Supercooled melting in multicomponent Zr–Al–Cu–Ni diffusion couples

Diffusion couples combining a hcp Zr90Al10 supersaturated solid solution with a fcc Cu64Ni36 solid solution were annealed at 410 °C for different times. The reaction at the interface was investigated by transmission electron microscopy and energy dispersive x-ray spectroscopy. The investigations show the formation of a noncrystalline layer at the interface between the two solid solutions that grows to a maximum thickness of more than 0.3 mm. Concentration profiles reveal that two noncrystalline phases coexist in the diffusion couple. One is Ni-rich and was in the amorphous state during the reaction at 410 °C. The other phase is Zr-rich and grew in its supercooled liquid state. This novel supercooled melting process has not been previously observed in a solid state reaction. Kinetic and thermodynamic aspects that contribute to the high thermal stability of the Zr–Al–Ni– Cu in the supercooled liquid are discussed. © 1996 American Institute of Physics. @S0003-6951~96!00821-2#