Microstructure evolution and mechanical properties of a lamellar near-α titanium alloy treated by laser shock peening

Laser shock peening (LSP) is a novel surface treatment technique for strengthening metal materials. The microstructural response of lamellar Ti834 alloy was investigated after treated by LSP. Micro-hardness of LSPed specimens on the surface and along the depth direction was measured. Microstructural features of plastic deformation layer induced by LSP were identified by transmission electron microscopy (TEM). Experimental results showed that the surface micro-hardness of Ti834 alloy increases gradually with increasing impact times and the peak of the micro-hardness appear in the subsurface layer of the specimen. The depth of the strengthening layer was 200 mu m and 500 mu m for the one and two impacted specimens, respectively. The compressive residual stress along the depth of the specimen increases with increasing of impact times, and the maximum compressive residual stress at the depth of 100 um from the surface of the specimen after two times impact. The microstructural evolution of Ti834 alloy with lamellar structure includes the formation of sub-grain and dislocation cell, twin-matrix (T-M) lamellae divided by the parallel MTs, MT-MT intersecting at an angle with the alpha-plates, the crossed arrangement of dislocation arrays (DAs-DAs) and the segmentation of DWs/DTs in the transverse direction.