Numerical Study Of Toughening Mechanisms Of Bulk Metallic Glass Composites

Bulk metallic glasses have many unique properties, eg, high strength, high hardness, good wear resistance, good corrosion resistance and excellent soft magnetic properties because of its special atomic structure configuration. However, during the deformation of BMGs, local shear deformation will occur and then make single or multiple shear bands formed due to the lack of hardening mechanism at room temperature, which makes the BMGs very brittle and fail catastrophically. Researchers focus on the BMG toughening mechanisms by introducing the crystalline second-phase and ensure the composites with high strength and good toughness. At present, most of the researches in mechanical properties of metallic glass composites are only stayed in experiment. In this paper, simulations to the evolution of shear band and crack growth are performed to demonstrate the effect of second-phase on the toughness in BMG. Main researches are listed as follows:(1) Free volume based constitutive model, which is incorporated into ABAQUS finite element code as a user material subroutine, is applied in the simulation of shear band deformation in bulk metallic glass (BMG) matrix composites under the monotonic tension. The effects of the volume fraction, shape, distribution and material parameters of particles on the shear banding evolution and ductility of the metallic glass matrix composites are discussed. Numerical results show that an increase in the volume fraction of particle reduces the overall stress of the BMG. The toughness of BMGs is better when the volume fraction of particle is between 8%to 12%. Particle spacing also plays an important role. Round particle can improve the toughness of the composites by comparing to others. An increased yielding stress of particle can enhance the stress response of the composites and enhance the resistance of particle to be sheared. However, if the yielding stress of particle is low, it is expected that the soft particles would be easily sheared by the shear band.(2) The interface in the composites can easily be destroyed, so it is necessary to consider the failure process of imperfect interface. During the simulation, the interface is represented by using the Cohesive element. Numerical results show that the destruction of the interface is divided into three steps:no debonding, debonding extension and complete debonding. An increased elastic module of interface can enhance the elastic module and yield stress of the composites. It shows that a good interface can ensure a sufficient stress transfer between the matrix and particles.(3) Prefabricated a crack, the effects of the crack on shear band deformation and concentration of free volume in bulk metallic glass matrix composites are investigated. Numerical results show that a higher concentration of free volume will be generated in the zone of crack tip generally and lead to branching of the shear band. Center crack can reduce the degree of softening of the composites comparing to edge one. An increased number of cracks can reduce the stress response and the degree of softening of the composites.