Easy glass formation in La₅₅Ni₂₀Al₂₅ by Bridgman solidification

Easy glass-forming alloy La₅₅Ni₂₀Al₂₅ was subjected to Bridgman unidirectional solidification at growth velocities between 0.34 mm/s and 4.5 mm/s through a temperature gradient of 15 K/mm. Results of X-ray diffraction confirm that the sample grown at 4.5 mm/s was fully amorphous whereas sample grown at 2.3 mm/s was partially amorphous with some crystalline structure and sample grown at 0.34 mm/s was basically crystalline. DSC results showed typical glass transition and crystallization for samples grown at 4.5 mm/s and 2.3 mm/s, in contrast to no transformation characterized by a flat line for sample grown at 0.34 mm/s. Values of T_g and T_x obtained from the fully amorphous sample grown at 4.5 mm/s are 493 K and 557 K respectively, resulting in a temperature span of 64 K between these two temperatures. These results confirm a critical cooling rate of 62.5 K/s for glass formation in La₅₅Al₂₅Ni₂₀ alloy and this rate is compared with critical cooling rates obtained by other methods for the same alloy as well as for other easy glass forming materials.