Quantification of the free volume in Zr 45.0Cu 39.3Al 7.0Ag 8.7 bulk metallic glasses subjected to plastic deformation by calorimetric and dilatometric measurements

Abstract

Zr 45.0Cu 39.3Al 7.0Ag 8.7 bulk metallic glasses (BMGs) were prepared using suction casting technique. Plastic deformations were carried out by cold rolling and high-pressure torsion (HPT). The absolute contents of free volume in the as-cast, preheated and deformed samples were determined by differential scanning calorimetry (DSC) and dilatometry using the free volume model (FVM). The parameters required in the FVM are experimentally determined to be b = 0.107, β = 642.1 kJ/mol, D * = 10.3 and T 0 = 496.9 K, respectively. The equilibrium free volume determined by these parameters is in good agreement with that calculated from previous enthalpy relaxation experiments, showing the reliability of the values of the parameters. It is found that the content of free volume in the as-cast sample is 0.533% with respect to the atomic volume of the BMG. The free volume in the HPT deformed sample is determined to be 0.672%, which is the largest among all the samples. The excess free volume introduced by cold rolling is found to increase with the deformation strain and show weak strain rate dependent behavior. Finally, attempts are made to simulate the experimental DSC curve using a bimolecular kinetics in the flow defect model. However, the result shows that the kinetics of free volume may be more complicated than as described as a bimolecular process.