The influence of hydrogen content on the Zr-4 alloy diffusion bonding joint: From experiments to molecular dynamics simulations

Abstract

Bonding the Zr-4 alloy in the high temperature can lead to many problems, for example grain coarsening and large welding deformation resulting from high residual stresses. Hydrogenation is an effective approach to decrease the bonding temperature. In the present research, the influence of hydrogen contents on the microstructure evolution and shear strength of Zr-4 alloy joints were studied. The number of interface voids markedly decreased with increasing hydrogen content at 650 °C. A sound joint was obtained at the hydrogen content of 0.2 wt% hydrogen. This achieved joint had a shear strength of 244 MPa, and the fracture mode of the joint presented the brittle/ductile mixed mode. With the increase of hydrogen content, the flow stress of the hydrogenated Zr-4 alloy decreased due to the decomposition of zirconium hydrides. The plasticity of the joint enhanced with increasing hydrogen content in the view of electron backscatter diffraction (EBSD) results, and the kernel average misorientation increased from 0.11° to 0.77°. In addition, the diffusion behavior and diffusion coefficient of the Zr atoms were investigated by molecular dynamics simulation. The calculation results showed that hydrogen enhanced the diffusivity of the Zr atoms, and the diffusion coefficient of the Zr atoms accordingly increased by four orders of magnitude. The addition of hydrogen influenced the directly diffusion bonding process through two aspects: improvement of plasticity and enhancement of diffusion ability.