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). First, the HSLC process was employed to fabricate a (Hf,Ta)C–Ta(W) UHTC–refractory metal composite coating that had 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/m² for 300 s at a surface temperature of 2300 °C, and the structural integrity of the coating was retained. 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_xO_y–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.

Ultra-high temperature ceramic (UHTC) coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation. This study provides a new approach to fabricate UHTC coatings with high speed laser cladding (HSLC) technology, and places more emphasis on investigating the formation mechanism, phase compositions, and mechanical properties of HSLC-UHTC coatings. Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed. The coating is mainly composed of (Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W) metal solid solution phase. At a relatively high powder feeding rate, the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to ~50 μm is successfully fabricated. As for the mechanical properties of the HSLC coatings, the fracture toughness of the coating decreases with the increase of powder feeding rate. The increase of carbide solid solution phase can significantly improve the high temperature microhardness (552.7±1.8 HV_0.5@1000 ℃). The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer, which is a very promising candidate scheme for thermal protection coating.

Ultrahigh-temperature ceramics (UHTCs) are a kind of thermal protecting material used in the extreme thermal environment due to their excellent temperature resistance. However, their intrinsic brittleness and poor thermal shock resistance restrict the engineering applications. Graphene as a two-dimensional (2D) nano-material where carbon atoms are arranged in a honeycomb structure has superior mechanical, electrical and thermal properties. It is often used as an additive phase to modify the ceramic matrix, and is considered as an ideal toughening material in ceramic composites to realize the functionalization and structuralization of composites. This review represented recent research work on the preparation process, bionic construction method, microstructure and macro properties of graphene/UHTCs. The toughening effects and mechanism, thermal properties, thermal shock resistance and oxidation resistance of UHTCs doped with graphene were discussed. In addition, some challenges and future development of this field were also put forwarded.