ENTHALPIES OF FORMATION AND CRYSTALLIZATION OF AMORPHOUS ZR1-XALX ANDZR1-XNIX ALLOYS - CALCULATIONS COMPARED WITH MEASUREMENTS

The enthalpies of formation of amorphous Zr1-xAlx and Zr1-xNix alloys have been calculated based on CALPHAD data and compared with experimen tally determined values. A direct extrapolation of the thermodynamic f unctions of the undercooled liquid significantly underestimates the st ability of the amorphous phase. When including the effects of the exce ss specific heat of the undercooled liquid, DELTAC(p), good quantitati ve agreement between the calculations and experimental data has been a chieved, in particular for the Zr-Ni case. Using the same DELTAC(p) fu nctions, the enthalpy of crystallization of the amorphous alloys in bo th systems has been computed and found to agree well with the same qua ntity directly obtained from calorimetric measurements. These calculat ed enthalpy of crystallization data have also been employed in an alte rnative approach to calculating the enthalpy of formation of the amorp hous alloys; such calculations are in excellent agreement with experim ental values in both Zr-Al and Zr-Ni cases. It is shown that the entha lpy-composition diagram measured or calculated using our approaches ca n be used as a good approximation to the free energy-composition diagr am in predicting the homogeneity range of the amorphous phase for low synthesis temperatures.