Deformation-induced microcracking in Pd 40Ni 40P 20 metallic glass

Abstract

The free volume theory of plastic flow in metallic glasses leads to the prediction that during low temperature plastic flow metallic glasses should undergo substantial shear-induced dilatations, and that this effect is responsible for the localisation of the deformation into narrow shear bands. Several attempts have been made to measure the density change resulting from plastic deformation in metallic glasses, either by direct density measurements or by measuring changes in linear dimensions. In the course of a recent investigation of the slip line patterns produced during indentation of Pd/sub 40/Ni/sub 40/P/sub 20/ metallic glass it was found that extensive arrays of incipient cracks are formed around an indentation. These cracks are not visible, even in the scanning electron microscope (SEM), until the specimen is chemically etched: before etching the indentation process appears to be completely ductile. It seemed probable that similar crack arrays would be formed during other kinds of deformation in apparently fully ductile metallic glasses, and that these might be partly responsible for the very large density changes measured after deformation.