Effect of Cycle Number on the Fretting Wear Mechanism of 690TT Heat Transfer Tubes/316L Stainless Steel Caused by Fibrous Foreign Objects

Most significantly, both key parameters reach a stable state when the cycle number attains the critical value of 1×106 cycles, indicating the establishment of a steady-state wear mechanism under the specific experimental conditions. Comprehensive analysis of the wear mechanisms identifies a distinct transition throughout the testing process. The initial wear stage is primarily dominated by fatigue wear, characterized by surface cracking and material delamination.

As cycling progresses, the wear mechanism evolves into a combined action of fatigue wear and abrasive wear, with the latter confirmed by the presence of characteristic ploughing grooves and cutting marks on the worn surface. Simultaneously, material transfer becomes increasingly significant, and energy dispersive spectroscopy confirms substantial enrichment of Fe and O elements within the wear scar area. This elemental distribution pattern suggests active formation of oxide layers on the tribological surface, which is likely to significantly influence subsequent wear behavior.

This study conclusively demonstrates that under specific experimental conditions, the fretting wear process between Alloy 690TT tubes and 316L stainless steel filiform foreign objects ultimately reaches a dynamic equilibrium after undergoing different stages and sufficient cycling. These findings provide crucial experimental data and important theoretical basis for accurate safety assessment and reliable life prediction of steam generators, holding significant value for the operational safety maintenance and maintenance strategy optimization of nuclear power plants.