A refractory high-entropy alloy coating having a dual-phase microstructure and a method of making the same

Abstract

This invention relates to the field of TC4 titanium alloy surface modification technology, specifically to a refractory high-entropy alloy coating with a dual-phase microstructure and its preparation method. The specific technical solution involves: mixing Al, Cr, Nb, Ti, and V powders in a ball mill and pre-laying them onto the surface of a TC4 titanium alloy; then obtaining the high-entropy alloy coating through laser cladding technology. The coating obtained by the preparation method disclosed in this invention can form a metallurgical bond with the substrate, and the coating is free of obvious cracks and pores, exhibiting a relatively uniform macroscopic morphology; the coating's microstructure mainly consists of fine equiaxed crystals and dendritic structures. The high-entropy alloy coating obtained by this invention improves the hardness and high-temperature oxidation resistance of titanium alloys, giving it broader application prospects in aerospace, rail transportation, and marine vessels.

Description

Technical Field

[0001] This invention relates to the field of TC4 titanium alloy surface modification technology, specifically to a refractory high-entropy alloy coating with a dual-phase microstructure and its preparation method. Background Technology

[0002] Titanium alloys (such as TC4, or Ti6Al4V) possess high specific strength, good corrosion resistance, and excellent high-temperature mechanical properties, making them widely used in aerospace, marine engineering, biomedicine, and sporting goods. However, TC4 titanium alloys have inherent defects such as low hardness, poor wear resistance, and a high coefficient of friction, making them prone to adhesive wear during friction and wear processes. Furthermore, their high-temperature oxidation resistance is limited; the oxidation rate increases significantly when the service temperature exceeds 500–600℃, and the resulting rutile TiO2 oxide film has a loose structure and weak adhesion to the substrate, making it prone to cracking and peeling under thermal cycling or mechanical stress, further exacerbating substrate oxidation. These defects severely limit the engineering applications of TC4 titanium alloys under extreme conditions such as high temperature and high friction.

[0003] Since wear and oxidation failure of titanium alloys mostly originate on the surface, surface modification technology has become an effective means to improve their wear resistance and high-temperature oxidation resistance. Common methods include thermal spraying, vapor deposition, ion implantation, and nitriding, but each has its own problems such as insufficient bonding strength between the coating and the substrate, eggshell effect due to excessively thin coatings, limited strengthening depth, or coarsening of substrate grains due to high-temperature treatment. In contrast, laser cladding technology uses high-energy-density lasers as a heat source to prepare reinforced coatings on titanium alloy surfaces that form a metallurgical bond with the substrate, have high density, and low dilution rate. It also has advantages such as high raw material utilization and ease of automation, and has become an important technical direction for titanium alloy surface modification.

[0004] High-entropy alloys, due to their high-entropy effect, lattice distortion effect, hysteresis diffusion effect, and cocktail effect, exhibit excellent performance in terms of hardness, wear resistance, and high-temperature oxidation resistance, making them ideal material systems for laser cladding coatings. Among them, lightweight refractory high-entropy alloys, represented by Al-Cr-Nb-Ti-V, combine good high-temperature strength, oxidation resistance, and low density, making them particularly suitable for the aerospace field where lightweighting is required. However, existing equiatomic-ratio AlCrNbTiV high-entropy alloy coatings still suffer from low oxidation resistance and insufficient wear resistance, making it difficult to fully meet the requirements of extreme working conditions. Therefore, how to stably prepare lightweight high-entropy alloy coatings with high hardness, excellent wear resistance, and high-temperature oxidation resistance on the surface of TC4 titanium alloy is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a refractory high-entropy alloy coating with a dual-phase microstructure and its preparation method, which solves the problems of low surface strength and poor oxidation resistance of TC4.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a refractory high-entropy alloy coating with a dual-phase microstructure, comprising the following raw materials by mass percentage: Al: 9.9–10.2 wt.%; Cr: 19.0–19.5 wt.%; Nb: 34.3–34.8 wt.%; Ti: 16.8–17.7 wt.%; V: 17.7–18.9 wt.%.

[0007] Correspondingly, a method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure involves mixing and ball milling various raw materials to obtain uniform alloy powder, drying the alloy powder, pre-placing it on the surface of a substrate to form a pre-placing layer, and then performing laser cladding to obtain a high-entropy alloy coating.

[0008] Preferably, the Al, Cr, Nb, and V powders are atomized spherical powders with a purity of ≥99.99% and a particle size of 15–53 μm, and the Ti powder is 300-mesh powder with a purity of ≥99.99%.

[0009] Preferably, the ball mill rotation speed is 180-200 r / min, the ball-to-material ratio is 4:1, and the ball milling time is 4-6 h.

[0010] Preferably, during the ball milling process, the ball milling should be performed with the ball mill rotating forward for 20 to 30 minutes, then in reverse for 20 to 30 minutes, and then stopped for 10 to 15 minutes, and this cycle should be repeated 4 to 7 times.

[0011] Preferably, the drying temperature is 90°C and the holding time is 3-5 hours.

[0012] Preferably, the thickness of the pre-placed layer is 1.0 to 1.2 mm.

[0013] Preferably, the laser power is 1100–1200 W and the scanning speed is 250 mm / min. -1 The spot diameter is 3.5-4 mm, the overlap rate is 25%-50%, and the protective gas is argon with a purity of not less than 99.99% and a gas flow rate of not less than 16 L / min.

[0014] The present invention has the following beneficial effects: (1) The AlCrNbTiV high-entropy alloy coating prepared by the present invention forms a good metallurgical bond with the substrate, the substrate and the cladding layer have a high bonding strength, and the substrate has small thermal deformation and low dilution rate.

[0015] (2) The AlCrNbTiV high-entropy alloy cladding layer prepared by the present invention has a uniform microstructure of equiaxed crystals and dendrites, and the cladding layer has high hardness, wear resistance and high temperature oxidation resistance.

[0016] (3) The present invention uses laser cladding to prepare the coating, which is easy to achieve a high degree of automation, suitable for continuous operation, and the process stability is easy to control. Attached Figure Description

[0017] Figure 1 This is a cross-sectional macroscopic morphology image under an optical microscope in Example 1; Figure 2 This is a scanning morphology image of the dendrites in Example 2; Figure 3 The coating oxidation weight gain curve for Example 1; Figure 4 The surface morphology of Example 1 after 50 hours of oxidation and the surface morphology of the titanium alloy substrate after 10 hours of oxidation are shown. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0020] This invention provides a refractory high-entropy alloy coating with a dual-phase microstructure, comprising the following raw materials by mass percentage: Al: 9.9–10.2 wt.%; Cr: 19.0–19.5 wt.%; Nb: 34.3–34.8 wt.%; Ti: 16.8–17.7 wt.%; V: 17.7–18.9 wt.%.

[0021] This invention provides a method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure. This method solves the problems of low surface strength and poor oxidation resistance of TC4. The specific steps include the following aspects: (1) Based on the calculation of empirical parameters, it is determined that the AlCrNbTiV system can form a high-entropy alloy. See Table 1.

[0022] Table 1 Calculation results of characteristic parameters of alloy system

[0023] (2) Al, Cr, Nb, Ti, and V are ball-milled in a planetary ball mill to obtain a composite powder. The Al, Cr, Nb, and V powders are atomized spherical powders with a purity greater than or equal to 99.99% and a particle size of 15–53 μm. The Ti powder is a 300-mesh mechanically crushed powder with a purity greater than or equal to 99.99%. The ball milling method is dry milling, with a milling speed of 180–200 rpm, a ball-to-material ratio of 4:1, and a milling time of 4–6 h. During the ball milling process, the mill rotates forward for 20–30 min, then reverses for 20–30 min, and then stops for 10–15 min, repeating this cycle 4–7 times.

[0024] (3) Surface pretreatment of titanium alloy substrate: First, use 120-grit sandpaper to remove oxide scale, then use 400-grit sandpaper to polish the substrate surface to make it relatively bright, and then use alcohol ultrasonic cleaning and drying for later use. The substrate is Ti6Al4V(TC4).

[0025] (4) The ball-milled powder is placed in a drying oven and dried for a certain period of time at a temperature of 90°C for 3-5 hours. Then, the powder is pre-placed on the substrate surface to form a pre-placed powder layer with a thickness of 1.0-1.2 mm. Subsequently, a laser cladding experiment is performed to obtain a high-entropy alloy coating. The laser power is 1100-1200 W, and the scanning speed is 250 mm / min. -1 The spot diameter is 3.5-4 mm, the overlap rate is 25%-50%, and the protective gas is argon with a purity of not less than 99.99% and a gas flow rate of not less than 16 L / min.

[0026] The basic principle of this invention is as follows: Al is a light metallic element with an atomic radius close to that of titanium. Adding it to titanium alloys has a significant solid solution strengthening effect, enhancing the strength of the high-entropy alloy coating and thus improving the performance of the titanium alloy to a greater extent. Furthermore, Al helps the coating form a stable alumina film at high temperatures, providing better protection for the titanium alloy substrate. Cr provides corrosion resistance by forming a passivation film (mainly Cr2O3) on the alloy surface. This adhered oxide layer protects the substrate by limiting the entry of corrosive agents (such as oxygen or aggressive ions) into the metal surface. Nb is a high-temperature element with a high melting point, helping to maintain the strength and hardness of the alloy coating at high temperatures. Ti and V can improve the compatibility between the coating and the substrate titanium plate, reducing the difference in thermal properties between the coating and the substrate, and helping to reduce the tendency of the coating to become embrittled. Based on the four major effects of high-entropy alloys, this method uses powders of the above five components to manufacture the coating.

[0027] The present invention will be further described below with reference to specific embodiments.

[0028] Example 1 A method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure, specifically including the following steps: (1) The high entropy alloy material described in this embodiment is composed of five metal element powders: Al, Cr, Nb, Ti and V. The composition and mass percentage of each component are 9.97% Al, 19.21% Cr, 34.32% Nb, 17.68% Ti and 18.82% V. Each metal powder is weighed using an electronic balance and placed into a ball mill jar.

[0029] (2) Surface pretreatment of titanium alloy substrate: First, use 120-grit sandpaper to remove the oxide scale, then use 400-grit sandpaper to polish the substrate surface to make it brighter, and then use alcohol ultrasonic cleaning and drying for later use.

[0030] (3) Place the ball mill jar containing the mixed powder of Al, Cr, Nb, Ti and V into a planetary ball mill for ball milling. The ball milling method is dry grinding, the ball milling speed is 200 rpm, the ball-to-material ratio is 4:1, the ball milling time is 5 h, and the ball milling process is 20 min forward, 20 min reverse, and then 10 min stop. Repeat this cycle 6 times to obtain a uniform mixed powder.

[0031] (4) The ball-milled powder is placed in a drying oven and kept at 90°C for 3 hours. Then, the powder is pre-placed on the substrate surface to form a pre-layer with a thickness of 1.0 mm. Laser cladding is then performed, with a laser power of 1125 W and a scanning speed of 250 mm·min. -1 The light spot diameter is 4mm, the overlap rate is 25%, and the protective gas is argon with a gas flow rate of 16L / min.

[0032] The obtained cladding layer was cut to obtain a cross-section, which was then sanded and polished with 400-1500 grit sandpaper. The image was then taken using a scanning electron microscope. Figure 1 As shown, the coating has a complete macroscopic morphology and forms a good metallurgical bond with the substrate, with no obvious defects in the cladding layer. Hardness was measured at five points at different locations on both the substrate and the coating. After removing the maximum and minimum values, the average value was taken. The experimental results are shown in Table 2. The results show that the coating significantly improves the hardness of the TC4 substrate compared to the substrate.

[0033] Table 2 Hardness values ​​(HV) at different locations in the substrate and coating

[0034] The sample block with the cladding layer was cut into 15mm pieces, and the substrate surface was covered with high-temperature resistant adhesive, exposing only the coating portion. These pieces were placed in a crucible and subjected to a high-temperature oxidation test in air at 800℃. The crucible and sample were weighed at 5h, 10h, 15h, 20h, 30h, and 50h of oxidation. The weight gain per unit area of ​​the coating was then calculated based on the coating surface area. Figure 3 As shown. During the test, the oxide layer of the coating did not crack or peel off. After 50 hours of oxidation, the coating morphology is as follows. Figure 4 (a). However, after oxidizing the titanium alloy substrate under the same conditions for 10 hours, the oxide scale had already severely cracked and peeled off, see... Figure 4 (b)

[0035] Example 2 A method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure, specifically including the following steps: (1) The high entropy alloy material described in this embodiment is composed of five metal element powders: Al, Cr, Nb, Ti and V. The composition and mass percentage of each component are 9.97% Al, 19.21% Cr, 34.32% Nb, 17.68% Ti and 18.82% V. Each metal powder is weighed using an electronic balance and placed into a ball mill jar.

[0036] (2) Surface pretreatment of titanium alloy substrate: First, use 120-grit sandpaper to remove oxide scale, then use 400-grit sandpaper to polish the substrate surface to make it brighter, and then use alcohol ultrasonic cleaning and drying for later use.

[0037] (3) Place the ball mill jar containing the mixed powder of Al, Cr, Nb, Ti and V into a planetary ball mill for ball milling. The ball milling method is dry grinding, the ball milling speed is 200 rpm, the ball-to-material ratio is 4:1, the ball milling time is 5 h, and the ball milling process is 20 min forward, 20 min reverse, and then 10 min stop. Repeat this cycle 6 times to obtain a uniform mixed powder.

[0038] (4) The ball-milled powder is placed in a drying oven and kept at 90°C for 3 hours. Then, the powder is pre-placed on the substrate surface to form a pre-layer with a thickness of 1.0 mm. Laser cladding is then performed, with a laser power of 1125 W and a scanning speed of 250 mm·min. -1 The laser spot diameter is 4 mm, the overlap rate is 35%, and argon is used as the protective gas at a flow rate of 16 L / min. The dendrite scanning morphology is shown below. Figure 2 As shown, the left image is a secondary electron mode image, and the right image is a backscattered electron mode image. It can be seen from the images that large-sized dendritic laves phases are formed inside, increasing the microhardness of the coating.

[0039] The obtained cladding layer was cut to obtain a cross-section, which was then sanded and polished using 400-1500 grit sandpaper. Hardness was measured at five points at different locations on both the substrate and the coating. After removing the maximum and minimum values, the average value was taken. The experimental results are shown in Table 3. The results show that the coating significantly improved the hardness of the TC4 substrate compared to the substrate.

[0040] Example 3 A method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure, specifically including the following steps: (1) The high entropy alloy material described in this embodiment is composed of five metal element powders: Al, Cr, Nb, Ti and V. The composition and mass percentage of each component are 9.97% Al, 19.21% Cr, 34.32% Nb, 17.68% Ti and 18.82% V. Each metal powder is weighed using an electronic balance and placed into a ball mill jar.

[0041] (2) Surface pretreatment of titanium alloy substrate: First, use 120-grit sandpaper to remove oxide scale, then use 400-grit sandpaper to polish the substrate surface to make it brighter, and then use alcohol ultrasonic cleaning and drying for later use.

[0042] (3) Place the ball mill jar containing the mixed powder of Al, Cr, Nb, Ti and V into a planetary ball mill for ball milling. The ball milling method is dry grinding, the ball milling speed is 200 rpm, the ball-to-material ratio is 4:1, the ball milling time is 5 h, and the ball milling process is 20 min forward, 20 min reverse, and then 10 min stop. Repeat this cycle 6 times to obtain a uniform mixed powder.

[0043] (4) The ball-milled powder is placed in a drying oven and kept at 90°C for 3 hours. Then, the powder is pre-placed on the substrate surface to form a pre-layer with a thickness of 1.0 mm. Laser cladding is then performed, with a laser power of 1125 W and a scanning speed of 250 mm·min. -1 The light spot diameter is 4mm, the overlap rate is 50%, and the protective gas is argon with a gas flow rate of 16L / min.

[0044] The obtained cladding layer was cut to obtain a cross-section, which was then sanded and polished using 400-1500 grit sandpaper. Hardness was measured at five points at different locations on both the substrate and the coating. After removing the maximum and minimum values, the average value was taken. The experimental results are shown in Table 3. The results show that the coating significantly improved the hardness of the TC4 substrate compared to the substrate.

[0045] Table 3 Hardness values ​​(HV) at different locations on the substrate and coating

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A refractory high-entropy alloy coating with a dual-phase microstructure, characterized in that: By weight percentage, it includes the following raw materials: Al: 9.9~10.2 wt.%; Cr: 19.0~19.5 wt.%; Nb: 34.3~34.8 wt.%; Ti: 16.8~17.7wt.%; V: 17.7~18.9 wt.%.

2. A method for preparing a refractory high-entropy alloy coating with a dual-phase microstructure as described in claim 1, characterized in that: After mixing and ball milling the raw materials, a uniform alloy powder is obtained. The alloy powder is dried and pre-placed on the surface of the substrate to form a pre-placed layer. Then, laser cladding is performed to obtain a high-entropy alloy coating.

3. The preparation method according to claim 2, characterized in that: The Al, Cr, Nb, and V powders are atomized spherical powders with a purity of ≥99.99% and a particle size of 15–53 μm, and the Ti powder is 300-mesh powder with a purity of ≥99.99%.

4. The preparation method according to claim 2, characterized in that: The ball mill operates at a speed of 180–200 r / min, with a ball-to-material ratio of 4:1 and a milling time of 4–6 h.

5. The preparation method according to claim 2 or 4, characterized in that: During the ball milling process, the ball needs to rotate clockwise for 20-30 minutes, then counterclockwise for 20-30 minutes, and then stop for 10-15 minutes, repeating this cycle 4-7 times.

6. The preparation method according to claim 2, characterized in that: The drying temperature is 90℃, and the holding time is 3 to 5 hours.

7. The preparation method according to claim 2, characterized in that: The thickness of the pre-formed layer is 1.0 to 1.2 mm.

8. The preparation method according to claim 2, characterized in that: The laser power is 1100–1200 W, and the scanning speed is 250 mm / min. -1 The spot diameter is 3.5-4 mm, the overlap rate is 25%-50%, and the protective gas is argon with a purity of not less than 99.99% and a gas flow rate of not less than 16 L / min.

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