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. Metal–ceramic powders (Ni–WC, Co–WC, Ni–Al2O3, Ni–Cr3C2) and ceramic powders (WC, SiC, CrB2) were preplaced on 316L specimens by flame spraying and pasting, respectively. The preplaced coatings were 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, x-ray diffractometry, and image analysis. The corrosion behavior of the laser-fabricated layers in 3.5% NaCl solution at 23 °C was studied by the cyclic potentiodynamic polarization technique. The corrosion resistance of the laser-surfaced specimens varied depending on the type and volume fraction of the reinforcement incorporated. In general, the corrosion potential shifted in the noble direction relative to 316L, but the pitting corrosion resistance deteriorated. Moreover, the results of the present study indicate that a high volume fraction of ceramic particles in an MMC layer was unfavorable for pitting corrosion resistance due to the difficulty in the formation of intact passive films and the presence of vulnerable spots at the ceramic/matrix interface.