Ductility improvement due to martensite α′ decomposition in porous Ti–6Al–4V parts produced by selective laser melting for orthopedic implants.

Ti–6Al–4V parts obtained by selective laser melting typically have an acicular α′ martensitic microstructure whose ductility is low. Thus, post-heat treatments are useful for increasing ductility. In this work, the effects of sub-β- transus heat treatments on the mechanical properties of Ti–6Al–4V parts with porous structures are correlated with martensite α′ phase decomposition. The precipitation of β phase and the gradual transformation of α′ into α phase by the diffusion of excess vanadium from α′ to β phase are proposed to be the main events of martensite α′ phase decomposition in parts fabricated by selective laser melting. The heat treatment performed at 650 °C for 1 h produced no microstructural changes, but the samples treated for at the same temperature 2 h showed a fine precipitation of β phase along the α′ needle boundaries. The heat treatment performed at 800 °C for 1 or 2 h produced a fine α+β microstructure, in which β phase are present as particles fewer in number and larger in size, when compared with the ones present in the sample heat-treated at 650 °C for 2 h. Heat-treatment of the parts at 800 °C for 2 h proved to be the best condition, which improved the ductility of the samples while only slightly reducing their strength. [ABSTRACT FROM AUTHOR]