Evolution of fretting wear characteristics of Cr-coated cladding under high-temperature pressurized water environment

The Cr (chromium) based coating is the most simple, studied, and promising coating for the accident-tolerant fuel cladding of pressurized water reactors. In this work, special tangential fretting wear equipment in high-temperature pressurized water was used to carry out experimental research. The influence of cycles on the fretting wear of Cr-coated cladding under high-temperature and high-pressure water environment was investigated, and the evolution characteristic of the coating during the wear process was revealed. The results show that with the increase in cycles, the main wear mechanism of Cr cladding changes from adhesive wear to fatigue wear, and finally to abrasive wear and delamination. Crack caused by fatigue wear during fretting wear was the main factor leading to the failure of the coating. In addition, wear debris accumulated on the surface of the Cr coating during wear and formed a dense friction oxidative layer (glaze layer), so that the Cr coating can maintain a complete structure in the early stage of fretting wear. The shear stress generated by the friction process will accelerate the material removal, and the existence of a friction oxidative layer can play a certain role in lubrication. The two were in a competitive relationship and finally formed a wear cycle mechanism of wear, oxidation, and re-wear.