A novel ultra-high temperature ceramic composite coating prepared by high-speed laser cladding and pack cementation on Ta–W alloys for higher plasma ablation resistance above 2300 °C

To improve the high-temperature ablation resistance properties of Ta(W) refractory alloys, a novel ultra-high-temperature ceramic (UHTC) composite coating was prepared by combining the technological advantages of high-speed laser cladding (HSLC) and pack cementation (PC). Firstly, the HSLC process was employed to fabricate a (Hf, Ta)C-Ta(W) UHTC-refractory metal composite coating that had a metallurgical bonding with the Ta(W) substrate. Then, the PC process was utilized to transform the refractory metal phase in the coating into the corresponding refractory silicide (RMSi₂) phase. Consequently, the (Hf, Ta)C-TaSi₂ UHTC composite coating was successfully prepared. This new coating was ablated at a heat flux density of 8.0 MW/m²for 300 s at a surface temperature of 2300 °C, and the coating retained its structural integrity. The linear ablation rate of the coating is -0.67 µm/s. The ablated coating exhibits three distinct oxide layers: a loose HfO₂ top layer, a dense HfO₂ middle layer, and a slightly oxidized (Hf, Ta)C<em>_x</em>O<em>_y</em> - Hf-Ta-O glassy layer. The synergistic effect of HfO₂ and Hf-Ta-O glassy oxide film endows the coating with excellent anti-ablation resistance. This innovative design of the UHTC-RMSi₂ composite coating provides robust protection to the Ta(W) substrate from ultra-high temperature ablation and mechanical scouring.