Microstructure evolution and mechanical property of B₄C/Ti65 composites via laser directed energy deposition

Application of laser additive manufacture technique to fabricate the discontinuous reinforced high-temperature titanium matrix composites found its great potential in the complex components of aerospace industry. This work prepared the B₄C/Ti65 composites by laser directed energy deposition (LDED) with special attention paid to the relationship between microstructure and mechanical property of composites. The microstructure of B₄C/Ti65 composites under different laser power and B₄C content were investigated, based on which the tensile strength and ductility evolution and the underlying strengthening mechanism of the B₄C/Ti65 composites were discussed. The submicron TiBw were randomly distributed in the composites with additions of 0.1 wt% and 0.2 wt% B₄C. The TiBw and TiCp in the composites with addition of 0.3 wt% B₄C exhibited a uniform distribution rather than distributed along the prior β grain boundaries at high laser power. There existed the network structure of TiBw and TiCp in the 0.5 wt% B₄C/Ti65 composites. TiCp always adhered to TiBw, and both TiBw and TiCp acted as the nucleation sites for equiaxed α grain, which is responsible for the finer α colonies that benefit to strength with higher B₄C content. The tensile tests showed that the 0.3 wt% B₄C/Ti65 composite shows a good combination of ultimate tensile strength (1201 MPa) and elongation (5.54 %). The grain refinement strengthening played the dominant role in the strength increment of the B₄C/Ti65 composites. In addition, the formation of clustered submicron-TiBw and network structure of TiBw and TiCp in the 0.5 wt% B₄C/Ti65 composites greatly upgraded the yield strength.