Ductility of a Ti-6Al-4V alloy produced by selective laser melting of prealloyed powders

Purpose The aim of the paper is the study of the change in the mechanical properties (and in particular in ductility), with the microstructure, of a biomedical Ti-6Al-4V alloy produced by different variants of selective laser melting (SLM). Design/methodology/approach Ti-6Al-4V alloy produced by different variants of SLM has been mechanically characterized through tensile testing. Its microstructure has been investigated by optical observation after etching and by X-ray diffraction analysis. Findings SLM applied to Ti-6Al-4V alloy produces a material with a martensitic microstructure. Some microcracks, due the effect of incomplete homologous wetting and residual stresses produced by the large solidification undercooling of the melt pool, are observable in the matrix. Owing to the microstructure, the tensile strength of the additive manufactured parts is higher than the strength of hot worked parts, whereas the ductility is lower. A pre-heating of the powder bed is effective in assisting remelting and reducing residual stresses, but ductility does not increase significantly, since the microstructure remains martensitic. A post-building heat treatment causes the transformation of the metastable martensite in a biphasic a-b matrix, with a morphology that depends on the heat treatment. This results in an increase in ductility and a reduction in strength values. Originality/value The study evidenced how it is possible to obtain a fully dense material and make the martensite transform in Ti-6Al-4V alloy through the variation of the SLM process. The stabilization of the microstructure also results in an improvement of the ductility.