Fretting wear investigation of CuCrZr/Cu–OFHC contact in distilled water under contact opening sliding conditions: application to swirl-pipe divertor cooling channels of fusion reactors

In nuclear fusion devices such as WEST, ITER, and DEMO, the divertor is the main heat exhaust component, withstanding quasi-steady-state heat fluxes reaching up to 20 MW/m 2 in DEMO. Cu-OFHC swirl tapes inserted into the actively water-cooled CuCrZr pipes of the divertor improve heat-transfer efficiency. However, flow-induced vibrations may generate fretting wear at the CuCrZr/Cu-OFHC swirl-pipe interface, potentially affecting divertor lifetime. This study investigates the fretting adhesive wear behavior of CuCrZr/Cu-OFHC flat-on-flat contacts immersed in distilled water by varying several loading parameters as the number of sliding cycles, normal force, sliding amplitude, sliding frequency, contact temperature, and contact opening gap size. Adhesive wear was identified as the predominant damage mechanism under all tested conditions and was mainly activated during the running-in period through direct metal–metal interactions between the copper-based counterbodies. The wear volume remained nearly constant with increasing test duration, temperature, and sliding frequency, whereas it increased with the normal force and the sliding amplitude and decreased with increasing contact opening gap size. These trends demonstrate that adhesive wear is mainly governed by the dissipated friction energy density at the interface rather than by the classical Archard p·v factor. A power-law formulation was established between the mean wear depth and the friction energy density. These results provide a quantitative basis for assessing fretting wear damage and supporting fretting lifetime prediction of swirl-pipe contacts in water-cooled fusion divertor components.