Abstract: The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology. To avoid the geometric distortion of thin-walled components caused by strengthening, the strengthening energy is limited and the ideal strengthening effect cannot be obtained. This work aims to propose a novel approach to address this issue effectively. The surface layer with high-density dislocations was obtained by a low-energy surface strengthening method (shot peening) at first. Then the surface strengthening mechanism changes from dislocation strengthening to grain boundary strengthening after electropulsing treatment (EPT). The evolution of residual stress and microstructure was analyzed using multi-scale characterization techniques. The results demonstrate that EPT followed by surface strengthening makes a remarkable 304 % increase in fatigue life of TC11 titanium alloy. The enhancement of fatigue life can be attributed to the grain refinement accompanied by the formation of nanotwins and sub-grains in the surface-strengthened layer, as well as the reduction in dislocation density within the substrate after EPT. This study demonstrates the significant potential of EPT in further enhancing the fatigue life of surface pre-strengthened thin-walled components.

Key words: Titanium alloy, Electropulsing, Surface strengthening, Fatigue performance, Dislocation density, Surface grain refinement