Micropitting and microstructural evolution during gear testing -from initial cycles to failure

Abstract

To elucidate the micropitting mechanism, ground gears were tested using FZG test rig and the evolution of surface characteristics were followed closely from the initial 200 cycles to failure. Micropitting phenomenon was divided into three stages; running-in, steady progression and degradation. Micropitting was mainly associated with plastic deformation of asperities, which induced localized deformation bands and plastically deformed regions that were associated with cracks. Build-up of residual stresses occurred during running-in and this was correlated to the transformation of retained austenite. No further evolution occurred during steady progression stage and then the stresses decreased during degradation stage. Phosphorus content in the gear surface increased during steady progression stage and remained similar during degradation stage but with increased layer thickness.