Stratified surface layers affecting crack propagation in wheel-rail contacts

To withstand increasing mechanical and thermal loads affecting rails and wheels due to intensified rail transportation, comprehensive knowledge of evolving near-surface microstructures in the wheel-rail contact is vital. Stratified surface layers (SSLs) observed in the field gained attention recently. This study extensively investigates a textbook example of SSL detected on a rail wheel. Results show crack initiation in the white etching layer (WEL) with propagation into the underlying brown etching layer (BEL) with changing crack growth direction. Within the BEL, a microstructural gradient is observed with decreasing grain size and increasing hardness with increasing distance from surface. This work provides new insights in the microstructural and micro-mechanical characteristics of SSLs and improves the knowledge of evolving stratification in wheel-rail contacts.