Fusion bonding of solidified TiC-TiB_2 ceramic to Ti-6Al-4V alloy achieved by combustion synthesis in high-gravity field

摘要

By taking combustion synthesis in high-gravity field to prepare the solidified TiC-TiB_2 ceramic, a novel and available strategy for achieving the joint of near-full-density fine-grained TiC-TiB_2 ceramic to Ti-6Al-4V alloy in continuously-graded composition was discussed. The presence of microstructure transformation rather than a clear interface in the joint was considered a result of the achievement of the joint in multilevel and multiscale, which characterized by the size and the distribution of TiB phases. Fusion bonding and atomic interdiffusion between liquid TiC-TiB_2 and liquid Ti in thermal vacuum circumstances were considered to initiate peritectic reaction of TiB_2(s)+Ti(I)→TiB(s), direct growth of TiB solids from liquid Ti and eutectic reaction of TiB solids and liquid Ti at the final stage of joint solidification, successively, so that consumption of TiB_2 solids and the decrease of TiB crystals in size and volume both occurred, and the joint of the ceramic to Ti alloy was achieved in multilevel and multiscale. The joint in continuously graded composition and microstructure represents not only a transitional change of Vickers hardness but also the high shear strength of 450 ± 25 MPa between the solidified ceramic and Ti alloy, and shear fracture usually happen at the solidified area of HAZ (heat-affected zone) due to the presence of the coarsened α'-Ti martensitic grains and shrinkage cavities.