The Study Of Size Effects And Nanocrystal On The Deformation Behavior Of ZrCu Amorphous Alloy

Metallic glasses (MGs) are relatively new materials that have many excellentproperties, such as high strength, high elastic limit and high corrosion resistance. One ofthe major drawbacks for monolithic BMGs is limited ductility due to highly spontaneousstrain localization within a narrow shear band during the plastic deformation process. Inthis paper, we use molecular dynamics simulations study the effects of reduce model sizeand induce second phase-nanocrystals on the plasticity of MGs, and we further investigatethe mechanism of size effects and the nanocrystals on the plastic deformation of MGs.We find that with the model size gradually decrease its deformation behaviourevolves from highly localized shear band formation in D=20nm model to local strain tendto be more evenly distributed in D=9-7nm, and eventually in D=3.6nm model a fullyhomogeneous deformation. Through statistic we found that in the smallest size modelthere are more than62%atoms participate in the deformation, in the limited area theintense interaction between those atoms lead to them presents a state of disperseddistribution, making them share the strain caused by the deformation and avoid stressconcentration.The crystallization process of ZrCu amorphous alloy during isothermal annealing isstudied with molecular dynamics simulations, and find that the crystallization processexist three transition stages:(1) the nucleation of the crystals in the amorphous matrix;(2)the growth of the crystal nuclei;(3) the coarsening of the crystal grains. Then weinvestigated the structure evolution sites induced by stress and high temperature and findthat the crystalline phase induced by high temperature would occupy the preferred sites ofshear transformation zones (STZs), forcing STZs to form in other parts of the amorphousmatrix, which alters the path of shear bands in nanocrystal-metallic glass fundamentally.Meanwhile, more STZs are activated in rest parts of the amorphous matrix when thevolume fraction of nanocrystals is13.5%, significantly enhancing the plasticity ofnanocrystal metallic glass. During the process of interaction between shear bands andnanocrystals there exist two deformation mechanism bypass and cut, meanwhile, the crystal phase dissolution and its lattice type changes.