Cavitation erosion mechanism of S31600 stainless steel laser surface-modified with unclad WC

Laser surface modification of UNS S31600 stainless steel using coarse unclad WC powder (particle size ≈60 μm) for enhancing cavitation erosion resistance was attempted. WC powder was preplaced on as-received S31600 substrate and irradiated by a high-power CW Nd:YAG laser to form a metal-matrix composite (MMC) layer on the substrate. By varying the laser fluence, MMC layers consisting of 3–28 vol.% of WC particles were formed. The microstructure, composition, and the phases present in the modified layer were studied by optical microscopy (OM), energy-dispersive spectrometry (EDS), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The cavitation erosion resistance Re in 3.5% NaCl solution was determined using an ultrasonic vibratory facility. Re was found to attain a maximum value (10.7 times that of as-received S31600) at 9 vol.% of WC. The damaged surface after the cavitation erosion test was studied by SEM to identify the damage mechanism. The variation of Re with the volume fraction of WC was explained in terms of the erosion mechanism of the matrix and the WC particles.