Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology(especially the shape) and, consequently, density and compression properties of in situ Ti–Ti B composite materials produced by selective laser melting(SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium(CP-Ti) and 5wt% titanium diboride(TiB 2) powders and subsequently milled for two different times(i.e. 2 h and 4 h).The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively.Subsequently, the resultant Ti–5 wt% TiB 2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti–Ti B composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB 2during SLM. The Ti–Ti B composite samples prepared from 2 h and 4 h milled Ti–TiB 2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those(883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB 2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density(i.e. increasing porosity level) of the Ti–Ti B composite materials and their mechanical properties.