Structural relaxation and plastic flow in amorphous La50Al25Ni25

The tensile deformation of amorphous La50Al25Ni25 is studied in an extensi ve set of tensile tests at temperatures just below the glass transition tem perature. Depending on the pre-annealing treatment, in many cases strain so ftening occurs during the tensile tests. Only in the case of a very short p re-annealing treatment does apparent strain hardening occur. After deformat ion, up to epsilon = 0.3, all samples are tested by differential scanning c alorimetry, which reveals that the glass transition peak depends on the tem perature and strain rate during the tensile test, but not on the pre-anneal ing treatment. The entire set of experimental evidence can adequately be ex plained by the free volume concept. The conclusion is that during plastic d eformation additional free volume is created as compared with thermal equil ibrium, and the structure reaches a temperature and strain rate dependent s teady state of disorder, i.e. amount of free volume. A quantitative descrip tion of this process, which should be envisaged as the production of a smal l amount of free volume during each flow event, is presented. (C) 2000 Else vier Science S.A. All rights reserved.