Evaluation of influence of microstructural features of LPBF Ti-6Al-4 V on mechanical properties for an optimal strength and ductility

Recently, Additive Manufacturing (AM) has established its potential in the biomedical industry due to its capability to produce customized biomedical implants with complex geometries. This study involves the fabrication of Ti-6Al-4 V parts using Laser based Powder Bed Fusion (LPBF) additive manufacturing process. Due to rapid solidification, the as-built Ti-6Al-4 V parts exhibit an increased strength and reduced tensile elongation because of the formation of non-equilibrium acicular martensitic α’ structure. Thus, the present investigation aims at analysing the influence of post-heat-treatment on evolution of microstructure, mechanical properties and fracture- behaviour of LPBF Ti-6Al-4 V alloys in the α + β range. The phase transformation occurs through martensitic α’ decomposition into stable α- and β-phases upon heat-treatment and impacts the mechanical properties significantly. The heat-treated samples showed a gradual drop in strength (∼24% max drop in UTS vs as-built) and hardness (∼35% max drop vs as-built) with increase in β-fraction, whereas the ductility showed a complex behaviour because of the detrimental effect of GB-α precipitation and coarsening. Furthermore, the effect of microstructure on fracture modes was studied. It was observed that the thickness, nature and distribution of GB-α affects the mechanical properties and fracture behaviour. Moreover, this work provides insights towards understanding the structure-property correlation bringing forth a better tailored microstructure to obtain a beneficial combination of ductility and strength for orthopaedic implants. •The as-built condition exhibits a hierarchical pattern consisting acicular martensite.•The heat-treatment effectively transformed the acicular martensite into stable α- and β- phases.•The precipitation and coarsening of GB-α along the prior β-grain boundary is affected by heat-treatment temperature and is very detrimental to ductility.•The nature and distribution of GB-α influences the fracture mode.