Residual stress reduction in Ti-6Al-4V parts fabricated by laser-foil-printing process

In this study, the effects of two scan strategies, line pattern scanning (LPS) and spot pattern scanning (SPS), on alleviating the accumulation of residual stress were investigated for the fabrication of Ti-6Al-4V (Ti64) parts using a laser-foil-printing (LFP) additive manufacturing process. The residual stresses in the parts prepared using SPS in LFP were substantially reduced (by 56 %) from 1161.8 to 530 MPa compared to the use of LPS alone, as determined by X-ray diffractometry (XRD). Three-dimensionally coupled thermal–mechanical models were developed to combine the practical residual stress, melt pool, and deformation of Ti64 parts in LFP using the finite-element method (FEM), which exhibited a minor deviation of less than 11.6 % between the experimental and simulated results. Additionally, cross-sectional microstructural images and XRD patterns indicate that the α′ phase dominates parts fabricated by LPS whereas those fabricated using SPS consist of the α phase and the prior β phase due to the effect of remelting. Electron backscatter diffraction (EBSD) was used to analyze the grain distribution, preferred grain orientation, and grain size, which revealed that the parts fabricated using SPS had larger grains in both the XY and YZ planes than those fabricated using LPS, which is attributable to different cooling rates during the solidification process.