Thermal stability and glass forming ability of amorphous Hf2Co11B alloy

Abstract

Crystallization kinetics and crystalline structure of melt-spun fully amorphous Hf2Co11B alloys in as-quenched state and after annealing were investigated. Differential scanning calorimetry measurements in isochronal mode were performed with different heating rates q to characterize crystallization process. Three exothermal peaks occur during heating, with maxima at 868K, 888K and 926K (heating rate q=20K/min). Kissinger, Ozawa and Augis-Bennett models were used for the activation energy calculations. All three methods give similar values of Ea within experiment inaccuracy and its average value is equal to 343±15kJ/mol for the first, 468±40kJ/mol for the second and 435±5kJ/mol for the third crystallization peak. Additionally, frequency factor k0 values were determined using Augis-Bennett model to be of order of 1017–1024s−1. At the beginning of the first crystallization event nucleation and grain growth is three-dimensional and changes to one-dimensional at the end of the process. The semi-empirical Miedema's model was applied to calculate glass forming ability of the Hf2Co11B alloy. Formation enthalpy of amorphous phase is equal to −20.6kJ/mol, what fits in with rather moderate possibility of formation of amorphous phase using rapid quenching technique.