Ta10W (a tantalum alloy containing 10% tungsten) has a single-phase solid solution structure, with tungsten atoms uniformly distributed in the body-centered cubic lattice of tantalum. Its microstructure exhibits uniform equiaxed grains (after annealing), typically 5-20 μm in size, with no obvious second-phase precipitation, thus possessing both high strength and good plasticity (elongation can reach 15-20%). The elements contained in tantalum and its alloys have high melting points, and Ta has a strong affinity for interstitial elements (H, O, C, N). Traditional melting methods easily form interstitial solid solution phases or compound phases in the tantalum or tantalum alloy microstructure, deteriorating the material's properties. Therefore, the application of traditional casting methods in the preparation of refractory alloys is relatively limited.
To address the above characteristics of refractory alloys, domestic and international researchers mainly employ powder metallurgy, vacuum electron beam melting, and additive manufacturing technologies to prepare high-performance Ta and Ta alloys. Tantalum-10-tungsten alloy possesses high high-temperature strength, good ductility, weldability, and excellent corrosion resistance, making it suitable for high-temperature, high-pressure, and corrosion-resistant working environments. It is widely used in chemical, aerospace, energy industries, and high-temperature components. However, Ta10W alloy exhibits relatively poor high-temperature oxidation resistance under atmospheric conditions. At 500°C, Ta10W alloy shows "pest" oxidation, with the oxidation intensifying at higher temperatures until complete "pulverization" and destruction. A slurry melting process at 1500°C~1600°C for 10-30 minutes was used to prepare a silicide coating with good thermal stability and high-temperature oxidation resistance on the alloy surface. This coating protects the alloy substrate from high-temperature corrosion or slows down the corrosion rate, maintaining the alloy substrate composition and retaining at least 90% of the original substrate strength and at least 10% elongation at room temperature. Observation and analysis revealed that static oxidation failure of the silicide coating on the alloy surface was caused by continuous oxidation and peeling of the coating, while thermal shock oxidation failure was caused by microcracks formed due to the difference in thermal expansion coefficients between the coating and the substrate. The closer the coefficients of thermal expansion between the coating and the substrate, the better the coating's thermal shock resistance.
Currently, the main methods to improve the high-temperature oxidation resistance of tantalum-tungsten alloys under atmospheric conditions are alloying protection and surface coating protection. Alloying can improve the alloy's oxidation resistance, but the alloying elements must exceed a certain critical value to protect the substrate, inevitably affecting other alloy properties, especially causing a decrease in the high-temperature mechanical properties of the substrate. Therefore, alloying has its limitations. Adding a coating to the alloy surface can protect the alloy substrate from high-temperature corrosion or slow down the corrosion rate, maintaining the alloy substrate composition and ensuring that the substrate strength at room temperature is not less than 90% of the original substrate strength and the elongation is not less than 10%.
Using elemental powders with a purity of 95.7% and a mesh size of 250 or higher, mixed uniformly in a certain proportion, with ethyl acetate as the solvent, thoroughly stirred and ground until the particle size and viscosity of the slurry meet the requirements for sintering. The coating method adopts either dip coating or spray coating. After coating, the specimens are vacuum sintered. Since the melting point of Ta10W is as high as 3080°C, in order to form a coating on the alloy surface through solid solution and diffusion, in addition to the coating element powder having solid solution and semi-solid solution characteristics, a higher coating sintering temperature also needs to be selected. After research, the final coating sintering process was determined to be: 1500°C~1600°C, holding for 10min~30min.
