Increased ductility of Ti-6Al-4V by interlayer milling during directed energy deposition

Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4 V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular alpha laths at the machined interfaces. The coarse alpha laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys.