Study on the fretting wear performance of oxide layer and Cr coating on zirconium alloy in high-temperature water

Abstract

Grid-to-rod fretting wear is an important factor causing the fuel failure in nuclear power plants. Accident tolerant fuel (ATF) Cr coating and oxide ceramic coating have been developed to improve the fretting wear performance. In this research, two different oxide layers and Cr coating were prepared on zirconium (Zr) alloy, and the fretting wear performance were studied. The morphology, microstructure, tribo-corrosion reaction, and wear characteristics were analyzed. The oxide layer formed at high-temperature pressurized water (HTPW) has the lowest wear rate of 0.11×103 μm3/Nm due to the high hardness and compact structure, which leads to the corresponding friction pairs presenting the highest wear rate of 8.42×103 μm3/Nm. The wear depth of oxide layer formed at HTPW is about 5 times lower than that of as-received Zr alloy, and it is also less than the thickness of oxide layer. The oxide layer formed at HTPW after fretting has a larger thickness than the initial state because the plastic deformation layer caused by shear stress can quickly oxidize to zirconia in high-temperature water, and the wear rate of oxide layer is lower than the formation rate of oxide layer. The wear mechanism of two different oxide layers is delamination and abrasive wear, and that of Cr coating is abrasive wear and fatigue wear.