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 10 min, reaches the maximum of 78 MPa. According to the experimental results, phase diagram and thermodynamics calculation, the interface evolution mechanism of the Al2O3/Ti–6Al–4V alloy joint was analyzed.