Fretting wear response of a nitrided 316L SS/304L SS interface: Effect of lithium/bore liquid environment

In nuclear power plants (NPP), rod cluster control assembly (RCCA) tubes undergo impact under low-pressure contact against guides, leading to specific wear on the contact surfaces. To focus on this industrial issue, an experimental layout was designed to perform reciprocating fretting in different environments. A representative tube interface (nitrided AISI 316L)/plane (AISI 304L) was investigated in air and in a solution composed of 1000 ppm of bore and 130 ppm of lithium to be closed to a NPP primary water chemistry at atmospheric pressure and room temperature. Wear regimes were identified in terms of variation in parameters such as sliding amplitude (from +/- 40 mu m to +/- 160 mu m), normal loads (from 2 N/mm to 5 N/mm) and test duration (from 100,000 to 1.5 million cycles). Surface damage evolution was followed by 3D profilometry and several analyses (SEM, EDX, optical observation) were conducted on surfaces and cross-sections. Based on these results, fretting-wear mechanisms in the 304L SS plate and nitrided 316L SS tube were investigated. The first results in dry environment showed that, for delta(g)* <+/- 120 mu m, plane profiles had a W-shape whereas for delta(g)* >+/- 120 mu m there was a U-shape. Thus, a W-shape morphology parameter M-w was defined, taking into account the third-body wear volume. Moreover, the worn surfaces of the plane were smoother in solution, and wear was no longer detected on the tube specimens. A modified energy wear approach was then implemented to quantify reciprocating fretting wear rate according to ambient conditions. Finally, two wear mechanisms are proposed. (C) 2016 Elsevier B.V. All rights reserved.