ZrB₂–SiC/Ti6Al4V joints: wettability studies using Ag- and Cu-based braze alloys

In this paper, a study is presented on the wettability of ZrB₂ ceramics (pure ZrB₂ and ZrB₂–SiC composite) and of the Ti6Al4V alloy by pure Cu and Ag and their alloys with Ti to be used in subsequent brazing processes. Wettability tests aimed at elucidating the interfacial interactions and the role of active metal additions (i.e. Ti) in the brazing procedure, performed in a temperature range between 950 and 1150 °C, showed that Cu wets pure ZrB₂ quite well (contact angle θ = 70°), while Ag does not. The composite was wetted in a similar way by Cu, while for Ag a θ = 97° was found. The addition of Ti improved the wetting (θ between ~0° and 20°) and segregation at the metal–ceramic interface occurred. As expected, both Cu(Ti) and Ag(Ti) wetted the Ti6Al4V alloy very well. In particular, it was shown that Cu can already produce a liquid phase at 950 °C with partial dissolution of the solid phase. These results are discussed in terms of interfacial reactions and taking into account the sintering aids used for the ceramic body. This study is aimed at defining a brazing process that leads to reliable metal–ceramic joints as a result of chemical interactions of the liquid phase with and diffusion into the adjoining solids. Exploratory joining tests were performed that showed, by means of shear tests coupled with microstructural and microchemical description of the interfaces, the possibility to design sound ZrB₂–SiC/Ti6Al4V joints.