Zirconium diboride and hafnium diboride ceramics have been used in heat shields. The new development is an 'alloy' of many different metallic diborides which is

Zirconium diboride and hafnium diboride ceramics have been used in heat shields. The new development is an 'alloy' of many different metallic diborides which is glassy (high-entropy) instead of crystalline, and is less brittle. https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic https://en.wikipedia.org/wiki/Ultra-high_temperature_ceramic