Hydrogen effect on the cavitation erosion resistance of AISI 316L stainless steel laser surface-modified with NiTi

Abstract

AISI 316L stainless steel was laser surface-modified with NiTi for improving cavitation erosion resistance as reported in a previous study. The present study aimed at investigating the effect of hydrogen charging on the cavitation erosion resistance of the NiTi-modified layer, in comparison with 316L substrate and bulk NiTi plate. To compare the hydrogen effect, the three types of samples were subjected to the same electrolytic charging intensity. The change in surface morphology and in the phases present was studied by scanning-electron microscopy and X-ray diffractometry. The indentation properties were studied using Vickers microhardness test and nanoindentation test. Cavitation erosion test indicated that hydrogenation resulted in different degrees of decrease in erosion resistance in all the three types of samples, which could be attributed to different mechanisms. For 316L, the hydrogen effect was mild, congruent with the small change in indentation properties. For NiTi-modified 316L, the decrease in resistance was due to a drop in hardness and elasticity, while for bulk NiTi, the decrease was mainly attributable to the formation of hydrides leading to the presence of surface cracks.