High-entropy alloy coating based on self-propagating reaction assisted laser directional energy deposition and preparation method of high-entropy alloy coating

Abstract

The invention relates to the technical field of preparation of high-entropy alloy coatings, in particular to a high-entropy alloy coating based on self-propagating reaction assisted laser directional energy deposition and a preparation method of the high-entropy alloy coating. The preparation method comprises the steps that self-propagating reaction raw material powder and high-entropy metal raw material powder are mixed to prepare composite powder; then loading the composite powder into a laser directional energy deposition system; and under the action of high-energy laser directional deposition, the self-propagating reaction raw material powder in the composite raw material is subjected to a self-propagating high-temperature synthesis reaction, reaction heat release assists laser directional energy deposition, and the high-entropy alloy coating with the high melting point and controllable components is prepared on the surface of the base material. The method is simple in process and convenient to operate, and the prepared high-entropy alloy coating is excellent in forming performance, high in bonding quality with a matrix, high in hardness, high in wear resistance and excellent in corrosion resistance, cost reduction and efficiency improvement of preparation of the high-entropy alloy coating can be achieved, and the high-entropy alloy coating has wide application prospects in the fields of part surface strengthening, surface repairing and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of high-entropy alloy coating preparation, and particularly to a high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition and a preparation method thereof. Background Art

[0002] High-entropy alloys are advanced alloy materials with broad application prospects. Their unique multi-principal element composition design and high-entropy effect, lattice distortion effect, sluggish diffusion effect, and cocktail effect, which are quite different from traditional alloys, endow them with excellent comprehensive properties. Traditional superalloys represented by nickel-based alloys will show significant softening above 1200 °C, making their service performance difficult to cope with complex working conditions. However, the service temperature of refractory high-entropy alloy coatings can be extended to above 1800 °C, filling the gap in ultra-high temperature structural materials.

[0003] The hardness of refractory high-entropy alloy coatings generally exceeds 5 GPa, far higher than that of traditional metal coatings. Their high-temperature strength performance is particularly prominent, far exceeding that of traditional nickel-based superalloys. Through the high-entropy effect and lattice distortion effect, refractory high-entropy alloy coatings can still maintain a single solid solution structure of BCC or FCC at high temperatures, avoiding performance degradation caused by phase transformation. In addition, refractory high-entropy alloys have excellent corrosion resistance, and their high hardness and anti-adhesive wear characteristics make them perform excellently in friction and wear environments. Finally, by adjusting the types and proportions of elements, the service performance of refractory high-entropy alloy coatings can be optimized specifically, showing significant advantages in extreme service environments.

[0004] Laser Directed Energy Deposition (LDED) technology is an advanced high-precision additive manufacturing technology. It synchronously melts metal powders or wires through a high-energy laser beam and deposits them layer by layer, with outstanding advantages of high precision, high flexibility, and strong material adaptability. It is particularly suitable for complex structure repair, functional gradient material preparation, and high-performance coating development. Its rapid solidification characteristics can significantly refine grains, improve material density and mechanical properties, and at the same time support in-situ composite of multiple materials, showing high-efficiency and low-cost manufacturing potential in coating preparation, high-precision and sophisticated component repair, etc.

[0005] Self-propagating High-temperature Synthesis (SHS) is a low-cost and high-efficiency advanced synthesis technology. It utilizes the highly exothermic reaction of the material system itself to achieve rapid self-sustaining synthesis, with outstanding advantages of high energy efficiency, fast reaction speed, and high product purity. It is particularly suitable for preparing ceramics, intermetallic compounds, and refractory materials. Its reaction temperature can reach 2000 - 4000 °C, enabling the direct synthesis of advanced materials with high melting points. At the same time, by regulating the raw material ratio and the propagation of the combustion wave, porous structures or functionally graded materials can be precisely designed, showing unique high-efficiency and low-cost manufacturing potential in the fields of coating preparation, surface strengthening and repair, etc. In addition, the self-propagating reaction technology does not require continuous external energy input, can reduce processing carbon emissions, and has obvious environmental protection advantages that cannot be ignored.

[0006] Compared with other common high-entropy alloys, refractory high-entropy alloys have the characteristics of high melting point and great processing difficulty. The processing energy density of traditional single laser direct energy deposition technology is limited, making it difficult to stably, efficiently, and high-quality and low-cost complete the preparation of refractory high-entropy alloy coatings. At the same time, traditional single self-propagating reaction technology is difficult to ensure the forming quality, performance stability, and service energy efficiency of refractory high-entropy alloy coatings.

[0007] Based on this, a high-entropy alloy coating based on self-propagating reaction-assisted laser direct energy deposition is provided. On the premise of ensuring good formability and bonding properties of the refractory high-entropy alloy coating, the preparation process of the refractory high-entropy alloy coating is simplified, the energy consumption throughout the preparation process is reduced, and the cost reduction and efficiency increase of the preparation of refractory high-entropy alloy coatings are realized, having a very broad application prospect. In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] One of the purposes of the present invention is to provide a preparation method of a high-entropy alloy coating based on self-propagating reaction-assisted laser direct energy deposition.

[0009] Another purpose of the present invention is to provide a high-entropy alloy coating based on self-propagating reaction-assisted laser direct energy deposition with high surface hardness, good wear resistance, and low coating porosity.

[0010] The technical solution adopted by the present invention to achieve the first purpose is: to provide a preparation method of a high-entropy alloy coating based on self-propagating reaction-assisted laser direct energy deposition. A composite powder composed of refractory high-entropy metal raw material powder and self-propagating reaction raw material powder is used to prepare a refractory high-entropy alloy coating on the surface of a substrate by the method of laser direct energy deposition.

[0011] In the preparation method provided by the present invention, the self-propagating reaction raw material powder in the composite powder is excited by high-energy laser, and spontaneously undergoes a self-propagating high-temperature synthesis reaction and releases heat. With the assistance of the high-temperature stable heat flow generated by the self-propagating high-temperature synthesis reaction, it promotes the uniform physical mixing of refractory high-entropy metal raw material powders at the atomic scale and the generation of a high-entropy stable solid solution structure driven by thermodynamics, realizing the high-quality and low-cost preparation of refractory high-entropy alloy coatings, and thus solving the problem that it is difficult to produce refractory high-entropy alloy coatings with high cost performance, large batches, and high quality by traditional single technical means.

[0012] Further, the refractory high-entropy metal raw material powder includes at least four of W, Ta, Mo, Nb, V, Hf, Ti, Zr, and Cr.

[0013] Further, the self-propagating reaction raw material powder includes: the self-propagating reaction core components Al and MgSO4, the process control agent MgO, the forming strengthening additives CaF2 and K3AlF6, and SiO2 which serves as both a process control agent and a forming strengthening additive. Among them, Al, as the core component of the self-propagating reaction, undergoes a self-propagating reaction with MgSO4 at high temperature, releasing a large amount of heat and driving the continuous progress of the self-propagating process, providing a high-energy and stable heat source input for the preparation of refractory high-entropy alloy coatings; MgSO4, as another core component of the self-propagating reaction, on the one hand promotes the continuous occurrence of the self-propagating reaction, and on the other hand, the introduction of MgSO4 greatly reduces the raw material cost of the self-propagating system. MgO and SiO2, as process control agents, can absorb part of the reaction heat, slow down the propagation speed of the combustion wave, control the reaction speed, limit the reaction process, and prevent the coating from cracking or the coating porosity from increasing due to too fast reaction. Further, in order to ensure the uniformity of the coating composition, ensure its good forming quality and excellent bonding performance, the self-propagating high-temperature synthesis system is coordinately regulated by the forming strengthening additives CaF2, SiO2, and K3AlF6. Among them, CaF2, as an efficient flux, significantly reduces the liquidus temperature of refractory components, improves the interfacial wettability by reducing the melt viscosity, and promotes the reaction kinetics process; SiO2 forms a silicate glass phase in situ at high temperature, and synergistically acts with the gaseous active substances KF - AlF3 generated by the thermal decomposition of K3AlF6 to construct a liquid slag phase with a gradient surface tension. According to Stokes' law, it accelerates the floating and separation of the molten slag, realizing the dynamic purification of the molten pool. This regulation strategy effectively inhibits the nucleation of micropores and the tendency of crack propagation by reducing the system supercooling degree and solidification shrinkage rate, significantly improves the interfacial metallurgical bonding strength of heterogeneous materials, and finally realizes the controllable preparation of coatings with high forming quality.

[0014] Furthermore, the addition amount of the self-propagating reaction raw material powder in the composite powder needs to be controlled within a reasonable range: when the amount of the self-propagating reaction raw material powder is too small, the heat generated is not sufficient to stably support the preparation of the refractory high-entropy alloy coating; while when the amount of the self-propagating reaction raw material powder is too large, not only is the composition of the refractory high-entropy alloy coating easily contaminated by the excessive self-propagating reaction powder system, but also the preparation cost of the refractory high-entropy alloy coating is increased. Preferably, in the composite powder, the content of the self-propagating reaction raw material powder is 31.2 wt.% - 50.8 wt.%.

[0015] In some preferred embodiments, by weight percentage, the composition of the composite powder is as follows: high-entropy metal raw material powder: W 13.2% - 20.9%, Ta 16.9% - 18.8%, Mo 8.2% - 10.0%, Nb 8.8% - 10.2%, V 4.4% - 6.6%; self-propagating reaction raw material powder: Al 16.5% - 18.7%, MgSO4 7.2% - 16.8%, MgO 0.9% - 1.8%, CaF2 4.2% - 8.6%, SiO2 1.4% - 2.9%, K3AlF6 1% - 2%; the average particle size of the composite powder is 40 - 60 μm.

[0016] In the above composite powder, the high-entropy alloy raw material powder is composed of W, Ta, Mo, Nb, and V. Among them, W and Nb elements can significantly improve the high-temperature strength and creep resistance of the alloy through solid solution strengthening and the formation of a stable BCC phase; Ta element can form a high-entropy BCC solid solution synergistically with W, and its excellent thermal stability can inhibit high-temperature grain coarsening and improve oxidation resistance at the same time; Mo element can improve the room-temperature hardness and high-temperature anti-softening ability of the coating; V element can inhibit grain boundary slip and reduce the alloy density at the same time. This composition design realizes the synergistic optimization of high-temperature strength, corrosion resistance, radiation resistance, and low-temperature toughness through multi-scale regulation, and can meet the requirements of various extreme service scenarios. By optimizing and adjusting the composition and ratio of the self-propagating reaction, the present invention can efficiently, spontaneously, and stably generate high heat energy, realize molten pool purification, ensure the consistency of the composition of the coating, ensure the excellent and stable forming quality of the coating, and has low economic cost and good environmental friendliness.

[0017] Furthermore, the preparation method of the composite powder includes: mixing the mixture of the refractory high-entropy metal raw material powder and the self-propagating reaction raw material powder with absolute ethanol according to a mass ratio of 1:3 - 5, stirring at a rotation speed of 30 - 50 r / min for 1 - 3 h, and then performing vacuum drying. Among them, the use of absolute ethanol can improve the fluidity of the powder in the composite powder and facilitate uniform mixing.

[0018] Preferably, the vacuum drying treatment includes putting the stirred composite powder into a vacuum drying oven, with a drying temperature of 45 - 60 °C and a drying time of 1 - 2 h.

[0019] Furthermore, the process parameters of the laser directed energy deposition include: setting the laser power to 1800 - 2400 W, the scanning speed to 12 - 15 mm / s, the powder feeding rate to 50 - 75 g / min, the overlapping rate of the traveling path to 30% - 40%, the laser focal length to 12 - 16 mm, and the spot diameter to 1 - 3 mm; using an inert gas to protect the whole process of laser directed energy deposition, with a gas flow rate of 400 - 500 L / h. Compared with the process parameters of conventional laser directed energy deposition, the laser power of the present invention is in a relatively high range, which is convenient for fully stimulating the self-propagating reaction and promoting the dynamic purification process of the molten pool, ensuring the preparation of high-quality refractory high-entropy alloy coatings; the powder feeding rate is in a relatively high range, which can fully supply the continuous and stable progress of the self-propagating reaction; the overlapping rate is reduced to 30% - 40%, which is in a relatively low range, facilitating the full progress of the self-propagating reaction and realizing the high-quality and high-purity preparation of refractory high-entropy alloy coatings.

[0020] The present invention combines the particularity of the composition and ratio of the composite powder, and specifically adjusts the process parameters of laser directed energy deposition to ensure that the exothermic self-propagating reaction and the energy deposition of refractory high-entropy alloy occur simultaneously, ensuring the preparation of high-quality refractory high-entropy alloy coatings.

[0021] Furthermore, before the laser directed energy deposition, the substrate is pretreated, including: grinding, sandblasting, cleaning, and drying. Preferably, the pretreatment includes: first, using a angle grinder to smooth the surface of the substrate and remove the surface oxide scale; second, performing sandblasting treatment to obtain a higher surface quality of the surface to be processed; then using acetone for cleaning; and finally drying for standby.

[0022] The technical solution adopted by the present invention to achieve the second object is: to provide a high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition, which is prepared by the preparation method according to the first object of the present invention; the thickness of the high-entropy alloy coating is 1.2 - 3.6 mm.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition provided by the present invention combines the exothermic self-propagating reaction system with the laser directed energy deposition additive manufacturing technology, and uses the high-temperature stable heat flow generated by the self-propagating reaction to achieve the high-quality and low-cost preparation of refractory high-entropy alloy coatings, solving the problem that it is difficult to produce high-cost-effective large-batch high-quality refractory high-entropy alloy coatings by traditional single technical means.

[0024] (2) The high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition provided by the present invention can proceed spontaneously throughout the process only by high-energy laser exciting the self-propagating reaction, with convenient operation, good processing technology, low processing cost, low energy consumption, and can reduce processing carbon emissions.

[0025] (3) The refractory high-entropy alloy coating prepared by the present invention has high hardness, excellent wear resistance, and strong corrosion resistance, and has excellent comprehensive properties. Among them, the surface hardness reaches 35.6 GPa, the friction coefficient does not exceed 0.4 under the condition of 1200 °C, and the wear rate is 6.5×10 -6 mm 3 N -1 m -1 , the oxidation weight gain does not exceed 0.15 mg / cm under the condition of 1200 °C 2 , the corrosion current density of the coating is 2.14×10 -8 A / cm 2 . The refractory high-entropy alloy coating prepared by the present invention has high density, good forming effect, no cracks, and the porosity is not higher than 1.12%. The refractory high-entropy alloy coating prepared by the present invention has excellent forming quality, forms excellent metallurgical bonding with the substrate, and its bonding strength is not lower than 419 Mpa. The preparation method of the present invention is simple, the preparation efficiency is high, the process cost is low, and it is convenient for operation and popularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the preparation of a high-entropy alloy coating by self-propagating reaction-assisted laser directed energy deposition provided by the present invention; Figure 2 is a schematic diagram of the processing path of self-propagating reaction-assisted laser directed energy deposition provided by an embodiment of the present invention; Figure 3 is a scanning electron microscope image of the bonding area between the WTaMoNbV refractory high-entropy alloy coating prepared in Example ۱ and the Q235 substrate; Among them, 1 - refractory high-entropy alloy coating; 2 - fusion line; 3 - Q235 substrate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0028] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0029] The present invention will be further described below in conjunction with specific embodiments, but it is not intended to limit the present invention.

[0030] In Examples 1-3 of the present invention, the composition of the composite powder (high-performance composite raw material powder) is shown in Table 1 below, and the process parameters of laser direct energy deposition in Examples 1-3 are shown in Table 2 below.

[0031] Table 1

[0032] Table 2

[0033] Example 1 This example provides a method for preparing a high-entropy alloy coating based on self-propagating reaction-assisted laser direct energy deposition, including the following steps: Step 1: Prepare and process the high-performance composite raw material powder: According to the self-propagating reaction system and the high-entropy alloy system, select raw material powders of 17.2 wt.% Al, 12.3 wt.% MgSO4, 1.5 wt.% MgO, 5.0 wt.% CaF2, 2.6 wt.% SiO2, 1.5 wt.% K3AlF6, 18.2 wt.% W, 18.0 wt.% Ta, 9.5 wt.% Mo, 9.2 wt.% Nb, and 5.0 wt.% V and mix them. The average particle size of the powder is 50 μm; then perform stirring treatment, add the mixed raw material powder and absolute ethanol to an explosion-proof planetary mixer according to a mass ratio of 1:4, and stir at a speed of 40 r / min for 2 h; then perform vacuum drying treatment, put the stirred high-performance composite raw material powder into a vacuum drying oven, the drying temperature is 54 °C, and the drying time is 1.5 h.

[0034] Step 2: Set the process parameters of laser direct energy deposition: Start the laser direct energy deposition system, set the laser power to 2100 W, the scanning speed to 14 mm / s, the powder feeding rate to 66 g / min, the overlapping rate of the travel path to 35%, the laser focal length to 14 mm, and the spot diameter to 2 mm; select argon as the inert gas used, and set the argon gas flow rate to 450 L / h.

[0035] Step 3: Pretreat the metal substrate: Use a angle grinder to polish the surface of the Q235 substrate smoothly to remove the surface oxide scale; secondly, perform sandblasting treatment to obtain a high-level surface quality of the surface to be processed; then clean it with acetone; finally, dry it for standby.

[0036] Step 4: Prepare a refractory high-entropy alloy coating on the surface of the substrate with the assistance of self-propagating high-temperature synthesis reaction. Preparation of refractory high-entropy alloy coating: Place the treated Q235 substrate in the working chamber. Then, place the high-performance composite raw material powder after mixing treatment into the laser directed energy deposition system. Next, set the laser deposition processing path to prepare a coating with a size specification of 50×30 mm. After that, introduce argon gas. Finally, start the laser directed energy deposition system to process and obtain a refractory high-entropy alloy coating with a thickness of 2.4 mm.

[0037] Use a scanning electron microscope (SEM) to characterize and observe the bonding area between the WTaMoNbV refractory high-entropy alloy coating prepared in Example 1 and the Q235 substrate and the microstructure of the coating, as Figure 3 shown.

[0038] The SEM characterization results show that: (1) No defects such as cracks, pores, and slag inclusions were observed in the coating area, indicating excellent forming quality of the refractory high-entropy alloy coating; (2) The contrast transition in the coating area is natural, and it has a good microstructure morphology, conforming to the solidification characteristics of high-entropy alloys; (3) The fusion interface between the coating and the substrate shows a continuous, smooth wavy morphology, and no irregular fluctuating deformation was observed, indicating that a high-quality metallurgical bond was formed between the coating and the substrate.

[0039] Example 2 This example provides a method for preparing a high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition, including the following steps: Step 1: Prepare and process the high-performance composite raw material powder. According to the self-propagating reaction system and the high-entropy alloy system, select raw material powders of 16.5 wt.% Al, 16.8 wt.% MgSO4, 0.9 wt.% MgO, 4.2 wt.% CaF2, 1.4 wt.% SiO2, 1.0 wt.% K3AlF6, 20.9 wt.% W, 16.9 wt.% Ta, 8.2 wt.% Mo, 8.8 wt.% Nb, and 4.4 wt.% V and mix them. The average particle size of the powder is 50 μm. Then, perform stirring treatment. Add the mixed raw material powder and absolute ethanol to an explosion-proof planetary mixer at a mass ratio of 1:5 and stir at a speed of 30 r / min for 2.5 h. After that, perform vacuum drying treatment. Put the stirred high-performance composite raw material powder into a vacuum drying oven, with a drying temperature of 45 °C and a drying time of 2 h.

[0040] Step 2: Set the process parameters of laser directed energy deposition: Start the laser directed energy deposition system, set the laser power to 1800 W, the scanning speed to 15 mm / s, the powder feeding rate to 50 g / min, the overlapping rate of the traveling path to 30%, the laser focal length to 12 mm, and the spot diameter to 1 mm; Select nitrogen (N2) as the protective gas used, and set the nitrogen gas flow rate to 400 L / h.

[0041] Step 3: Pretreat the metal substrate: Use a grinding machine to polish the surface of the Q235 substrate smoothly to remove the surface oxide scale; Secondly, perform sandblasting treatment to obtain a high-level surface quality of the surface to be processed; Then clean it with acetone; Finally, dry it for standby.

[0042] Step 4: Prepare a refractory high-entropy alloy coating on the surface of the substrate assisted by self-propagating high-temperature synthesis reaction: Place the treated Q235 substrate in the working chamber, secondly place the high-performance composite raw material powder after mixing treatment into the laser directed energy deposition system, then set the laser deposition processing path to prepare a coating with a size specification of 50×30 mm, and then introduce nitrogen gas; Finally, start the laser directed energy deposition system to process and obtain a refractory high-entropy alloy coating with a coating thickness of 1.2 mm.

[0043] Example 3 This example provides a method for preparing a high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition, including the following steps: Step 1: Prepare and process the high-performance composite raw material powder: According to the self-propagating reaction system and the high-entropy alloy system, select raw material powders of 18.7 wt.% Al, 7.2 wt.% MgSO4, 1.8 wt.% MgO, 8.6 wt.% CaF2, 2.9 wt.% SiO2, 2.0 wt.% K3AlF6, 13.2 wt.% W, 18.8 wt.% Ta, 10.0 wt.% Mo, 10.2 wt.% Nb, and 6.6 wt.% V and mix them. The average particle size of the powder is 50 μm; Then perform stirring treatment, add the mixed raw material powder and absolute ethanol to an explosion-proof planetary stirrer in a mass ratio of 1:3, and stir at a speed of 30 r / min for 1.5 h; Then perform vacuum drying treatment, put the stirred high-performance composite raw material powder into a vacuum drying oven, the drying temperature is 45 °C, and the drying time is 1 h.

[0044] Step 2. Set the process parameters of laser directed energy deposition: Start the laser directed energy deposition system, set the laser power to 2400 W, the scanning speed to 12 mm / s, the powder feeding rate to 75 g / min, the overlapping rate of the traveling path to 40%, the laser focal length to 16 mm, and the spot diameter to 3 mm; Select argon (Ar) as the inert gas used, and set the argon gas flow rate to 500 L / h.

[0045] Step 3. Pretreat the metal substrate: Use a grinding machine to polish the surface of the Q235 substrate smoothly to remove the surface oxide scale; Secondly, perform sandblasting treatment to obtain a high-level surface quality of the surface to be processed; Then clean it with acetone; Finally, dry it for standby.

[0046] Step 4. Prepare a refractory high-entropy alloy coating on the surface of the substrate assisted by self-propagating high-temperature synthesis reaction: Place the treated Q235 substrate in the working chamber, secondly place the high-performance composite raw material powder after mixing treatment into the laser directed energy deposition system, then set the laser deposition processing path to prepare a coating with a size specification of 50×30 mm, and then introduce argon gas; Finally, start the laser directed energy deposition system to process and obtain a refractory high-entropy alloy coating with a coating thickness of 3.6 mm.

[0047] Comparative Example This comparative example provides a method for preparing a high-entropy alloy coating by laser directed energy deposition, including the following steps: Step 1. Prepare the high-entropy alloy raw material powder: Mix the raw material powders of 35.4 wt.% W, 28.5 wt.% Ta, 13.8 wt.% Mo, 14.9 wt.% Nb, and 7.4 wt.% V, and put them into a vacuum drying oven. The drying temperature is 45°C and the drying time is 2 h; The average particle size of the powder is 50 μm.

[0048] Step 2. Set the process parameters of laser directed energy deposition: Start the laser directed energy deposition system, set the laser power to 1800 W, the scanning speed to 15 mm / s, the powder feeding rate to 50 g / min, the overlapping rate of the traveling path to 30%, the laser focal length to 12 mm, and the spot diameter to 1 mm; Select nitrogen (N2) as the protective gas used, and set the nitrogen gas flow rate to 400 L / h.

[0049] Step 3. Pretreat the metal substrate: Use a grinding machine to polish the surface of the Q235 substrate smoothly to remove the surface oxide scale; Secondly, perform sandblasting treatment to obtain a high-level surface quality of the surface to be processed; Then clean it with acetone; Finally, dry it for standby.

[0050] Step 4. Prepare a refractory high-entropy alloy coating on the substrate surface: Place the treated Q235 substrate in the working chamber. Next, place the high-entropy alloy raw material powder in the laser directed energy deposition system. Then, set the laser deposition processing path to prepare a coating with a size specification of 50×30 mm. Thereafter, introduce nitrogen gas. Finally, start the laser directed energy deposition system to process and obtain a refractory high-entropy alloy coating with a thickness of 1.2 mm.

[0051] Coating performance test The surface hardness, wear rate at 1200 °C, and porosity of the high-entropy alloy coatings prepared in Example 1 and the comparative example were tested respectively, and the test results are shown in Table 3 below.

[0052] Table 3

[0053] As can be seen from the above table, In the present invention, a refractory high-entropy alloy coating is prepared by a method of self-propagating reaction-assisted laser directed energy deposition. Compared with the conventional method of using only laser directed energy deposition, the surface hardness of the prepared WTaMoNbV refractory high-entropy alloy is increased by about 350%, and the wear rate at 1200 °C is reduced by two orders of magnitude. At the same time, compared with the comparative example, the refractory high-entropy alloy coating prepared in the present invention has a high density, good forming effect, no cracks, and a significantly reduced porosity.

[0054] Furthermore, the refractory high-entropy alloy coatings prepared in Examples 1-3 of the present invention also have the following properties: the friction coefficient does not exceed 0.4 at 1200 °C, and the oxidation weight gain does not exceed 0.15 mg / cm 2 , and the coating corrosion current density is 2.14×10 -8 A / cm 2 . In addition, the refractory high-entropy alloy coatings prepared in Examples 1-3 of the present invention have excellent forming quality, form an excellent metallurgical bond with the substrate, and the bonding strength is not less than 419 Mpa. The preparation method of the present invention is simple, has high preparation efficiency, low process cost, and is convenient for operation and promotion.

[0055] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. Those skilled in the art should be able to realize that all equivalent replacements and obvious changes made by using the content of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A preparation method of a high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition, characterized in that, A composite powder composed of refractory high-entropy metal raw material powder and self-propagating reaction raw material powder is used to prepare a refractory high-entropy alloy coating on the surface of a substrate by laser directed energy deposition.

2. The preparation method according to claim 1, characterized in that The refractory high-entropy metal raw material powder includes at least four of W, Ta, Mo, Nb, V, Hf, Ti, Zr, and Cr.

3. The preparation method according to claim 2, characterized in that, The self-propagating reaction raw material powder includes: self-propagating reaction core components Al and MgSO4, process control agent MgO, forming strengthening additives CaF2 and K3AlF6, and SiO2 which serves as both a process control agent and a forming strengthening additive.

4. The preparation method according to claim 3, characterized in that, In the composite powder, the content of the self-propagating reaction raw material powder is 31.2 wt.% - 50.8 wt.%.

5. The preparation method according to claim 4, characterized in that, By weight percentage, the composition of the composite powder is as follows: W 13.2% - 20.9%, Ta 16.9% - 18.8%, Mo 8.2% - 10.0%, Nb 8.8% - 10.2%, V 4.4% - 6.6%; Al 16.5% - 18.7%, MgSO4 7.2% - 16.8%, MgO 0.9% - 1.8%, CaF2 4.2% - 8.6%, SiO2 1.4% - 2.9%, K3AlF6 1% - 2%; the average particle size of the composite powder is 40 - 60 μm.

6. The preparation method according to claim 1, wherein The preparation method of the composite powder includes: mixing a mixture of refractory high-entropy metal raw material powder and self-propagating reaction raw material powder with absolute ethanol according to a mass ratio of 1:3 - 5, stirring at a rotation speed of 30 - 50 r / min for 1 - 3 h, and then performing vacuum drying.

7. The preparation method according to claim 1, characterized in that, The process parameters of laser directed energy deposition include: laser power of 1800 - 2400 W, scanning speed of 12 - 15 mm / s, powder feeding rate of 50 - 75 g / min, traveling path overlap rate of 30% - 40%, laser focal length of 12 - 16 mm, and spot diameter of 1 - 3 mm.

8. The preparation method according to claim 1, characterized in that, An inert gas is used to protect the whole process of laser directed energy deposition, and the gas flow rate is 400 - 500 L / h.

9. The preparation method according to claim 1, wherein Before laser directed energy deposition, the substrate is pretreated, including: grinding, sandblasting, cleaning, and drying.

10. A high-entropy alloy coating based on self-propagating reaction-assisted laser directed energy deposition, characterized in that, Obtained by the preparation method according to any one of claims 1 - 9; the thickness of the high-entropy alloy coating is 1.2 - 3.6 mm.

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