Thermal Decomposition of Massive Phase to Fine Lamellar α/β in Ti–6Al–4V Additively Manufactured Alloy by Directed Energy Deposition

The occurrence of a massive phase (α_m) transformation and a thermal decomposition of an α_m to fine lamellar α/β with an α lamellar width of approximately 1 µm have been identified in additively manufactured Ti–6Al–4V alloy by directed energy deposition. The β to α_m phase transformation during additive manufacturing generated a high dislocation density, which was calculated by the kernel average misorientation. This caused a significant change in the Gibbs free energy of α, resulting in the nucleation of the β phase becoming preferable in the area with high dislocation density at temperature below the β-transus temperature. Subsequent annealing at 850 °C altered the massive morphology to lamellar due to the formation of a β phase between α lamellar boundaries. Graphical Abstract:

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