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.