Microstructure Evolution and Improved Surface Properties of Ti-6Al-3Nb-2Zr-1Mo Alloy by Laser Shot Peening

Abstract

In this work, the surface modification of Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy was performed by laser shock peening (LSP). The resultant microstructure, mechanical properties and corrosion properties of LSP-treated (LSPed) Ti80 were systematically investigated by 3D profiler, x-ray diffractometer (XRD), optical microscope (OM), transmission electron microscope (TEM), scanning electron microscope (SEM), microhardness tester, tensile tester and electrochemical workstation. LSP induced significant number of dislocations through plastic deformation, forming many defects such as dislocation tangles, stacking faults and deformation twins. The surface grain was severely refined due to severe plastic deformation at the surface. Microhardness improved substantially by 26.7%, compressive residual stress reached its maximum value (−307 MPa), and both microhardness and compressive residual stress presented a gradient change along depth. The tensile properties were improved by the action of work hardening, grain refinement and compressive residual stresses after LSP. The fracture changed from typical ductile to mixed ductile and brittle fracture. Grain refinement provides more nucleation sites for the formation of passivation film, while impurities are not easily segregated at grain boundaries, retarding intergranular corrosion, high-density dislocations hinder electron transfer and reduce corrosion current density, resulting in a significant improvement in the corrosion resistance of Ti80 alloy in 3.5% NaCl and 5M HCL solution.