TiBw reinforced titanium matrix composites fabricated by selective laser melting: Influence of energy density on microstructure and tribological performance

For the application of high-performance titanium alloy parts in the additive manufacturing of aerospace, automotive and other fields, titanium matrix composites reinforced by TiBw were fabricated using selective laser melting technology. The influence of different energy densities on the microstructure, microhardness and tribological performance of TiBw/Ti6Al4V composite were studied, and the formation and evolution mechanism of the unique microstructure was analyzed. It is found that the TiBw/Ti6Al4V composite fabricated by SLM is mainly composed of a fine & alpha;e-Ti matrix, nano-scale TiBw produced by the in-situ reaction and residual TiB2 particles. The size, morphology and distribution of TiBw and its aggregated network structure are related to laser energy density. As the energy density increases, the morphology of TiBw evolves from tiny acicular to thick rodlike or plate-like. Additionally, the network chain composed of TiBw gradually expands or even breaks. Compared with Ti6Al4V alloy processed by SLM and traditional casting, the microhardness and wear resistance of TiBw/Ti6Al4V composites fabricated under various energy densities are significantly improved, and the friction process is affected by the abrasive wear, adhesive wear, and oxidation wear mechanisms. The good tribological performance is attributed to the fine-grain strengthening of Ti matrix and the second-phase strengthening effect caused by the network structure of TiBw.