In-Situ Eutectic Ultra-High-Temperature Ceramic Coatings with Dispersed Rhenium Intermetallics for Reusable Thermal Protection Systems

Abstract

Reusable launch vehicles and hypersonic re-entry vehicles experience surface temperatures that routinely exceed 2000 °C on leading edges and nose tips. Conventional ultra-high-temperature ceramic (UHTC) coatings based on hafnium or zirconium diboride offer high melting points but remain vulnerable to thermal-shock cracking and delamination caused by coefficient-of-thermal-expansion mismatch with the underlying composite substrate. This paper describes a coating architecture that forms its final microstructure in situ during the first high-temperature exposure. A precursor layer of HfB₂ or ZrB₂, SiC and finely dispersed rhenium-based intermetallic particles is applied to a carbon-carbon or ceramic-matrix-composite substrate. When the surface temperature reaches approximately 1800–1950 °C the constituents undergo a localized eutectic reaction that produces an interwoven multiphase network whose expansion behaviour more closely matches the substrate. The rhenium-rich particles act as crack-arrestors at grain boundaries. Simultaneously, controlled oxidation of the matrix generates a viscous hafnium-borosilicate glass that flows into surface microcracks and remains adherent under hypersonic shear. The result is a self-healing, thermally compliant coating intended for repeated re-entry cycles.