Fretting wear of a nitrided 316L/304L contact subject to in-phase normal force fluctuation in dry and lithium-boron solution: An RP-friction energy wear approach

Abstract

In nuclear power plants, tubes of the rod cluster control assemblies undergo impacts at low contact pressures against guides, causing specific wear on the contact surfaces. The present study investigates fretting wear behavior under variable loading, using an original double-actuator fretting wear system which allows independent control of tangential sliding and normal force fluctuation. Using this test system the fretting wear response of a nitrided 316L SS cylinder fretted against a 304L SS plate in air and in a lithium-boron solution is investigated.The effect of normal force fluctuations quantified using the RP=Pmin/Pmax ratio was investigated keeping constant the tangential sliding amplitude. Surface damage evolution was followed by 3D profilometry and several analyses were conducted on specimen surface and cross-sections (SEM, EDX). To quantify the wear volume extension, an RP-weight friction-energy-wear parameter (i.e.,RPη×ΣEd) is introduced. This new loading parameter allows us to take into account both friction work and normal force fluctuation.For a dry interface the η exponent was found to be very small (0.15) suggesting that the wear volume is directly related to the friction energy dissipated in the interface. In contrast, in lithium-boron solution the best fitting was achieved with ηw=−0.9 which implies an energy wear rate nearly inversely proportional to RP. The larger the normal force fluctuation (i.e., the smaller RP) the larger the contribution of tribocorrosion and the faster the surface wear. Besides, unexpected erosion-corrosion wear phenomena were identified at the inlets of the contact. These different wear mechanisms are discussed and quantified.