Corrosion resistance of laser-fabricated metal-matrix composite layer on stainless steel 316L

Laser fabrication of ceramic-reinforced metal-matrix composite (MMC) layer on stainless steel 316L was achieved by a two-step process. Ceramic powders (WC, SiC, CrB sub 2 ) and alloy-ceramic powders (Ni-WC, Co-WC, Ni-Al sub 2 O sub 3 , Ni-Cr sub 3 C sub 2 ) were preplaced on 316L specimens by pasting or flame spraying and then irradiated by a high power laser to form MMCs with low (up to 28%) and high (over 80%) volume fractions of ceramic particles. The microstructure and composition of the MMC layers were studied by optical microscopy, scanning electron microscopy, energy dispersive X-ray analysis and image analysis. The corrosion behavior of the laser-fabricated layers in 3.5% NaCl solution at 23 deg C was studied by cyclic potentiodynamic polarization technique. The pitting potential of specimens laser-modified with Co-WC and Ni-WC was shifted in the noble direction relative to 316L while there was no improvement in the corrosion resistance in the case of Ni-Al sub 2 O sub 3 and Ni-Cr sub 3 C sub 2 . For specimens modified with ceramic powders, the corrosion resistance deteriorated. The results of the present study indicated that a high volume fraction of ceramic particles in an MMC layer was unfavorable for corrosion resistance, owing to the difficulty in the formation of intact passive films