Evolution of Fretting-Induced Cracks and Delamination Wear on Alloy 690 Steam Generator Tubes During Mixed Fretting Regime in Air at Room Temperature

Abstract

The occurrence of fretting-induced cracks and delamination wear processes in a mixed fretting regime on Alloy 690 steam generator tubes against 304L stainless steel pads was analyzed. Fretting tests in 90° cross-cylinder configuration were performed in air at room temperature. Changes in the contact conditions were evaluated using the energy ratio and the sliding ratio criteria. Damage was characterized using light microscopy, scanning electron microscopy, and optical profilometry. Vickers microindentation was applied to characterize the initial plastic deformation process. It was found that during the initial 1 × 10³ cycles, plastic deformation constitutes the main damage mechanism. Thereafter, between 1 × 10³ and 1 × 10⁴ cycles, cracks nucleation and propagation accompanied by negligible wear were detected. Beyond 1 × 10⁴ cycles, the dominant main damage mechanism consists of delamination wear assisted by cracks coalescence, and a change from a U-shaped to a W-shaped scar profile was observed in correspondence with the appearance of the delamination wear process.

Keywords:

• Fretting
• steam generator tubes
• alloy 690
• delamination wear
• SEM

Acknowledgements

The assistance of Fernando Becker in the preparation of the metallography and the support of the Abaqus Modeling of the Department of Mechanical Engineering of the CAREM Project are gratefully acknowledged. We also appreciate the support of CNEA, CONICET, and Instituto Balseiro.

Disclosure Statement

No potential conflict of interest was reported by the author(s).