Abstract: 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-TiB 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 5 wt% titanium diboride (TiB₂) powders and subsequently milled for two different times (i.e. 2h and 4h). The milled powder mixtures after 2h and 4h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB₂ powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB 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 TiB₂ during SLM. The Ti-TiB composite samples prepared from 2h and 4h milled Ti-TiB₂ 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 1421MPa and 17.8%, respectively, which are superior to those (883MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB₂ 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-TiB composite materials and their mechanical properties.

Key words: Selective laser melting, In situ Ti-TiB composite, Powder shape, Density, Mechanical properties