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

Abstract

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 α′ martensite plates and Ti hydrides which provided heterogeneous nucleation sites for recrystallization during subsequent VHP, transforming into an equiaxed α 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 α-phase, resulting in a significant decrease in both tensile strength and ductility.