Thermodynamics of the stability of amorphous alloys of two transition metals

A scheme, recently proposed by Miedema and Niessen (MN), by which the concentration range is predicted in which amorphous binary transition metal alloys have high crystallization temperatures, has been tested for several alloy systems. The predictions are based on calculated values of the enthalpies of the amorphous phase and the f.c.c., h.c.p. and b.c.c. solid solutions. Thin films of W-Os, W-Ir, Ta-Re, Ta-Os, Ta-Ir, V-Pd, Nb-Pd and Ta-Pd were deposited at room temperature. The crystallization behaviour of films that were amorphous as deposited was investigated. For the 5d-5d systems, crystallization temperatures from 750 °C to 950 °C were observed. Using transmission electron microscopy and X-ray diffraction, some complex metastable phases were found as crystallization products. In agreement with the MN scheme plots of the crystallization temperature vs. average valence z̄ generally exhibit a maximum around -z = 6.7. However, the range of alloy compositions over which amorphous alloys are formed disagrees, in most cases, with the predicted one. We propose improvements for the calculation of the enthalpy curves.