Metal-Ceramic Interactions in Brazing Ultra High Temperature Diboride Ceramics

In this chapter we reported the most peculiar issues related to the metal-ceramic interactions encountered when joining transition metal diborides of the 4th group (TiB2, ZrB2 and HfB2) which belong to the broader family of ultra high temperature ceramics. The most peculiar characteristics of these materials were recalled especially in relation to environmental conditions characterized by extremely high temperatures, mechanical loads and oxidation phenomena. Basics about high temperature wetting of liquid metals on ceramics and their importance in view of brazing processes for ceramics were presented. Recent data about the wetting of liquid metals and alloys on TiB2, ZrB2 and HfB2 and their composites has been collected and discussed. Contact angle data, information on interfacial reactivity and final microstructures, and their interpretation through modelling (e.g. by CALPHAD) constitute the basis for the correct design of joining processes in view of high demanding applications.