A study on the effects of laser shock peening on the microstructure and substructure of Ti-6Al-4V manufactured by Selective Laser Melting

Ti-6Al-4V was fabricated by powder-bed fusion using different laser scanning strategies. The microstructure and deformation properties were investigated in the as-built condition, and also after the material had been subjected to a laser-shock-peening (LSP) treatment. The microstructure in each condition was surveyed using 3D optical microscopy, EBSD, and TEM. The post-manufacture residual stresses were determined. The results indicate a correlation between the residual stresses and the substructures observed in TEM: tensile residual stresses from the surface down to 1 mm depth were observed in the as-built material, corresponding to extensive deformation through twinning of the {1012} type and wavy slip structures; while after LSP the alloy showed a variety of dislocation arrangements, especially planar and in significantly higher density, along with {1122} twins and with the presence of compressive residual stresses. The findings indicate that the deformation capability is mecha-nistically aided by the peening process, which effectively promotes the replacement of tensile residual stresses by compressive ones, offering routes for potentially improving the mechanical properties of the additively manu-factured Ti-6Al-4V, as well as its usability.