Improvement of fatigue life of Ti-6Al-4V alloy by laser shock peening

The aim of this paper was to address the effects of multiple laser peening and laser peening intensity used in laser shock peening (LSP) on the residual stress, micro-hardness and three-point bending fatigue performance of Ti-6Al-4V alloy. The multiple laser peening was accomplished by using the successive laser shocks at the same spot and the laser peening intensity was changed through changing the number of overlapped laser spots. The microstructure, which was characterized by highly tangled and dense dislocation arrangements due to high strain rate, can be found near the surface of the laser-peened specimen. By comparing with the as-received specimen, high micro-hardness and compressive residual stress were introduced at the surface of the laser-peened specimen. With increasing the number of overlapped laser spots, the fatigue life of the laser-peened specimen increased, reached a local maximum and then decreased. The specimen treated by using three overlapped laser spots exhibited the highest fatigue life. When the number of overlapped laser spots was kept to be three, the LSP treatments with one single laser shock and two successive laser shocks respectively provided a 22.2% and 41.7% increase in the fatigue strength as compared with the as-received specimens.