Wetting of Group IV diborides by liquid metals

Abstract

The possibility to exploit the peculiar characteristics of transition elements diboride ceramics—a class of promising materials for high temperature and highly aggressive applications—often depends to a great extent on the ability to join the ceramic parts one to the other or to special metallic alloys. Therefore, the knowledge of wettability, interfacial tensions and interfacial reactions is mandatory to optimise the joining processes. Data on the wettability and the interfacial features of different metal–ceramic systems, particularly of (Ti,Zr,Hf)B2 in contact with liquid non-reactive metals Cu, Ag, Au and their alloys, are reported and critically discussed, beginning with the pioneering work made in European eastern countries in the 70s up to the most recent published and new data. Moreover, interfacial energetics at the atomistic level is being increasingly investigated by means of sophisticated modelling techniques such as pseudopotential-based Density Functional Theory (DFT). These approaches will be presented, referred to non-oxide metal–ceramic systems. Given the complexity of ab initio calculations, the study is limited to the ideal work of separation, i.e. with plastic and diffusional degrees of freedom suppressed. Nevertheless, it is shown that the results on the specific transition borides-molten metal systems can be used to interpret the wetting behaviour and the adsorption/reaction interfacial phenomena involved.