Improved ballistic performance of additively manufactured Ti6Al4V with α-β lamellar microstructures

Titanium alloys are attractive lightweight alternatives to steels for armour applications. However, their ballistic performance remains much less understood than their conventional mechanical performance. This research correlates the microstructural features of the Ti6Al4V alloy manufactured by laser powder bed fusion (LPBF) in as-built and post-heat treated conditions to its mechanical behaviour at high strain rates (up to 103 s−1) as well as ballistic performance. The results obtained indicate that post-LPBF heat treatment or in-situ LPBF microstructural control is capable of producing Ti6Al4V plates with ballistic protection capabilities comparable to or exceeding the requirement of the wrought Ti6Al4V armour military specification as per MIL-DTL-46077G. This was achieved despite these Ti6Al4V alloy plate samples having a lamellar α-β microstructure structure, which is considered highly undesirable under high strain rate deformation. It is shown that the increased thickness of α-lamellae by post-LPBF heat treatment and their reorientation are potentially the key reasons that are responsible for their exceptional ductility and improved ballistic performance. Other microstructural factors with a positive effect on the ballistic performance include prior-β grain size as a function of the powder layer thickness as well as the stage of the in-situ martensitic decomposition, which defines the hardness of the microstructure.