High speed laser cladding as a new approach to prepare ultra-high temperature ceramic coatings

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.