Deformation in a Zr57Ti5Cu20Ni8Al10 bulk metallic glass during nanoindentation

Nanoindentation experiments of a Zr57Ti5Cu20Ni8Al10 bulk metallic glass were performed with indentation loads ranging from 200 to 2000 μN. Both the indentation hardness and the reduced contact modulus decreased with the increase in the indentation load due to the propagation of shear bands underneath the indenter – the occurrence of a softening effect. The ratio of the indentation hardness to the reduced contact stiffness was a function of the reciprocal of the indentation depth. Based on the concept of diffusion-induced stresses, a one-dimensional constitutive relation between the change of the excessive free volume and the flow stress was proposed. The indentation-size effect as observed in the indentation tests was explained through the consideration of the contribution of the strain gradient in the constitutive relation.