In-situ formation of novel TiC-particle-reinforced 316L stainless steel bulk-form composites by selective laser melting

Abstract

Abstract A 316L-Ti-graphite powder mixture was ball-milled for 4 h and subsequently processed by the additive manufacturing process of selective laser melting (SLM). TiC particles were formed in situ within the 316L stainless steel matrix through a laser-induced reaction via a nucleation-growth mechanism from the melt. The mechanisms underlying the formation of the TiC particles by SLM were elucidated. The effects of the applied laser energy density (η) on the densification, microstructure, and mechanical properties of the SLM-processed parts were investigated. It showed that the TiC phase was completely formed at energy densities higher than 67 J/mm3. Sub-stoichiometric TiC1−x was formed as a result of the fast cooling rate, which prevented carbon atoms from diffusing completely into the TiC crystal lattice. Scanning electron microscopy images showed that TiC particles were uniformly distributed within the 316L matrix after processing; the specimens underwent grain coarsening with the decrease in the cooling rate that is controlled by the scanning speed. The composite sample processed using low η suffer from porosity and limited densification due to poor wettability characteristics. An optimum densification of 98.88% was obtained at η of 300 J/mm3. The microhardness and wear resistance were both influenced by the densification level and grain size of the matrix. The wear tests revealed that the TiC/316L composites processed using η of 100 J/mm3 possessed the lowest wear rate of 1.31 × 10−4 mm3/N.m. The worn surface indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer.