Heterogeneous microstructure evolution in Ti-6Al-4V alloy thin-wall components deposited by plasma arc additive manufacturing

Several Ti-6Al-4V layers were deposited using pulsed plasma arc additive manufacturing (PAM). Epitaxial growth of prior β columnar grain is inhibited by pulsed perturbation, which results in formation of columnar grain with near-equiaxed grains. The horizonal layer bands (LBs) is observed after depositing 6 layers, which is absent in prior three layers. LB region deposited by PAM can be attributed to the precipitation of secondary α nano dispersoids growing along {10-10} orientation, which finally turn into α colonies under sufficient thermal cycles in the both range of β-transus and recrystallisation temperatures. Dispersion strengthening of the α lamellae with α nano contributes to an increase in the microhardness. The phase transformation (β → α) follows Burges oriention relationship resulting in triangular stars or rhombic patterns analysised by Electron Backscattered Diffraction.413