Enhanced crack buffering of additively manufactured Ti–6Al–4V alloy using calcium fluoride particles

Abstract

Ti-based alloys fabricated by wire and arc additive manufacturing (WAAM) exhibit continuous grain boundaries of α phase (GB-α), which easily initiate cracks and provide a continuous crack propagation path. Herein, an activating flux of CaF2 particles was introduced into WAAM-fabricated Ti–6Al–4V alloy to tailor the microstructure for crack buffering (i.e., inhibit smooth propagation of cracks). The results showed that the addition of CaF2 particles disrupted the continuous GB-α through the dowel-like lamellar α phase (DL-α), which was primary α lamella deeply embedded in the adjacent prior-β grains. This microstructure imparted an optimal combination of strain and strength even in the presence of pores in the WAAM-fabricated Ti–6Al–4V alloy. The enhanced mechanical properties can be attributed to uniform plastic deformations and tendency to transgranular fracture of tensile specimens. DL-α relieved stress concentration at the grain boundary and guided cracks into the prior-β grain interior (i.e., avoided inter-crystalline fracture), thereby promoting the crack buffering effect. The study can provide theory guidance and data support for improving the mechanical performance of WAAM-fabricated Ti–6Al–4V alloy.