Pre-hydrogenation metallurgy for Ti-3Al-5Mo-4.5V alloy with high density and mechanical properties

Abstract

The present work proposes a novel master-alloy pre-hydrogenation powder metallurgy (MAPH) method to fabricate the TC16 (Ti-3Al-5Mo-4.5V) alloy, which overcomes the challenge of low sintering density due to the high percentage of alloying powders (APs) and the presence of Mo element. The relative density of sintered TC16 alloys increases with the Ti-addition in APs, i.e., ∼99.2% and ∼99.4% for sintered TC16 alloys based on pre-hydrogenated 7.5Ti-3Al-5Mo-4.5V (7.5TiMA-Hx) and 12.5Ti-3Al-5Mo-4.5V (12.5TiMA-Hx) powders, respectively. The APs were successfully modified to be brittle and hydrogen-containing, which exhibits similar pressing and sintering characteristics as TiH2 powders. The increased relative density could be ascribed to the brittleness of 7.5/12.5TiMA-Hx, in which particles show sharp corners that can form interlocked structures with TiH2 particles during pressing. Furthermore, the 7.5/12.5TiMA-Hx and TiH2 powder particles release H2 and shrink simultaneously during sintering, which minimizes the difference in volume mismatch between particles and promotes elemental diffusion. The sintered TC16-7.5TiMA-Hx alloy achieves excellent mechanical properties, i.e., an ultimate tensile strength of ∼1004.6 MPa, a yield strength of ∼934.2 MPa and an elongation of ∼15.8%, due to the low porosity and acceptable impurity contents. However, the excessive O and N elements in the sintered TC16-12.5TiMA-Hx alloy can induce premature intergranular fracture, resulting in decreased ductility. Therefore, the innovative MAPH technique is promising in obtaining high density sintered Ti alloys with excellent mechanical properties.