The microstructure evolution of Zr60Al15Ni25 bulk metallic glass during rolling at room temperature is investigated by differential scanning calorimetry(DSC),high-resolution transmission electron microscopy(HRTEM) and selected area electronic diffraction(SAED).The HRTEM images show that shear bands are produced in the rolled specimens,indicating the essence of inhomogeneous deformation due to rolling,and that there exist nanocrystals with size of about 5-10 nm in the transition regions between the shear bands and the undeformed matrix in the rolled specimens with deformation degrees of 80% and 95%.Based on the polyhedral structure model and the shear transformation zone(STZ) theory,the influence of viscous flow,free volume,viscosity and the stress situation on the crystallization behaviors in the metallic glass during rolling is discussed.
YAN ZhiJie,YAN Jun,HU Yong & DANG ShuE School of Materials Science and Engineering,Taiyuan University of Science and Technology,Taiyuan 030024,China
The microstructure of as-cast Zr60Al15Ni25 bulk metallic glass was investigated by high-resolution transmission electron microscopy. It is found that there exist numerous short-range order regions （SRORs） in the metallic glass though it is identified to be amorphous by X-ray diffraction method. Furthermore, the amorphous degree shows a close correlation with the microstructure of corresponding mother ingot. The crystallization kinetics was investigated by differential scanning calorimetry under isochronal and isothermal conditions. The results show that the crystallization is triggered by the growth of the pre-existing SRORs and the growth is three-dimension diffusion-controlled. The amorphous degree of Zr60Al15Ni25 bulk metallic glass considerably influences its crystallization kinetics, namely, the more homogeneous distribution of atoms results in a more sluggish nucleation behavior.
