Microstructural and mechanical characteristics of zirconium alloy joints brazed by a Zr–Cu–Al-based glassy alloy.

Brazing characteristics of a Zr(Ti)–Cu(Fe)–Al glassy alloy was investigated using a Zircaloy-4 alloy as a base metal. A low melting temperature (solidus: 840 °C, liquidus: 880 °C) of the brazing alloy was obtained at the near-eutectic composition of Zr 55 Ti 5 Cu 25 Fe 5 Al 10 (at.%) designed by a partial replacement of Zr by Ti, and Cu by Fe from a well-known Zr 60 Cu 30 Al 10 ternary alloy. This quinary brazing alloy exhibited excellent melting and wetting characteristics and good compatibility with the base metal. At brazing temperatures below the liquidus of the brazing alloy, the joint consisted of a relatively fine dendritic structure ( α -Zr + Zr 2 Cu) with a massive segregation of Zr 2 Cu in the central zone by a eutectic solidification of the molten brazing alloy during a cooling stage, whereas a homogeneous joint was obtained at 890 °C with a predominant formation of acicular α -Zr phases holding an intercellular lamellar mixture ( α -Zr + Zr 2 Cu), which was produced by an isothermal solidification during a brazing holding time. The mechanical properties of the joints were strongly dependent on a degree of joint homogeneity, and the bonding strength of the joints was high enough to cause a fracture in the Zircaloy-4 base metal, when the central segregation of massive Zr 2 Cu was completely eliminated at the brazing temperature of 890 °C. [ABSTRACT FROM AUTHOR]