Selective laser melting of in situ titanium-titanium boride composites: Processing, microstructure and mechanical properties

This study presents results of selective laser melting (SLM) processing of in situ Ti-TiB composites from optimally milled Ti-TiB2 powder. Optimized tuning of the SLM manufacturing parameters was applied to obtain almost fully dense (>99.5%) Ti-TiB composites. X-ray diffraction and electron diffraction patterns as well as microstructural investigations indicate a chemical reaction during SLM in which irregular-shape titanium diboride (TiB2) particles react with pure Ti to form needle-shape titanium monoboride (TiB) particles. Transmission electron microscopy investigations reveal that Ti grains are refined significantly due to the existence of B. The microhardness, yield stress and compressive strength of the SLM-produced Ti-TiB composites increase to 402 Hv, 1103 MPa and 1421 MPa, respectively, compared to 261 Hv, 560 MPa and 1136 MPa, respectively, for the SLM-produced commercially pure Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB particles and refinement of Ti grains. Fractography analyses show that a mixture of splitting/shearing and smooth/rough zones covers the fracture surfaces of failed composite samples after compression testing. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.