Fretting wear-induced sudden loss of corrosion resistance in a corrosion-resistant Ni-based alloy

The fretting corrosion testing of A690 with a sliding amplitude of 100 μm and a normal force of 20 N was conducted in a manually designed equipment with a tube-on-plate contact configuration exposed to simulated pressurized water reactor (PWR) secondary water. While A690 exhibits superior corrosion resistance, the fretting wear results in a two orders of magnitude faster oxidation rate at the contacting surface. A detailed characterization reveals that the fretting wear-induced dynamic stress/strain does not only constantly break the integrity of the oxide scale but also accelerate the consumption of Cr in the near-surface metal matrix. The degradation of corrosion resistance of A690 under fretting wear can be mainly attributed to 1) the decrease of oxide scale thickness; 2) the introduction of nanocavities and nano-cracks at the grain boundaries of the oxide scale; 3) the formation of a nano-grained Cr-depleted matrix zone under the oxide scale. These findings suggest that, for the structural alloys serviced at elevated temperatures, even a small amplitude motion with low normal stress against their contacting surface could significantly deteriorate their corrosion resistance. Hence, the service lifetime of the structural alloys needs to be reconsidered once friction is existing.