REDUCTILIZATION OF AN EMBRITTLED AMORPHOUS LA55AL25NI20 ALLOY BY WATER QUENCHING FROM SUPERCOOLED LIQUID

A water quenching treatment from supercooled liquid region was found to induce the ductilization of an amorphous La55Al25Ni20 alloy which was embrittled by annealing in a wide temperature range up to the glass transition temperature (T(g)). The tensile fracture surface appearance also changed from a shell-like pattern typical for the brittle amorphous alloy to pattern consisting of smooth and vein regions typical for the ductile amorphous alloy. There is no appreciable difference in the fracture surface appearance between the melt-spun and the ductilized alloys. The embrittled samples exhibit a reversible endothermic reaction resulting from the annihilation of the short-range ordering developed during annealing, accompanied by a significant decrease of an exothermic reaction. On the other hand, the water-quenched sample with good ductility does not have the endothermic reaction and exhibits only the exothermic reaction in the entire temperature range up to T(g). Accordingly, the reductilization caused by water quenching is presumed to destroy the structure stabilized by the annealing-induced structural relaxation so as to rather close to the quenching-induced disordered atomic configuration. This has been supported by the results of X-ray diffraction.