Direct evidence of melting and decomposition of TiC particles in laser powder bed fusion processed 316L-TiC composite

Abstract

Recent advancements have shown the effectiveness of strengthening 316L with TiC particles addition through the laser powder bed fusion (LPBF) process. However, the question remains whether TiC undergoes decomposition into Ti and C atoms, primarily because of the challenges associated with measuring C at low concentrations. In this study, we employed atom probe tomography (APT) to provide evidence of decomposition by observing the presence of Ti and C atoms in the 316L matrix. The fast cooling rate of the LPBF process results in the supersaturation of Ti and C in the 316L matrix. Adding 3 wt% TiC particles increased the yield strength of LPBF-processed 316L from 599 MPa to 832 MPa. The subsequent annealing treatment resulted in the formation of more TiC nanoparticles as a result of precipitation from the supersaturated Ti and C in the 316L matrix. Consequently, the yield strength was further enhanced to 959 MPa after annealing at 700 °C for 1 h. This study marks the first direct demonstration of the decomposition of TiC in metal matrix composites.