Effects of chemical composition on the structural relaxation in ternary Zr-Cu-Al bulk glassy alloys studied by EXAFS and positron annihilation techniques.

Abstract

ABSTRACTMechanical properties and thermal stability of bulk glassy alloys depend on their chemical composition ratios, although their detailed local structures especially around free volume have not been clarified yet. In order to know the origin of property dependence on alloy composition in Zr-Cu-Al ternary bulk glassy alloys in a view point of atomic scale, positron annihilation lifetime, coincidence Doppler broadening (CDB) and EXAFS (extended X-ray absorption fine structure) measurements have been employed for eutectic Zr50Cu40Al10 and hypoeutectic Zr60Cu30Al10 bulk glassy alloys before and after structural relaxation by annealing below glass transition temperature Tg.The result of CDB experiment, which represents the electron momentum distribution around free volume, shows that significant atomic reordering around free volume does not take place by the annealing in each alloy. Besides, CDB ratio profiles for each alloy suggest that the fraction of Zr atom around free volume does not match the chemical composition of each alloy system. Change in positron lifetime, which is proportional to the size of free volume, during annealing for hypoeutectic alloy almost remains unchanged.