Microstructural evolution and mechanical properties of duplex-phase Ti6242 alloy treated by laser shock peening

The effects of laser shock peening (LSP) on the microstructural evolution and mechanical properties of the Ti6242 alloy, including the residual stress, surface roughness, Vickers microhardness, tensile mechanical response, and high-cycle fatigue properties, were studied. The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material. The maximum surface residual compressive stress was -661 MPa, and the compressive-stress-affected depth was greater than 1000 mu m. The roughness and Vickers micro-hardness increased with the number of shocks, and the maximum hardness-affected depth was about 700 mu m after three LSP treatments. LSP enhanced the fraction of low-angle grain boundaries, changed the grain preferred orientations, and notably increased the pole density of alpha phase on the near surface from 2.41 to 3.46. The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening, while the LSP had a limited effect on the tensile properties. The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20% compared with that of the untreated sample, which was caused by the suppression of the initiation and propagation of fatigue cracks.