Property and thermostablity study on TC6 titanium alloy nanostructure processed by LSP

TC6 titanium alloy samples are processed by laser shock peening (LSP). Then, some samples are vacuum annealed at 623 K for 10 h for the study on the thermostablity of the nanostructure produced by LSP. The characteristics of the strengthened layer and nanostructure are studied by atomic force microscopy(AFM), scanning electron microscope(SEM), electron backscatter diffraction(EBSD), X-ray diffraction(XRD), and transmission electron microscopy(TEM) appliances, meanwhile the enhanced microhardness is tested at cross section. AFM of the processed surface indicates that the deformation is approximately uniform, and LSP slightly increases the roughness. SEM and EBSD of the strengthened cross section show that α phases are compressed to strip-shaped, a proportion of α and β phases is shattered to smaller phases from surface to 200 μm in depth. The surface XRD shows that although there is no new produced phase during LSP, the grain size refinement and the introduction of lattice micro-strains lead to the broadened peak. The TEM photographs and diffraction patterns indicate that the shock wave provides high strain rate deformation and leads to the formation of nanocrystal. Compared with the samples before annealing, the dislocation density is lower and the grain-boundary is more distinct in the annealed samples, but the nanocrystal size does not grow bigger after annealing. The microhardness measurement indicates that LSP improves the microhardness of TC6 for about 12.2% on the surface, and the layer affected by LSP is about 500 μm in depth. The microhardness after annealing is 10 HV _0.5 lower, but the affected depth does not change. The thermostable study shows that the strengthened layer of TC6 processed by LSP is stable at 623 K. The strengthened thermostable layer can significantly improve the fatigue resistance, wear resistance and stress corrosion resistance of the titanium alloy. The study results break the USA standard AMS2546 that titanium parts after LSP are subjected in subsequent processing within 589 K.