entropy alloy through nitriding treatment. Based on the multi-principal element characteristics of the high-entropy alloy, it promotes the formation of multi-component nitride phases and realizes solid solution strengthening and dispersion strengthening at the nanoscale, improving the bearing capacity of the nitride layer and inhibiting crack initiation and propagation, thereby enhancing the friction and wear performance of the material.

[0004] Since the AlCoCrNiMoBSi high-entropy alloy contains high melting point elements (such as Mo, 2623 °C, B, 2180 °C) and low melting point elements (such as Al, 660 °C, Si, 1414 °C). During smelting, high temperatures may cause low melting point elements such as Al and Si to volatilize, resulting in a deviation of the composition from the designed ratio. In addition, the preparation of traditional high-entropy alloy powders involves smelting and spray granulation, which has the disadvantages of strict process parameter requirements and high energy consumption, restricting the application of thermal sprayed high-entropy alloy coatings in the field of boiler tube protection. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of poor thermal conductivity, insufficient heat-resistant corrosion and friction and wear resistance of the protective coating for ordinary boiler tubes, and the high cost and complex process of preparing traditional high-entropy alloy powders, and provides a high-thermal-conductivity, anti-wear and heat-resistant corrosion high-entropy alloy coating with a multi-layer structure and its preparation method.

[0006] To achieve the above purpose, the present invention discloses a high-thermal-conductivity, anti-wear and heat-resistant corrosion high-entropy alloy coating with a multi-layer structure, and the multi-layer structure high-thermal-conductivity, anti-wear and heat-resistant corrosion high-entropy alloy coating includes a NiCr bonding layer in the first layer, an AlCoCrNiMo high-entropy alloy transition layer in the second layer, an AlCoCrNiMoBSi high-entropy alloy functional layer in the third layer, and a nitriding modification layer in the fourth layer.

[0007] The thickness of the NiCr bonding layer is 40 - 60 μm, the thickness of the AlCoCrNiMo high-entropy alloy transition layer is 60 - 80 μm, the thickness of the AlCoCrNiMoBSi high-entropy alloy functional layer is 160 - 200 μm, and the thickness of the nitriding modification layer is 2 - 3 μm.

[0008] The present invention also discloses a preparation method of the above multi-layer structure high-thermal-conductivity, anti-wear and heat-resistant corrosion high-entropy alloy coating, including the following steps:

[0009] S1, spraying NiCr powder on the surface of the sandblasted substrate by oxy-kerosene supersonic flame spraying to prepare a NiCr bonding layer;

[0010] S2, spraying the solution-treated and aged AlCoCrNiMo high-entropy alloy powder on the surface of the NiCr bonding layer by oxy-kerosene supersonic flame spraying to prepare an AlCoCrNiMo high-entropy alloy transition layer;

[0011] S3, spraying the solution-treated and aged AlCoCrNiMoBSi high-entropy alloy powder on the surface of the AlCoCrNiMo high-entropy alloy transition layer by oxy-kerosene supersonic flame spraying to prepare an AlCoCrNiMoBSi high-entropy alloy functional layer;

[0012] S4. Perform nitriding treatment on the surface of the polished and buffed AlCoCrNiMoBSi high-entropy alloy functional layer to obtain a high-thermal-conductivity, anti-wear, and heat-resistant-corrosion high-entropy alloy coating with a multi-layer structure.

[0013] In the said step S2 and step S3, the solution-aging treatment specifically includes the following steps:

[0014] A1. Place the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder in a vacuum heat treatment furnace, close the furnace lid, and evacuate the inside of the vacuum heat treatment furnace to below 10 -5 Pa;

[0015] A2. After evacuating to 10 -5 Pa, heat up at a heating rate of 10 °C / min to 1150 °C, and hold for 5 h to perform solution treatment on the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder. The solution treatment temperature is 1150 °C and the solution treatment time is 5 h;

[0016] A3. After the solution treatment is completed, cool down to 600 °C and hold for 4 h to perform aging treatment on the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder. The aging treatment temperature is 600 °C and the aging treatment time is 4 h;

[0017] A4. After the aging treatment is completed, keep the vacuum degree inside the furnace cavity and cool down to room temperature with the furnace to finally obtain AlCoCrNiMo high-entropy alloy powder or AlCoCrNiMoBSi high-entropy alloy powder.

[0018] In the said step A1, the preparation method of the AlCoCrNiMo alloy powder is as follows: First, ball-mill the elemental Cr and Mo powders for 25 h, then add the elemental Co powder and ball-mill for 35 h, and then add the elemental Al and Ni powders and ball-mill for 45 h; the molar ratio of the elemental powder elements of the AlCoCrNiMo alloy powder is Al:Co:Cr:Ni:Mo = 1:1:1:1:1, and the particle sizes of the elemental Al, Co, Cr, Ni, and Mo powders are 15 - 45 μm.

[0019] In the step A1, the preparation method of the AlCoCrNiMoBSi alloy powder is as follows: First, the elemental Cr and Mo powders are ball-milled for 25 h, then the elemental Co powder is added and ball-milled for 35 h, the elemental Al and Ni powders are added and ball-milled for 45 h, and then the elemental B and Si powders are added and ball-milled for 55 h; the molar ratio of the elemental powders of the AlCoCrNiMoBSi alloy powder is Al:Co:Cr:Ni:Mo:B:Si = 1:1:1:1:1:0.1:0.15. The particle sizes of the elemental Al, Co, Cr, Ni, and Mo powders are 15 - 45 μm, and the particle sizes of the elemental B and Si powders are 1 - 3 μm.

[0020] In the step S2, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 26 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and it is sprayed for 2 - 3 passes.

[0021] In the step S3, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 32 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and it is sprayed for 3 - 5 passes.

[0022] In the step S4, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 32 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and it is sprayed for 8 - 15 passes.

[0023] In the step S4, the specific steps of the nitriding treatment are as follows:

[0024] B1, Put the sample to be nitrided into the nitriding furnace and seal the furnace body; Before the formal nitriding, evacuate the nitriding furnace to below 5 Pa;

[0025] B2, Heating stage: After the nitriding furnace reaches the predetermined vacuum degree, adjust the nitrogen / hydrogen gas flow rate to make the gas pressure in the furnace 60 - 80 Pa, increase the power supply voltage to 450 V, and simultaneously introduce nitrogen / hydrogen gas flow. According to the arc state inside the nitriding furnace, slowly adjust the voltage and conduction ratio to make the temperature in the furnace rise and maintain a stable glow. When the temperature reaches 300 °C, turn on the furnace body cooling water to cool the furnace wall until the temperature rises to the preset temperature of 600 °C;

[0026] B3, Insulation stage: After the nitriding furnace reaches the preset temperature, control the voltage at 720 V, the nitrogen gas flow rate at 600 sccm, the hydrogen gas flow rate at 200 sccm, and the duty cycle at 3:1 to ensure the stability of the temperature and pressure in the furnace. The insulation stage lasts for 8 - 48 h;

[0027] B4, Cooling stage: After the insulation is completed, turn off the power supply and continue to introduce nitrogen / hydrogen gas, with the nitrogen gas flow rate at 600 sccm and the hydrogen gas flow rate at 200 sccm, to maintain the reducing atmosphere inside the nitriding furnace to prevent oxidation. Cool with the furnace, and finally obtain a high - thermal - conductivity, anti - wear, heat - resistant and corrosion - resistant high - entropy alloy coating with a multi - layer structure.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1. The AlCoCrNiMo high - entropy alloy powder and AlCoCrNiMoBSi high - entropy alloy powder prepared by the present invention through step - by - step mechanical alloying and solution - aging treatment achieve forced alloying of multi - element metals in the solid state by high - energy ball milling, avoiding the limitation of the traditional melting process on the melting point difference of components. During the step - by - step mechanical alloying process, the powder undergoes repeated cold welding - crushing to achieve nano - level uniform mixing, and then through solution - aging treatment, lattice distortion is eliminated and solid solution strengthening is formed, finally obtaining high - entropy alloy powder with a dual - phase BCC / FCC structure. Compared with the traditional melting + atomization granulation method, this process has the characteristics of simple process, environmental friendliness, and low cost;

[0030] 2. The present invention utilizes the high thermal conductivity and heat - resistant and corrosion - resistant properties of the high - entropy alloy itself to prepare a high - thermal - conductivity, anti - wear, heat - resistant and corrosion - resistant high - entropy alloy coating with a multi - layer structure on the surface of the boiler tube. Among them, the NiCr bonding layer has high compatibility with the substrate, can enhance the interfacial bonding strength, block the diffusion of substrate elements, and maintain the stability of the coating; the AlCoCrNiMo high - entropy alloy transition layer has similar composition to the AlCoCrNiMoBSi high - entropy alloy functional layer, can relieve interfacial stress, reduce the thermal expansion coefficient gradient difference, and inhibit the cracking or spalling of the functional layer;

[0031] 3. During the nitriding process of the present invention, the Al, Cr, and Mo elements in the AlCoCrNiMoBSi high-entropy alloy functional layer combine with nitrogen to form hard nitrides. These dense nitride layers, together with the oxide films (such as Al2O3 and Cr2O3, etc.) that may form during the friction process, have the characteristics of self-lubrication, high hardness, and hindering oxygen diffusion, and can achieve the effects of reducing friction and corrosion resistance. At the same time, nitrogen atoms diffuse into the coating and undergo atomic-level diffusion to form residual compressive stress. This metallurgical bonding and residual stress state inhibit the initiation and spalling of cracks, avoid the spalling of the nitrided layer, and thus achieve the long-term anti-wear and heat-resistant corrosion effects. Description of the Drawings

[0032] Figure 1 It is the SEM image of AlCoCrNiMoBSi alloy powder;

[0033] Figure 2 It is the SEM image of AlCoCrNiMoBSi high-entropy alloy powder;

[0034] Figure 3 It is the XRD image of AlCoCrNiMoBSi alloy powder and AlCoCrNiMoBSi high-entropy alloy powder;

[0035] Figure 4 It is the SEM image of the high-thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure;

[0036] Figure 5 It is Figure 4 The partial enlarged view of point A in

[0037] Figure 6 It is the schematic diagram of the structure of the high-thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure. Detailed Embodiments

[0038] The following further elaborates on the above and other technical features and advantages of the present invention in conjunction with the accompanying drawings.

[0039] Example 1

[0040] A preparation method of AlCoCrNiMoBSi high-entropy alloy powder includes first preparing AlCoCrNiMoBSi alloy powder by step-by-step mechanical alloying; and then subjecting the AlCoCrNiMoBSi alloy powder to solution-aging treatment to prepare AlCoCrNiMoBSi high-entropy alloy powder.

[0041] The step-by-step mechanical alloying preparation process of the above AlCoCrNiMoBSi alloy powder includes the following steps:

[0042] (1) First, weigh the elemental Al, Co, Cr, Ni, Mo, B, and Si powders used in the step-by-step mechanical alloying preparation of AlCoCrNiMoBSi alloy powder. The molar ratio of Al:Co:Cr:Ni:Mo:B:Si is 1:1:1:1:1:0.1:0.15, and calculate the total mass of these elemental powders.

[0043] (2) Pour the weighed elemental Cr and Mo powders into a ball mill, add mixed grinding balls into the ball mill, the size and mass ratio of the mixed grinding balls are 15mm:10mm:6mm:5mm=1:4:2:1, and the total mass ratio of the mixed grinding balls to the total mass of the elemental powders is 10:1; then seal the ball mill, and evacuate and fill the inside of the jar with argon gas, wherein the vacuum degree must be below 10Pa, and the argon gas filled is high-purity argon gas with a pressure of 0.2-0.3MPa, and the filling time is 15min.

[0044] (3) Place the ball mill jar in an omnidirectional planetary ball mill, set the ball mill speed to 220 rpm, and rotate forward for 10 minutes, stop for 2 minutes, reverse for 10 minutes, and stop for 2 minutes as one cycle. The ball milling time is 25 hours.

[0045] (4) After ball milling for 25 h, open the ball mill jar and pour in the weighed elemental Co powder. Then, seal, evacuate, and fill the ball mill jar with argon as in step (2), and then ball mill for 35 h according to the parameters of step (3).

[0046] (5) After ball milling for 35 h, open the ball mill and pour in the weighed Al and Ni powders. Then, seal, evacuate, and fill the ball mill with argon as in step (2). Then, ball mill for 45 h according to the parameters in step (3).

[0047] (6) After ball milling for 45 h, open the ball mill jar and pour in the weighed elemental B and Si powders. The ball mill jar is then sealed, vacuumed, and filled with argon as in step (2). The jar is then ball milled for 55 h according to the parameters of step (3).

[0048] (7) After the ball milling time is reached, the AlCoCrNiMoBSi alloy powder is taken out and the powder is sieved using a powder sieving machine and a metal screen equipped with an ultrasonic vibrator. The upper metal screen is 325 mesh and the lower metal screen is 800 mesh. The ultrasonic vibrator is installed on the lower metal screen. The sieving time is 30 minutes. Finally, AlCoCrNiMoBSi alloy powder with a particle size range of 15-45 μm is taken out from the lower screen.

[0049] The solution-aging treatment of the AlCoCrNiMoBSi alloy powder comprises the following steps:

[0050] (1) Place the AlCoCrNiMoBSi alloy powder prepared in the above steps in a corundum crucible and place it in a vacuum heat treatment furnace; close the furnace lid, turn on the mechanical pump and molecular pump to evacuate the inside of the furnace cavity to a vacuum of less than 10 -5 Pa.

[0051] (2) Solution treatment: After reaching the specified vacuum degree, heat it up to 1150 °C at a heating rate of 10 °C / min and hold for 5 h to perform solution treatment on the AlCoCrNiMoBSi alloy powder.

[0052] (3) Aging treatment: After reaching the solution treatment time, cool it down to 600 °C and hold for 4 h to perform aging treatment on the AlCoCrNiMoBSi alloy powder.

[0053] (4) After aging treatment, maintain the vacuum degree inside the furnace cavity (less than 10 -5 Pa), and cool it down to room temperature with the furnace to finally obtain AlCoCrNiMoBSi high-entropy alloy powder.

[0054] For the AlCoCrNiMoBSi alloy powder and AlCoCrNiMoBSi high-entropy alloy powder prepared in this example, use SEM to observe the cross-sectional microstructure of the powder, as Figure 1 shown; use XRD to detect the phase composition of the powder, as Figure 2 shown.

[0055] It can be seen from Figure 1 that the step-by-step mechanical alloying method can prepare elemental Al, Co, Cr, Ni, Mo, B and Si powders into uniformly distributed AlCoCrNiMoBSi alloy powders, and the AlCoCrNiMoBSi alloy powders have a spherical-like morphology and particle sizes suitable for thermal spraying. It can be seen from Figure 2 that the AlCoCrNiMoBSi high-entropy powder obtained after solution-aging treatment has similar sizes and shapes to the AlCoCrNiMoBSi alloy powder, but the elemental distribution inside the powder is more uniform. Figure 3 The phase analysis results of

[0056] Example 2

[0057] A high thermal conductivity, anti-wear and heat corrosion resistant high-entropy alloy coating with a multi-layer structure, as Figure 6As shown, from the bottom layer to the surface, it successively includes an oxygen-kerosene supersonic flame sprayed NiCr bonding layer, an AlCoCrNiMo high-entropy alloy transition layer, an AlCoCrNiMoBSi high-entropy alloy functional layer, and a nitriding modification layer.

[0058] The preparation processes of the above-mentioned oxygen-kerosene supersonic flame sprayed NiCr bonding layer, AlCoCrNiMo high-entropy alloy transition layer, and AlCoCrNiMoBSi high-entropy alloy functional layer include the following steps:

[0059] (1) Dry the NiCr powder, AlCoCrNiMo high-entropy alloy powder, and AlCoCrNiMoBSi high-entropy alloy powder to remove excess moisture. The drying temperature is 120 °C and the time is 20 min.

[0060] (2) Roughly sandblast the surface of the boiler steel. Use 24-mesh brown fused alumina sand, and the sandblasting carrier gas pressure is 0.5 - 0.7 MPa. After sandblasting, clean the substrate with anhydrous ethanol or acetone, and then preheat the substrate. The preheating temperature is 120 °C and the time is 15 min.

[0061] (3) Preparation of the NiCr bonding layer: The process parameters of oxygen-kerosene supersonic flame spraying include a kerosene flow rate of 26 m 3 / h, an oxygen flow rate of 53 m 3 / h, a spraying distance of 380 mm, a spraying step distance of 3 mm, a spray gun moving speed of 800 mm / s, a barrel size of 6 inches, a powder feeding rate of 50 g / min. Spray 2 passes, and the thickness of the NiCr bonding layer is 40 - 60 μm.

[0062] (4) Preparation of the AlCoCrNiMo high-entropy alloy transition layer: Directly perform oxygen-kerosene supersonic flame spraying on the surface of the NiCr bonding layer. The process parameters include a kerosene flow rate of 32 m 3 / h, an oxygen flow rate of 53 m 3 / h, a spraying distance of 380 mm, a spraying step distance of 3 mm, a spray gun moving speed of 800 mm / s, a barrel size of 6 inches, a powder feeding rate of 50 g / min. Spray 4 passes, and the thickness of the AlCoCrNiMo high-entropy alloy transition layer is 60 - 80 μm.

[0063] (5) Preparation of the AlCoCrNiMoBSi high-entropy alloy functional layer: Directly perform oxygen-kerosene supersonic flame spraying on the surface of the AlCoCrNiMo transition layer. The process parameters include a kerosene flow rate of 32 m 3 / h, an oxygen flow rate of 53 m 3 / h, spraying distance is 380 mm, spraying step distance is 3 mm, spray gun moving speed is 800 mm / s, barrel size is 6 inches, powder feeding rate is 50 g / min, spraying is carried out for 12 passes, and the thickness of the AlCoCrNiMoBSi functional layer is 160 - 200 μm.

[0064] The preparation process of the above nitriding modified layer includes the following steps:

[0065] (1) Before nitriding, the surface of the functional layer is polished, and the polished sample surface is thoroughly cleaned with absolute ethanol or acetone.

[0066] (2) The sample to be nitrided is placed in a nitriding furnace, and the furnace body is sealed; before formal nitriding, the nitriding furnace is evacuated to near vacuum (below 5 Pa).

[0067] (3) Heating stage: When the nitriding furnace reaches the predetermined vacuum degree, adjust the nitrogen / hydrogen gas flow rate to make the gas pressure value in the furnace 60 - 80 Pa, increase the power supply voltage to 450 V, and at the same time introduce nitrogen / hydrogen gas flow. According to the arc light state inside the nitriding furnace, slowly adjust the voltage and conduction ratio to make the temperature in the furnace rise and maintain a stable glow. When the temperature reaches 300 °C, turn on the furnace body cooling water to cool the furnace wall until the temperature rises to the preset temperature of 600 °C.

[0068] (4) Insulation stage: When the nitriding furnace reaches the preset temperature, control the voltage at 720 V, the nitrogen gas flow rate at 600 sccm, the hydrogen gas flow rate at 200 sccm, and the duty cycle at 3:1 to ensure the stability of the temperature and pressure in the furnace. The insulation stage lasts for 8 h respectively.

[0069] (5) Cooling stage: After reaching the preset insulation time, turn off the power supply, continue to introduce nitrogen / hydrogen gas, the nitrogen gas flow rate is 600 sccm, the hydrogen gas flow rate is 200 sccm, maintain the reducing atmosphere in the nitriding furnace to prevent oxidation, and cool with the furnace to finally obtain a multi-layered high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating.

[0070] For the multi-layered structure coating (before nitriding) prepared in this embodiment, a universal tensile testing machine is used to measure the bonding strength of the multi-layered structure coating, and a Vickers hardness tester is used to measure the microhardness and fracture toughness of the multi-layered structure coating. The results are shown in Table 1.

[0071] Table 1 Bonding strength and fracture toughness of the multi-layered structure coating

[0072]

[0073] As can be seen from Table 1, the bonding layer can significantly improve the bonding strength between the functional layer and the substrate. However, it has little effect on the microhardness and fracture toughness of the modified layer. The composition of the transition layer is similar to that of the functional layer, which can improve the bonding strength of the functional layer to a certain extent. In addition, due to the supporting effect of the transition layer, the microhardness and fracture toughness of the double-layer structure coating of the transition layer + functional layer are significantly improved compared with the single-layer functional layer. The three-layer structure coating of the bonding layer + transition layer + functional layer combines the characteristics of the bonding layer and the transition layer, and the bonding strength, microhardness and fracture toughness of the coating are all significantly improved.

[0074] Example 3

[0075] The difference between this example and Example 2 is that in step (4) of the preparation process of the nitrided modified layer, the holding stage lasts for 16 h, and other process steps are the same as those in Example 2.

[0076] Example 4

[0077] The difference between this example and Example 2 is that in step (4) of the preparation process of the nitrided modified layer, the holding stage lasts for 32 h, and other process steps are the same as those in Example 2.

[0078] Example 5

[0079] The difference between this example and Example 2 is that in step (4) of the preparation process of the nitrided modified layer, the holding stage lasts for 48 h, and other process steps are the same as those in Example 2.

[0080] Performance tests were carried out on the multi-layer structure coatings nitrided at different times (8 h, 16 h, 32 h, 48 h) prepared in Examples 2 to 5: a laser thermal conductivity analyzer was used to measure the thermal conductivity of the coatings at different temperatures, a pin-on-disk friction and wear tester was used to measure the friction and wear performance of the coatings at 700 °C, and a precision balance was used to evaluate the weight gain of the coatings after 100 h of thermal corrosion; SEM was used to observe the cross-section of the high thermal conductivity, wear-resistant and heat-resistant corrosion high-entropy alloy coating of the multi-layer structure after nitriding for 16 h, as Figure 4 and Figure 5 shown.

[0081] Figure 4 is the overall morphology diagram of the multi-layer structure coating. The coating is dense inside and has no pores. The interfaces of the multi-layer coatings are well combined. The thickness of the NiCr bonding layer is 62 μm, the thickness of the AlCoCrNiMo high-entropy alloy transition layer is 84 μm, and the thickness of the AlCoCrNiMoBSi high-entropy alloy functional layer is 162 μm. Figure 5 is the enlarged view near the top of the multi-layer structure coating. After the nitriding surface modification treatment, a continuous and dense nitrided modified layer is formed on the coating surface, and its thickness is 2.33 μm. Figure 6Shown is a schematic diagram of the multi-layer structured coating.

[0082] The thermal conductivity of the coating at different temperatures is shown in Table 2:

[0083] Table 2 Thermal conductivity of the coating at different temperatures

[0084]

[0085] As can be seen from Table 2, the thermal conductivity of the multi-layer structured coating at room temperature is 8.86 W∙(m∙K) -1 , and as the test temperature increases, the thermal conductivity of the multi-layer structured coating gradually increases, reaching 19.89 W∙(m∙K) at 700 °C -1 , which can reach more than 80% of the thermal conductivity of the boiler steel substrate (21.13 W∙(m∙K) at 700 °C -1 ). After nitriding the multi-layer structured coating for 8 h and 16 h, the thermal conductivities at room temperature and 700 °C are comparable to those of the non-nitrided coating, indicating that the nitrided layer obtained under these nitriding parameters has little effect on the thermal conductivity of the multi-layer structured coating. When the nitriding time reaches 32 h and 48 h, the thermal conductivity of the coating decreases significantly, and the thermal conductivity at 700 °C is only below 51% of the thermal conductivity of the boiler steel substrate, unable to meet the requirement of high thermal conductivity.

[0086] The friction coefficient and wear rate of the coating at 700 °C are shown in Table 3 below:

[0087] Table 3 Friction coefficient and wear rate of the coating at 700 °C

[0088]

[0089] As can be seen from Table 3, after the multi-layer structured coating is nitrided for 16 h, the friction coefficient and wear rate are 0.27 and 3.72×10 -5 mm 3 ∙(N∙m) -1 respectively, showing better anti-friction and wear-resistant effects compared to the non-nitrided coating. When the nitriding time reaches 32 h and 48 h, the friction coefficient and wear rate increase slightly, but both are better than those of the non-nitrided coating.

[0090] The thermal corrosion weight gain and thermal corrosion weight gain kinetic constant at different nitriding times are shown in Table 4 below:

[0091] Table 4 Thermal corrosion weight gain and thermal corrosion weight gain kinetic constant at different nitriding times

[0092]

[0093] As can be seen from Table 4, the weight gain and kinetic constant of the AlCoCrNiMoBSi high-entropy alloy multi-layer structure coating after 16 h of nitriding treatment are 4.67 mg∙cm -2 and 0.43 mg 2 ∙cm -4 ∙h -1 , respectively. The heat-resistant corrosion performance is several times higher than that of the un-nitrided coating. When the nitriding time reaches 32 h and 48 h, the heat-resistant corrosion performance of the coating is better than that of the un-nitrided coating.

[0094] Based on the comprehensive tests of the thermal conductivity, friction and wear, and heat-resistant corrosion performance of the multi-layer structure coating before and after nitriding, the following conclusions can be drawn: The multi-layer structure high-entropy alloy coating obtained after 16 h of nitriding treatment can significantly improve its friction and wear performance and heat-resistant corrosion performance while taking into account the high thermal conductivity.

[0095] The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure, characterized in that, The high thermal conductivity, wear-resistant, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure includes a NiCr bonding layer in the first layer, an AlCoCrNiMo high-entropy alloy transition layer in the second layer, an AlCoCrNiMoBSi high-entropy alloy functional layer in the third layer, and a nitriding modification layer in the fourth layer.

2. The high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 1, characterized in that, The thickness of the NiCr bonding layer is 40 - 60 μm, the thickness of the AlCoCrNiMo high-entropy alloy transition layer is 60 - 80 μm, the thickness of the AlCoCrNiMoBSi high-entropy alloy functional layer is 160 - 200 μm, and the thickness of the nitriding modification layer is 2 - 3 μm.

3. A method for preparing a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure as described in claim 1 or 2, characterized in that, It includes the following steps: S1. On the surface of the sandblasted substrate, spray NiCr powder by oxy-kerosene supersonic flame to prepare the NiCr bonding layer. S2. On the surface of the NiCr bonding layer, spray the solution-treated and aged AlCoCrNiMo high-entropy alloy powder by oxy-kerosene supersonic flame to prepare the AlCoCrNiMo high-entropy alloy transition layer. S3. On the surface of the AlCoCrNiMo high-entropy alloy transition layer, spray the solution-treated and aged AlCoCrNiMoBSi high-entropy alloy powder by oxy-kerosene supersonic flame to prepare the AlCoCrNiMoBSi high-entropy alloy functional layer. S4. Perform nitriding treatment on the surface of the polished AlCoCrNiMoBSi high-entropy alloy functional layer to obtain the high thermal conductivity, wear-resistant, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure.

4. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 3, characterized in that, In the steps S2 and S3, the solution treatment and aging treatment specifically include the following steps: A1, Place the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder in a vacuum heat treatment furnace, close the furnace lid, and evacuate the inside of the vacuum heat treatment furnace to below 10 -5 Pa; A2, evacuate to 10 -5 Pa, then heat at a heating rate of 10 °C / min to 1150 °C and hold for 5 h to perform solution treatment on the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder. The solution treatment temperature is 1150 °C and the solution treatment time is 5 h; A3. After the solution treatment is completed, cool down to 600 °C and keep it warm for 4 h to perform aging treatment on the AlCoCrNiMo alloy powder or AlCoCrNiMoBSi alloy powder. The aging treatment temperature is 600 °C and the aging treatment time is 4 h. A4. After the aging treatment is completed, keep the vacuum degree inside the furnace chamber and cool it down to room temperature with the furnace to finally obtain the AlCoCrNiMo high-entropy alloy powder or AlCoCrNiMoBSi high-entropy alloy powder.

5. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 4, characterized in that, In the step A1, the preparation method of the AlCoCrNiMo alloy powder is as follows: First, ball-mill the elemental Cr and Mo powders for 25 h, then add the elemental Co powder and ball-mill for 35 h, and then add the elemental Al and Ni powders and ball-mill for 45 h. The molar ratio of the elemental powder elements of the AlCoCrNiMo alloy powder is Al:Co:Cr:Ni:Mo = 1:1:1:1:1, and the particle size of the elemental Al, Co, Cr, Ni, and Mo powders is 15 - 45 μm.

6. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure as claimed in claim 4, characterized in that, In the step A1, the preparation method of the AlCoCrNiMoBSi alloy powder is as follows: First, the elemental Cr and Mo powders are ball-milled for 25 h, then the elemental Co powder is added and ball-milled for 35 h, the elemental Al and Ni powders are added and ball-milled for 45 h, and then the elemental B and Si powders are added and ball-milled for 55 h; the molar ratio of the elemental powders of the AlCoCrNiMoBSi alloy powder is Al:Co:Cr:Ni:Mo:B:Si = 1:1:1:1:1:0.1:0.15, the particle sizes of the elemental Al, Co, Cr, Ni, and Mo powders are 15 - 45 μm, and the particle sizes of the elemental B and Si powders are 1 - 3 μm.

7. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 3, characterized in that, In the step S1, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 26 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and the spraying is carried out for 2 passes.

8. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 3, characterized in that, In the step S2, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 32 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and the spraying is carried out for 4 passes.

9. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 3, characterized in that In the step S3, the process parameters of the oxygen-kerosene supersonic flame spraying are as follows: the kerosene flow rate is 32 m 3 / h, the oxygen flow rate is 53 m 3 / h, the spraying distance is 380 mm, the spraying step distance is 3 mm, the moving speed of the spray gun is 800 mm / s, the barrel size is 6 inches, the powder feeding rate is 50 g / min, and the spraying is carried out for 12 passes.

10. The preparation method of a high thermal conductivity, anti-wear, heat-resistant and corrosion-resistant high-entropy alloy coating with a multi-layer structure according to claim 3, characterized in that, In the step S4, the specific steps of the nitriding treatment are as follows: B1, Place the sample to be nitrided in a nitriding furnace and seal the furnace body; evacuate the nitriding furnace to below 5 Pa before formal nitriding; B2, Heating stage: When the nitriding furnace reaches the predetermined vacuum degree, adjust the nitrogen / hydrogen gas flow rate to make the gas pressure in the furnace 60 - 80 Pa, increase the power supply voltage to 450 V, and simultaneously introduce the nitrogen / hydrogen gas flow. According to the arc light state inside the nitriding furnace, slowly adjust the voltage and conduction ratio to make the temperature in the furnace rise and maintain a stable glow discharge. When the temperature reaches 300 °C, turn on the furnace wall cooling water to cool the furnace wall until the temperature rises to the preset temperature of 600 °C; B3, Insulation stage: When the nitriding furnace reaches the preset temperature, control the voltage at 720 V, the nitrogen gas flow rate at 600 sccm, the hydrogen gas flow rate at 200 sccm, and the duty cycle at 3:1 to ensure the stability of the temperature and pressure in the furnace. The insulation stage lasts for 8 - 48 h; B4, Cooling stage: After the insulation is completed, turn off the power supply and continue to introduce nitrogen / hydrogen gas, with the nitrogen gas flow rate at 600 sccm and the hydrogen gas flow rate at 200 sccm, to maintain the reducing atmosphere in the nitriding furnace to prevent oxidation. Cool with the furnace to finally obtain a multi-layered high-thermal-conductivity, anti-wear, heat-resistant, and corrosion-resistant high-entropy alloy coating.

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