Microstructure evolution during cycling in vacuum and air environments: Correlation with mechanical behaviour

An experimental study was performed on polycrystalline copper at different plastic strain amplitudes in air and vacuum to quantitatively assess the link between the microstructure evolution and the mechanical behaviour. Fatigue life extension due to vacuum environment allowed the observation of a second hardening stage at low plastic amplitude. This finding, in contrast to the stabilisation regime observed in air made it possible to state that the dislocation structure continues to evolve beyond the failure in air. In addition, the dislocation microstructure was found to evolve in a sequence of veins, walls-channels and elongated cells to attain an equiaxed cell arrangement with continued fatigue cycling. Moreover, the quasi-stabilised regime took place with different dislocation structures according to the plastic strain level.