Microstructural Evolution and Tensile Properties of Ti-Al-V Alloys Manufactured by Plasma Spraying and Subsequent Vacuum Hot Pressing

Ti-Al-V preforms were manufactured by low pressure plasma spraying (LPPS) from two different sizes of Ti-6Al-4V feedstock powders, and subsequently consolidated by vacuum hot pressing (VHP). During LPPS, a loss of alloying elements and an incorporation of [H] and [O] occurred, which were much significant for a smaller feedstock powder. Subsequent VHP completely removed [H] content, whereas a considerable amount of [O] remained. The microstructure of LPPS deposits comprised a splat-quenched lamellar structure, incorporating unmelted particles. The each splat contained (alpha)ʹ martensite plates and Ti hydrides which provided heterogeneous nucleation sites for recrystallization during subsequent VHP, transforming into an equiaxed (alpha) grain structure. The tensile properties of LPPS/VHP Ti-Al-V alloy were primarily affected by [O] content. An increase in [O] content up to 0.35 mass% increased tensile strength, but dramatically decreased ductility. Further [O] incorporation formed a large fraction of embrittled (alpha)-phase, resulting in a significant decrease in both tensile strength and ductility.