Effects of SiC content on phase evolution and corrosion behavior of SiC-reinforced 316L stainless steel matrix composites by laser melting deposition

SiC dispersed (4, 8, 12 and 16 wt%) 316L stainless steel metal matrix composites (MMCs) have been prepared by laser melting deposition (LMD). The constituent phases, microstructure, microhardness and electrochemical properties of the MMCs were investigated as a function of SiC content. Experimental results showed that constituent phases of the MMCs evolved from single gamma-(FeCrNi) phase with fcc structure for 4 wt% SiC dispersed MMC to gamma-(FeCrNi) + alpha-(FeCrNi) + SiC phases for the 8,12 and 16 wt% SiC dispersed MMCs. The presence of alpha-(FeCrNi) phase was due to the tensile stress resulting from the different coefficient of thermal expansion between SiC ceramic reinforcement and the gamma-(FeCrNi) matrix in the MMCs. In addition, iron silicides (Fe3Si and FeSi) appeared in 16 wt% SiC dispersed MMC. The microstructure was dense, uniform and the addition of SiC obviously refined the solidification microstructure of the MMCs. In the 16 wt% SiC dispersed MMCs, a micro-crack can be dearly observed. The microhardness of MMCs increased obviously from 362 HV to 974 HV with the addition of SiC. Accompanying the increase in hardness, the corrosion current density increased and the charge transfer resistance decreased, and the corrosion resistance of 4 and 8 wt% SiC dispersed MMCs was superior compared to 12 and 16 wt% SiC dispersed MMCs in 3.5 wt% NaCl solution.