Fatigue Performance Improvement by Dynamic Strain Aging and Dynamic Precipitation in Warm Laser Shock Peening of AISI 4140 Steel

Warm laser shock peening (WLSP) integrates the advantages of laser shock peening and thermal-mechanical treatment (TMT) to improve material fatigue performance. Compared to traditional laser shock peening (LSP), warm laser shock peening, i.e. LSP at elevated temperature, leads to better performance in many aspects. WLSP can induce nanoscale precipitations by dynamic precipitation and high density dislocation by dynamic strain aging (DSA), resulting in higher surface strength, which is beneficial for fatigue life improvement. Due to pinning of dislocation structure by nanoscale precipitates, and the pinning of dislocation structure by Cottrell atmosphere, or the DSA effect, stability of the dislocation arrangement is significantly increased and the residual stress stability improved. In this study, AISI 4140 steel is used to evaluate WLSP process. It is concluded that the higher residual stress stability and higher surface strength caused by dynamic precipitation and DSA in WLSP leads to fatigue life improvement.