In situ TEM investigation on the microstructure and phase evolution of hydrogenated Zr-4 alloy

Bonding of Zr-4 alloy at high temperature risked the safe run of nuclear reactors. The diffusion bonding of Zr-4 alloy could be realized at low temperature by hydrogenation. In situ heating transmission electron microscopy was used to observe the microstructure and phase evolution of hydrogenated Zr-4 alloy during heating from room temperature to 650 degrees C to clarify the bonding mechanism of Zr-4 alloy. Zirconium hydrides gradually decomposed during the heating process and beta-Zr phase formed in the matrix as a result. The observed decrease in the beta phase transus temperature caused by hydrogen addition was about 210 degrees C. Results indicated that diffusion bonding of Zr-4 alloy can be achieved at lower temperature via hydrogenation because the beta phase with bodycentered cubic structure has better deformation ability.