Investigating phase transformation, densification and diffusion mechanism of TiH2 powder to achieve a high ductile Ti6Al4V alloy

The challenges of micro-pores resistant to closure and significant ductility loss during the pressureless sintering of titanium (Ti) alloy powder mixtures have been overcome through an optimized design that capitalizes on the role of hydrogen (H). Explore novel mechanisms of hydrogen effects on phase transformation and densification during sintering, and innovatively fabricated unique microstructure and mechanical properties. The study employs thermodynamic calculations and analyses to understand the effect of dehydrogenation on the element diffusion mechanism. It optimizes sintering parameters to develop a bimodal microstructure featuring equiaxed α-Ti around the primary grain boundary α. More cracks in brittle powder compact enhanced micropore closure, leading to a high density with uniform element diffusion. The phase transition of H in the early stages creates lattice and surface defects, activating rapid diffusion channels at lower temperatures and reducing the apparent activation energy substantially compared to pure Ti. The optimized bimodal structure exhibits superior mechanical properties, maintaining a strength of 969 MPa while achieving a ductility of 16.8%. This research provides new insights into H applications in Ti powder metallurgy, achieving the expansion of titanium alloys into cost-effective domains.