Abstract
Nanoscale dynamic transformations during tensile and compressive deformation of Zr65Al7.5Ni10Cu17.5 and Zr65Al7.5Ni10Pd17.5 bulk metallic glasses have been investigated. Although no apparent differences are observed in the stress-strain curves in the tensile deformation between the two alloys, fine striations and depression zones with viscous flow appear at the fracture surface near the edge in the Zr65Al7.5Ni10Pd17.5 alloy. Unlike the Zr65Al7.5Ni10Cu17.5 alloy and other bulk metallic glasses, the Zr65Al7.5Ni10Pd17.5 bulk metallic glass exhibits a large plastic strain of approximately 7% during compressive deformation. By detailed examination of the microstructure, we provide direct evidence for nanoscale multistep shear band formation in the Zr65Al7.5Ni10Pd17.5 metallic glass. A novel nanoscale structure where fcc Zr2Ni nanocrystalline particles are arranged in “bandlike” areas in the glassy matrix is observed near the compressive fracture tip. The suppression of the propagation of the shear bands due to dynamic nanocrystallization causes this structure. Furthermore, the results are recognized as a novel phenomenon, a nanoscale dynamic structural change by shear band propagation, and provide a new method for improving the mechanical properties of bulk metallic glasses.
