On high temperature fretting in liquid lead

The increasing interest in liquid metal cooled nuclear reactors provides technical and scientific challenges, such as the understanding, prevention, and prediction of the degradation of materials in liquid lead. This work examines fretting wear, occurring between the spacer wire wrapped around fuel tubes and between the steam generator tubes and their supports. Studies of fretting in liquid lead often focus on the corrosive effects of lead and employ varying test methods. Comparing results from specially built equipment and widely used lab-scale test rigs is challenging because the rigs operate over different load ranges and in different environmental conditions. Publications on the topic lack detailed descriptions of wear mechanisms and friction data. At the same time, both short- and long-duration experiments under conditions relevant to nuclear reactor operation are necessary. This work aims to develop a simplified test methodology for new candidate materials intended for liquid-metal environments and to perform fretting tests on selected materials to understand the dominant wear mechanisms. The modified oscillating friction and wear tester and the developed methodology were shown to be suitable for investigating fretting in liquid lead. The waviness of the test specimen surfaces significantly influences friction and wear behavior. Lower surface roughness showed superior fretting performance for self-mated Fe-10Cr-4Al, resulting in reduced local contact pressures that limit plastic deformation and material removal. The findings emphasize the importance of surface topography control in mitigating fretting damage in components. The tribopair with one surface laser-clad with Fe-10Cr-4Al exhibited the lowest wear rate among all tested Fe-10Cr-4Al tribopairs. This is attributed to the difference in hardness between the specimens, which promotes distributed plastic deformation and the formation of a more uniform debris layer. Fretting tests of self-mated Fe-10Cr-4Al alloy were performed using the modified friction and wear tester and a specially built equipment. After tests with an increasing number of cycles, similar wear mechanisms and wear depths were observed at both facilities. A reduced lubricating effect from saturated lead and its limited availability at the contact were shown to be the main damage-accelerating factors.