Tribolayer evolution and subsurface microstructural transformation in Cr-coated Zr alloy claddings under fretting corrosion in simulated PWR primary water

The fretting corrosion of Cr-coated Zr alloy cladding in simulated pressurized water reactor (PWR) primary water (315 °C, 15 MPa, LiOH+H₃BO₃ chemistry) was systematically investigated, with a particular focus on the effects of displacement amplitude and normal load. Using a custom high-temperature and high-pressure autoclave system, the fretting corrosion response of Cr-coated cladding against Inconel 718 was evaluated through multiscale characterization. Results revealed that increasing displacement amplitude markedly intensified wear damage—evidenced by greater wear depth, volume, and Archard coefficient—and induced a transition from adhesive to abrasive-fatigue wear mechanisms. This evolution was accompanied by thinning or loss of the protective third body layer (TBL), suppression or exfoliation of the tribologically transformed structure (TTS), and pronounced plastic deformation layer (PDL) in the underlying Cr coating. Conversely, increasing normal load enhanced TBL compaction, reduced TTS cracking, and mitigated subsurface damage. These findings establish a mechanistic framework for understanding and optimizing the fretting corrosion resistance of Cr-coated Zr claddings under PWR conditions.