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Solidification and crystallization behaviour of bulk glass forming alloys

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2007
Aybar, Sultan
The aim of the study was to investigate the crystallization kinetics and solidification behaviour of Fe60Co8Mo5Zr10W2B15 bulk glass forming alloy. The solidification behaviour in near-equilibrium and non-equilibrium cooling conditions was studied. The eutectic and peritectic reactions were found to exist in the solidification sequence of the alloy. The bulk metallic glass formation was achieved by using two methods: quenching from the liquid state and quenching from the semi-state. Scanning electron microscopy, x-ray diffraction and thermal analysis techniques were utilized in the characterization of the samples produced throughout the study. The choice of the starting material and the alloy preparation method was found to be effective in the amorphous phase formation. The critical cooling rate was calculated as 5.35 K/s by using the so-called Barandiaran and Colmenero method which was found to be comparable to the best glass former known to date. The isothermal crystallization kinetics of the alloy was studied at temperatures chosen in the supercooled liquid region and above the first crystallization temperature. The activation energies for glass transition and crystallization events were determined by using different analytical methods such as Kissinger and Ozawa methods. The magnetic properties of the alloy in the annealed, amorphous and as-cast states were characterized by using a vibrating sample magnetometer. The alloy was found to have soft magnetic properties in all states, however the annealed specimen was found to have less magnetic energy loss as compared to the others.