Superplastic deformation behavior and microstructure evolution mechanism of hydrogenated Ti-4.5Al–3V–2Mo–2Fe alloy

This research investigates the superplastic deformation behavior and microstructure evolution of Ti-4.5Al–3V–2Mo–2Fe (SP700) alloys with varying hydrogen contents. Uniaxial tensile tests reveal that 0.1 wt% H SP700 alloy reduces the optimal superplastic forming (SPF) temperature by 20 °C, while only decreasing the elongation by 17 % compared to the original material. The incorporation of hydrogen promotes dynamic recrystallization (DRX), alleviates stress concentration, and significantly inhibits excessive grain growth, reducing the grain size at the fracture from 5.1 μm to 4.2 μm. However, a higher hydrogen content (0.2 wt%) leads to localized hydrogen enrichment, resulting in β-phase hardening and a substantial decline in elongation. Hydrogen notably lowers the β-transus temperature, with the increase of hydrogen content, the optimum superplastic temperature decreases synchronously with the phase transition temperature. During superplastic deformation, hydrogen rapidly diffuses through dislocation networks, accumulates in high strain regions, and facilitates the precipitation of primary α phase (α_p) in a rod-like morphology. Compared to uniaxial tension, the multiaxial stress state in superplastic bulging promotes uniform hydrogen diffusion, delays localized hydrogen enrichment, and maintains stable superplasticity. At the reduced optimal superplastic temperature (20 °C lower), the 0.1 wt% H alloy demonstrates comparable forming limits to the original material, while the 0.2 wt% H alloy exhibits significantly inferior plasticity.