Thermal Stability and Crystallization Kinetics in Y-Based Metallic Glasses

Abstract

The glass-forming ability (GFA) and thermal stability of Y56–xScxAl24Co20 (0 ≤ x ≤ 18) alloys produced by melt spinning and suction casting have been investigated. The results show that the addition of a Sc element improves the GFA of Y-based metallic glasses, and the Y41Sc15Al24Co20 alloy has a reduced glass transition temperature Trg (=Tg/Tl) as large as 0.641. A new bulk metallic glass (BMG), Y41Sc15Al24Co20, with a diameter of 5 mm was successfully fabricated. The superior GFA after the Sc addition can be attributed to the ability of Sc to effectively alleviate the detrimental effect of oxygen as well as appropriate atomic-size mismatch and large negative heat of mixing among constituent elements. Crystallization kinetic studies show that the activation energies for the Y41Sc15Al24Co20 BMG are Eg = 4.92 eV and Ex = 3.18 eV, for the glass transition and crystallization, respectively, which are the highest in all known rare-earth (RE)–based BMGs. The values of the fragility parameter m for the Y56Al24Co20 and Y41Sc15Al24Co20 BMGs are 72 and 42, respectively. The significant decrease in m implies that the GFA and the thermal stability increase with the addition of Sc in the Y56Al24Co20 alloy.