Indentation Induction Of Zr <sub> 65 </ Sub> Al <sub> 7.5 </ Sub> Cu <sub> 12.5 </ Sub> Ni <sub> 10 </ Sub> Ag <sub> 5 </ Sub> Alloy Crystallization Kinetics

In this paper, the microstructure evolution of Zr₆₅Al_7.5Cu_12.5Ni₁₀Ag₅ metallic glass during indentation at room temperature is investigated by high resolution transmission electron microscopy (HRTEM). And the finite element simulation is used to evaluate the effective stresses and strains on the different deformation regions during the Vickers indentation of the metallic glass. The influence of the stress on the nucleation activation energy and the nucleation rate and the activation energy for growth is investigated. The driving force for the microstructure changes due to plastic deformation is discussed. The main conclusions are obtained as following:The spherical crystals about 60 nm are observed under the indenter tip, and crystals larger than 1μm are found under the indenter edges. The crystallization behaviors of the Zr₆₅Al_7.5Cu_12.5Ni₁₀Ag₅ amorphous alloy due to indentation are closely with the compressive stress, which indicates that the compressive press is one critical factor influencing on the deformation-induced crystallization behaviors.The results of finite element simulation show that the compressive stress under the indenter tip is the largest than other regions. Under the intender edges the compressive stress become smaller and smaller away from the tip region. The equivalent plastic strain under the indenter tip reaches 73 percent and no fracture occurs. The equivalent strain reduces from 45% to 35% on the indenter edge regions away from the tip region. The plastic deformation during indentation is obvious an inhomogeneous mode.The activation energies for nucleation on the different plastic deformation regions are closely with the compressive stresses. The larger compressive stress under the indenter tip results in lower activation energy. And the activation energies for nucleation under the indenter edges are much larger due to the smaller compressive stresses. On the other side, the larger compressive stress results in larger activation energy for nuclei growth. In this sense, larger compressive stress is favorable for the formation of nanocrystals during plastic deformation.