p Introducing omega and O ' nanodomains in Ti-6Al-4V: The mechanism of accelerating alpha ->beta transformation kinetics via electropulsing

Conventional kinetics theory for diffusion-controlled phase transformation shows that the reverse tran-sition should lag behind the temperature rise through rapid heating, i.e., overheating is required. In this work, we found that the & beta;-transus temperature decreased by-50 & DEG;C during studying the & alpha; -& beta; transformation in Ti-6Al-4V alloy via electropulsing treatment (EPT). The calculation suggests that the acceleration of transformation kinetics cannot be fully explained by Joule heat and athermal effects of the electromigration effect and electron wind theory. The microstructural evolution during EPT was sys-tematically investigated utilizing scanning electron microscope (SEM), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), transmission Kikuchi diffraction (TKD), and transmission electron micro-scope (TEM). Microscopic analysis shows that the nano-sized & omega; and O ' phases formed in the & beta;phase, which causes large numbers of lattice distortion regions. The defects are conducive to accelerating the bulk diffusion of alloying elements in & beta;. Moreover, the nanodomains limited the growth of martensite, therefore nanocrystalline martensite formed after quenching. These findings develop the understanding of the destructive effect of current on metallic crystal, which will help to guide microstructural regulation in titanium and other alloys.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Conventional kinetics theory predicts that the reverse transition in diffusion-controlled phase transformation requires overheating. However, this study found that the β-transus temperature decreased by 50℃ during the α-β transformation in Ti-6Al-4V alloy through electropulsing treatment (EPT). Microscopic analysis revealed the formation of nano-sized ω and O' phases in the β phase, promoting alloying element diffusion and inhibiting the growth of martensite, resulting in the formation of nanocrystalline martensite after quenching.