Post-processing-induced improvements in the bending behavior of SLM-produced Ti6Al4V alloy

This study presents a multiscale evaluation of the effects of various post-processing strategies, including machining, shot peening (SP), and heat treatment, on the static bending behavior of Ti6Al4V alloy produced by selective laser melting (SLM). Five specimen groups were prepared: as-built, milled, milled followed by traditional SP, milled followed by dual SP, and annealed before milling. To establish a detailed structure–property relationship, the study integrates surface roughness measurements, microstructural and fracture surface characterizations with three-point bending tests. Milling significantly improved surface quality, reducing the average surface roughness (Ra) from 17.05 μm in the as-built specimens to 0.43 μm in the only machined ones. This significant reduction contributed to higher bending strength and bending strain compared with the as-built specimens. While conventional SP slightly increased the surface roughness amplitude (Ra, Rz, and Rc), the secondary SP with smaller-diameter shots reduced roughness amplitude again and resulted in a more homogeneous surface topography. Machining alone improved bending strength by 23%, whereas dual SP yielded the highest strength with a 34% increase relative to the as-built specimens, due to induced compressive residual stresses, martensitic α′ lath refinement, reduced surface roughness, and higher dislocation density. Heat treatment transformed the martensitic α′ phase in prior β grains into an α + β structure, and the annealed and machined specimens exhibited a 264% increase in bending strain relative to the as-built specimens and 184% compared to the only machined specimens, with ductility enhancement primarily governed by the α + β transformation and supported by reduced surface roughness.