Microstructure, mechanical and tribological properties of a Ti-5Cu alloy and a B4C/Ti-5Cu in situ composite fabricated by laser powder bed fusion

Both a novel Ti-5Cu alloy (in wt%) and a Ti-5Cu in situ composite containing 1 wt% B4C were fabricated by laser powder bed fusion, and their microstructures, mechanical and tribological properties were systematically investigated. The microstructure of the Ti-5Cu was mainly composed of α Ti laths, Ti2Cu and retained β phases, while the B4C/Ti-5Cu composite was composed of α Ti laths, Ti2Cu, TiC, TiB and TiB2 phases. Both the Cu and B4C additions promoted a transition from columnar to equiaxed grains for prior-β and α phases. The B4C/Ti-5Cu composite was found to have a higher hardness (467 HV) than the Ti-5Cu (417 HV). Further, the composite exhibits a yield strength of 1100 MPa and an ultimate tensile strength of 1250 MPa. Values which are higher than those of the Ti-5Cu that exhibits a yield strength of 750 MPa and an ultimate tensile strength of 900 MPa. However, this strength increase comes at the expense of a reduction in elongation to failure from 6.2% to 1.5%. Even though the composite is significantly stronger, the two materials exhibited very similar wear rates (ωB4C/Ti-5Cu = 4.95 × 10−4 mm3 N−1 m−1 and ω Ti-5Cu = 4.85 × 10−4 mm3 N−1 m−1).