Design of High Emissivity Coatings for Hypersonic Applications Using Suspension Plasma Spray

Hypersonic vehicles require sharp-featured nose tips and wing leading edges to reduce aerodynamic drag. However, the geometry of these edges increases the convective heat flow to the surface, ultimately increasing the surface temperature of the component to >1500°C. Ultra-high temperature ceramics (UHTCs) such as ZrB₂ with SiC addition is often propose for use as protection for structural systems in high temperature oxidative environments.  In this study, rare earth oxides are added to ZrB₂-SiC suspension plasma spray coatings to improve their high temperature properties by increasing emissivity. The surface temperature of the coating will be kept at a lower temperature by increasing its radiation heat transfer. During plasma spray process, neodymium and samarium nitride reacts in the plume to form ZrB₂-20vol%SiC-RE₂O₃ (RE=Sm, Nd) coatings. These 300μm thick coatings have a columnar structure and a relative density of approximately 60%. X-ray diffraction data suggests that the dopants have been incorporated into the coatings. Thermogravimetric analysis (TGA) also shows that doped coatings undergo less oxidation compared to the baseline coating up to 1300°C.