Effect of Microstructure on Hydride Transition of TC4 Titanium Alloy

The diffusion behavior of hydrogen in lamellar and bi-modal TC4 alloys was investigated through electrochemical hydrogenation combined with multi-scale characterization techniques. The results show that after electrochemical hydrogen charging, the diffusion surfaces of lamellar and bi-modal samples present a gradient distribution of hydrogen concentration, and the thickness of the hydrogen diffusion layer of two samples is similar. The volume fraction of hydride in the diffusion surface of the lamellar sample is larger, hydrides preferentially form at the α/β interface and grow in the form of twin pairs into the α phase. In the case of the bi-modal sample, due to the relatively large equiaxed α grain size, hydrides cannot fill the entire α grain. Different hydride variants alternate in nucleation and growth near the α/β interface. TEM analysis results indicate that the hydrogenation nucleation in both microstructure samples presents a multi-level structural transformation mechanism regulated by stacking faults.