Effects of surface nanocrystallization on the corrosion behaviors of 316L and alloy 690

Abstract

Surface mechanical attrition treatments (SMATs) were used to prepare nanostructured surface layers on alloys used in nuclear power plant steam generators (SGs). The effects of surface nanocrystallization on alloy corrosion behavior at room temperature and at 300°C in a simulated SG environment were studied. At room temperature, the polarization curves indicated that with increasing SMAT duration, the corrosion potential of the samples shifted negatively from smaller to larger values, and alloy active dissolution rate and passive current density both increased. Nitriding treatment was used to improve the corrosion resistance. Compared with corrosion behavior observed at room temperature, corrosion resistance in the simulated SG condition was highly enhanced because the nano-sized-grain layer formed via SMAT provided a higher density of nucleation sites for the formation of a passive film and diffusion paths for Cr, leading to the rapid formation of a dense protective oxide layer.