Fretting Wear of a 304L stainless steel in 200-bar pressurized hydrogen: A typical nodular third body structure

The aim of this study is to investigate the friction and fretting wear behavior of 304L austenitic stainless steel under high hydrogen gas pressure. Fretting tests were performed using a novel sphere-on-flat test setup in ambient air, pressurized hydrogen (200 bar), and helium (200 bar). Analysis of wear volume, frictional response, and interface morphology revealed a distinctive tribological behavior under high hydrogen pressure. At the beginning of the test, seizure phenomena occurred, leading to high coefficients of friction and severe plastic deformation inducing tribologically transformed structures (TTS). The hydrogen-embrittled ferritic TTS layer facilitated the generation of large amounts of flat wear debris. These debris particles, entrapped within the fretted interface, progressively agglomerated into nodule-like structures. Acting through a ball-bearing mechanism, these nodular debris accommodated the interface, thereby reducing both the coefficient of friction and the wear rate. Overall, while the early fretting response in hydrogen resembled that in helium, the rapid formation of a stable nodular debris layer ultimately produced friction and wear levels similar to those in air, though governed by fundamentally different mechanisms. • Fretting wear analysis of a 304L contact under pressurized hydrogen up p(H 2 )= 200 bar, • Friction behaviour involving first seizure then lower friction values thanks to nodule wear debris • Initial high wear rate due to synergic interaction between TTS process and H-embrittlement, • Nodule wear debris formed from the agglomeration of micro ferritic TTS wear debris, • Bilinear wear rate: fast wear initially (TTS debris), then slows down (Ball bearing nodule effect),