Glass-Forming Ability, Thermal Stability, and Hardness of Rapidly Solidified Al-Ni-Y-Sc Alloy Ribbons and Rods

Abstract

The crystallization behaviors and thermal stability of (Al87Y8Ni5)100−xScx (x\u2009=\u20090, 1.0, 1.5) amorphous ribbons and alloy rods, produced by roller melt-spinning method and inductance casting, were investigated mainly by x-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The glass transition temperatures of the (Al87Y8Ni5)99.0Sc1.0 and (Al87Y8Ni5)98.5Sc1.5 alloy ribbons were found to be 201 and 197\xa0°C, respectively. Furthermore, the melting temperatures of the alloy ribbons decreased with the Sc content. This revealed that the glass-forming ability (GFA) of the metallic glass increased with increasing Sc content. Crystallization of (Al87Y8Ni5)100−xScx (x\u2009=\u20090, 1.0, 1.5) amorphous ribbons occurred in the temperature range of 200 to 400\xa0°C in three exothermic reaction stages. The peak temperatures of these three crystallization reactions shifted to higher temperatures at higher heating rates. The kinetic parameters for the first crystallization reaction, determined by Kissinger method, revealed that adding 1.5\xa0at.% Sc increased the activation energy for crystallization from 158 to 167\xa0kJ/mol. On the other hand, the cross-section morphology of the three different alloys revealed that a fully amorphous outer region and a partially crystallized core region formed in each alloy rod. It was also found that the thickness of the amorphous region increased with the Sc content, revealing a positive effect of Sc on the GFA.