Effect of brazing conditions on microstructure and mechanical properties of Al₂O₃/Ti-6Al-4V alloy joints reinforced by TiB whiskers

Al₂O₃ and Ti-6Al-4V alloy were brazed with Ag-Cu-Ti+B fillers in different brazing conditions. Effects of brazing temperature, holding time and additive Ti content on joints microstructure and shear strength were investigated by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, transmission electron microscopy and shear testing. Results indicate that TiCu and Ti(Cu,Al) decrease, but Ti₂Cu and Ti₂(Cu,Al) increase in brazing seam with increasing brazing temperature, holding time and additive Ti content. Area consisting of Ti₃(Cu,Al)₃O and TiO near Al₂O₃ becomes gradually discontinuous from continuity when brazing temperature rises or holding time extends. As Ti additive content increases, TiO is absent near Al₂O₃; area consisting of only Ti₃(Cu,Al)₃O thickens. TiB whiskers are in situ synthesized by Ti and B atoms during brazing process. The brazing temperature, holding time and additive Ti content on joints microstructure influence the joints shear strength directly. The shear strength of joints, obtained at 850°C holding for 10min, reaches the maximum of 78MPa. According to the experimental results, phase diagram and thermodynamics calculation, the interface evolution mechanism of the Al₂O₃/Ti-6Al-4V alloy joint was analyzed.