Glass formation in La-based La55Al25(NiCu)20 alloys by Bridgman solidification

Abstract

Five La-based La55Al25NixCu20-x (x = 0, 5, 10, 15, 20) alloys were subjected to Bridgman unidirectional solidification at growth velocities between 0.1 and 4.82 mm/s through a temperature gradient of 15 K/mm. The formation of the amorphous state of the resulting samples was confirmed by X-ray diffraction and differential scanning calorimetry. The critical cooling rates for glass formation in La55Al25Ni20, La55Al25Ni15Cu5, La55Al25Ni10Cu10, La55Al25Ni5Cu15 and La55Al25Cu20 were directly determined to be 67.5±6.8 K/s, 34.5±3.5 K/s, 22.5±2.2 K/s, 35.9±4.0 K/s and more than 72.3±8.0 K/s, respectively. With increasing Cu content the critical growth velocity shows a minimum phenomenon around 10 at.% Cu, indicating that the glass forming ability is the largest for the 10 at.% Cu containing alloy. The glass transition temperature (Tg) and the crystallization temperature (Tx) are independent of growth velocity for fully amorphous samples. The heat of crystallization (ΔHx) increased with increasing growth velocity.