NANOCRYSTAL DEVELOPMENT IN METALLIC GLASS

Abstract

The Metallic glass samples exhibit unique mechanical and physical properties at room temperature. A significant drawback is that it exhibits an inhomogeneous deformation behavior at temperatures below the glass transition due to the formation of localized shear bands which limits the potential application of advanced engineering materials. This drawback of metallic glass can be overcome by the isothermal annealing treatment on the super cooled liquid region at various temperatures to form the nanocrystalline dispersoids in the amorphous matrix. These dispersoids hinder slip by activating several slip planes simultaneously which appear as several shear bands on the sample surface. An increase in strength along with good ductility has recently been observed form Zr-Based metallic glasses with multiphase nanoscale microstructures. Isothermal annealing treatment of Zr55Cu30A110Ni5 metallic glass at various temperatures above the glass transition temperature was carried out to form the homogeneous dispersed phase inside the glassy matrix in the Differential Scanning Calorimetry (DSC). The glassy state crystallizes through an exothermic reaction due to the precipitation of the stable Zr2Cu crystalline phase inside the glass matrix forming a composite. The duplex phase (amorphous- nanocrystal) structure can improve mechanical properties of the metallic glass. Nanocrystalline precipitates increase the room temperature mechanical strength while maintaining micro plasticity for limited volume fractions of particles. Both the amorphous matrix as well as the Precipitates contributes to the overall strength of the material. A differential scanning calorimetry study was performed to understand kinetic changes that occur in this alloy at elevated temperature. The crystallization behavior of the metallic glass ribbon sample studied by XRD method. The metallic glass ribbon samples are isothermal annealed and subsequently subjected to mechanical test.