Structural relaxation and plastic flow in amorphous La 50Al 25Ni 25

Abstract

The tensile deformation of amorphous La 50Al 25Ni 25 is studied in an extensive set of tensile tests at temperatures just below the glass transition temperature. Depending on the pre-annealing treatment, in many cases strain softening occurs during the tensile tests. Only in the case of a very short pre-annealing treatment does apparent strain hardening occur. After deformation, up to ε=0.3, all samples are tested by differential scanning calorimetry, which reveals that the glass transition peak depends on the temperature and strain rate during the tensile test, but not on the pre-annealing treatment. The entire set of experimental evidence can adequately be explained by the free volume concept. The conclusion is that during plastic deformation additional free volume is created as compared with thermal equilibrium, and the structure reaches a temperature and strain rate dependent steady state of disorder, i.e. amount of free volume. A quantitative description of this process, which should be envisaged as the production of a small amount of free volume during each flow event, is presented.