Microstructure of superplastic Zr65Al10Ni10Cu15 metallic glass

Zr65Al10Ni10Cu15 metallic glass ribbons prepared by melt-spinning was tensiled at 673 K (in supercooled liquid region) at various strain rates between 5 x 10(-4) s(-1) and 1.7 x 10(-1) s(-1). The microstructure of the ribbons after deformation was observed using HRTEM. As a result, it was found that high-strain-rate superplasticity was obtained at the strain rates of 1.7 x 10(-2) s(-1) and 5 x 10(-2) s(-1) with preserving amorphous structure. At the strain rates below 5 x 10(-3) s(-1), total elongation of the ribbons decreased with the progress of crystallization. By cross-sectional TEM observations, it was found that the crystallization of Zr65Al10Ni10Cu15 metallic glass started in the surface region of the ribbon and proceeded to the internal region. SEM observations showed that many microcracks perpendicular to the tensile direction were generated in the surface of the crystallized ribbons deformed in tensile, but no cracks were observed apparently in the surface of the ribbons deformed with preserving amorphous structure. Consequently, it can be said that high-strain-rate superplasticity of Zr65Al10Ni10Cu15 metallic glass is caused by good deformability of the supercooled liquid state, and that an amorphous structure and a flat surface without microcracks are preserved during the high-strain-rate deformation to failure.