In Situ Ti–Si Intermetallic-Based Composites by Selective Laser Melting (SLM) Additive Manufacturing (AM): Designed Materials and Laser-Tailored In Situ Formation

Abstract

Based on an integrated processing method of “Designed materials,” “Laser-induced in situ reaction,” and “Tailored mechanical performance,” theTiC/Ti5Si3 and TiN/Ti5Si3 composite parts were produced by selective laser melting (SLM) additive manufacturing (AM) process, starting from the high-energy ball-milled SiC/Ti and Si3N4/Ti powder systems. The influence of the applied laser energy density on the densification behavior, microstructural features, microhardness, and wear property of in situ Ti5Si3-based composites was studied. The occurrence of balling phenomenon at a low-laser energy density combined with a high-scan speed and the formation of thermal cracks at an excessive laser energy input generally decreased densification rate. The in situ formed TiC and TiN reinforcing phases experienced a successive morphological change as the SLM processing conditions varied. The underlying metallurgical mechanisms accounted for the different growth mechanisms of TiC and TiN reinforcement during SLM process were disclosed. The in situ TiC/Ti5Si3 and TiN/Ti5Si3 composite parts prepared under the optimal SLM conditions had a near-full density, a significantly elevated microhardness (> 980 HV), a considerably low coefficient of friction (< 0.2), and a reduced wear rate. The enhanced wear resistance was attributed to the formation of adherent strain-hardened tribolayer covered on the worn surface.