EASY GLASS-FORMATION IN LA55NI20AL25 BY BRIDGMAN SOLIDIFICATION

Easy glass-forming alloy La55Ni20Al25 was subjected to Bridgman unidir ectional 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 diff raction 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 cry stalline structure and sample grown at 0.34 mm/s was basically crystal line. 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 transfor mation characterized by a flat line for sample grown at 0.34 mm/s. Val ues 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 s pan of 64 K between these two temperatures. These results confirm a cr itical cooling rate of 62.5 K/s for glass formation in La55Al25Ni20 al loy and this rate is compared with critical cooling rates obtained by other methods for the same alloy as well as for other easy glass formi ng materials. (C) 1998 Elsevier Science B.V.