Laser peening improved fatigue life and strength of single crystal CMSX-4 after corrosive and high temperature exposure

^{This study investigated the stress relaxation and fatigue life and strength of laser peened single crystal nickel superalloy (CMSX-4) specimens following sulfate corrosion and 300 hours air oven exposure at 700C. Fatigue testing compared un-peened, shot peened and laser peened specimens. The laser peened specimens were treated by large energy/ large spot peening and several specimens by a new cyclic laser peening plus thermal microstructure engineering (LP+TME) process. Stress measurements by slitting crack-compliance showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Tests of five non-laser peened specimens all failed in the low cycle fatigue regime at 27 k-cycles or less, whereas three identically tested laser peened specimens all achieved greater than 2-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests showed fatigue strength improvement of 2:1 by laser peening.}

Keywords: laser peening, fatigue strength, stress relaxation, corrosion, Ni-based superalloy