An Experimental and FEA approach to investigate the effect of LSP on the microstructure and corrosion resistance of Ti-17 titanium alloy.
Ti-17 is a widely used material in the aircraft and marine industry while experiences severe environmental condition in its service life. Severe breakdowns happened to the marine vessels and other materials during its service life due to the corrosion. Therefore, to strengthen its material properties against electrochemical corrosion resistance, a novel technique laser shock processing has been employed. LSP is widely used for surface modification by improving its material properties. A simultaneous FEM analysis also conducted to validate the experimental results. An Nd: YAG (Neodymium-doped yttrium aluminum garnet) laser has been equipped with a 1064 nm wavelength. Three different laser energies 8J, 9J and 10J with laser power density 11.32 GW/cm2, 12.73 GW/cm2, 14.14 GW/cm2 for 8J, 9J and 10J, respectively have been chosen. A 3 mm circular laser spot has been used with 50% overlapping rate. XRD, SEM, Vickers hardness tester, XRD sin2 (2 ) technique were used to investigate the phase transformation, microstructure and grain refinement, micro hardness and compressive residual stress (CRS), respectively. Experimental results show that, a maximum -405 MPa compressive residual stress generated in the LSPed surface which is agreed by FEM and FEM shows that the affected depth is about 1500 m from the treated surface. Microstructure test reveals the original Ti-17 consists of a typical + structure along the grain boundaries. SEM observation shows that coarse grain has been refined after the LSP treatment. Severe plastic deformation observed in the treated surface. Microhardness also improved after LSP and maximum hardness -398 HV were reported. Electrochemical test were conducted in 3.5% NaCl solution in room temperature with a three electrode system. OCP, EIS and potentiodynamic polarization study shows that corrosion resistance, corrosion current and corrosion potential improve after LSP. This research shows that the deformation induced martensites and surface roughness at higher laser power energy outweigh the beneficial grain refinement and compressive residual stress and has detrimental effect on corrosion resistance.