Densification, Microstructure, and Wear Property of In Situ Titanium Nitride-Reinforced Titanium Silicide Matrix Composites Prepared by a Novel Selective Laser Melting Process

This work presents the densification behavior, microstructural features, microhardness, and wear property of in situ TiN/Ti5Si3 composite parts prepared by a novel Selective Laser Melting (SLM) process. 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 TiN reinforcing phase experienced a successive morphological change: an irregular polyangular shape-a refined near-round shape-a coarsened dendritic shape, as the applied laser energy density increased. The variations in liquid-solid wettability and intensity of Marangoni convection within laser molten pool accounted for the different growth mechanisms of TiN reinforcement. The TiN/Ti5Si3 composite parts prepared under the optimal SLM conditions had a near-full 97.7 pct theoretical density and a uniform microhardness distribution with a significantly increased average value of 1358.0HV(0.3). The dry sliding wear tests revealed that a considerably low friction coefficient of 0.19 without any apparent fluctuation and a reduced wear rate of 6.84 x 10(-5)mm(3)/Nm were achieved. The enhanced wear resistance was attributed to the formation of adherent strain-hardened tribolayer covered on the worn surface.