Coupling effect of bonding temperature and reduced interlayer thickness on the interface characteristics and quality of the diffusion-bonded joints of Zr alloys

Abstract

Zr705 alloys with 10-μm-thick Cu interlayers, bonded via vacuum diffusion bonding at 880–940 °C for 60 min, exhibited superior performance compared to previous studies on Zr705 alloys with 30-μm-thick Cu foil interlayers at the same temperature. The ultimate tensile strength (UTS) and elongation (EL) of the bonded joints increased with bonding temperature. The optimal UTS and EL (580 MPa and 32%, respectively) were obtained at 940 °C and are better than the optimal tensile properties obtained previously (30-μm-thick at 940 °C). The fracture form of the bonded joints was changed from brittle fracture at 880 or 900 °C to ductile fracture at 920 or 940 °C. A Zr–Cu intermetallic compound layer was formed on the bonding interface at 880 and 900 °C, which included Zr2Cu, ZrCu, Zr3Cu8, and ZrCu5 phases; the residual β phase was rich in Nb, and numerous Zr2Cu particles were precipitated along with this phase on the base material near the interface according to transmission electron microscopy analysis. At 940 °C, a broad Zr–Cu solid solution zone formed at the interface, in which no intermetallic compound was observed. The coarse grains with grain boundary migration were observed at the interface, and the entire base material exhibited a Widmanstätten microstructure at this temperature. The tensile tests and microstructure observations show that reducing the interlayer thickness lower the bonding temperature in some extent and improves the mechanical properties of bonded joints.