In situ synthesis of TiB whisker reinforcements in the joints of Al2O3/TC4 during brazing

Abstract

Al2O3 ceramic has been successfully joined to Ti–6Al–4V alloy with Ag–Cu–Ti–B mixed powder. The TiB whiskers in the brazing layer were in situ synthesized during brazing. The effects of B content in reactant on the phase composition, microstructure and shear strength of the joints were investigated using SEM, EDS, and shear test. Results indicate that B content in the filler has a great impact upon the microstructure of the joints via exerting an influence on the volume fraction of in situ synthesized TiB whiskers. When the TiB content is 40vol.%, the shear strength reaches the maximum value of 77.9MPa. The higher content of TiB (≥40vol.%) depresses the shear strength of the joints due to the interfacial thermal stress cannot be relaxed. Reaction phases (Ti3Cu2AlO, Ti2Cu, Ti2(Cu, Al), Ti(Cu, Al) and Ti3Al) appear in the joint, moreover, as the volume fraction of TiB increase, Ag (s.s) and Ti(Cu, Al) distribute more uniform and fine in the brazing layer, as well as TiB whiskers mainly distribute in them. Eventually, Ti3Cu2AlO, TiB and TiB2 firstly generate based on the thermodynamic analysis, and in excessive Ti circumstances, TiB whiskers remain in the brazing alloy.