Study On Glass Forming Ability And Plastic Behavior Of Metallic Glass

Metallic glasses(MGs)usually exhibit superior mechanical-physical-chemical properties at the macroscopic scale,which has attracted the attention of scholars at home and abroad,but their severe preparation technology and fragility at room temperature of MGs restrict their wide application.Because of their unique atomic structure,the forming principle and deformation mechanism of MGs is different from traditional polycrystalline alloys.Therefore,it is of great significance to investigate the relationship between glass-forming ability(GFA)and thermodynamic characteristics of MGs and the evolution of shear band in plastic deformation of MGs,which is an important step for us to perceive them.This paper mainly studies the following two parts:1)GFA criteria;2)Numerical simulation of shear band evolution of different MG models.The main conclusions are as follows:1)Based on the classical nucleation theory,a new GFA criterion related to the characteristic temperature has been proposed asv(28)(T_x-T_g)?T_g?T_x/(T_l-T_x)³(where _gT,_xT and _lT are the glass transition temperature,the onset crystallization temperature and the liquidus temperature,respectively).The linear relationship between criterion and critical casting diameter(D_max)has been obtained by the correlation analysis with the critical diameter reported in the literature.The comparison and analysis of ten criteria shows that the interrelationship between?and critical diamete is better than others,and the calculated values of Fe-based MGs byvparameter exhibit smaller errors,which shows a better applicability and reliability for assessing the GFA,and it can reduce the workload of critical diamete determination to a certain extent.2)Based on the linear elastic Hooke's law,Mohr-Coulomb yield criterion and free volume model,the elastic-plastic constitutive model of MG is realized by secondary development in UMAT.According to the simulation results of the stress-strain relationship under uniaxial compression of different points in Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5MG which inside and outside the shear band,the relationship between the strain softening phenomenon and the free volume has been analyzed,and the result is obtained in good agreement with the experimental phenomena,which verify the correctness of the routine.In this paper,the mechanical behaviors of the ideal homogeneous model,the non-homogeneous model and the model with voids under the plane strain have been analyzed respectively.The increase in the compressed strain rate applied by the ideal homogeneous model causes an increase in the peak stress,the free volume change and which causes a more pronounced localization of the shear band.The shear band propagation always deviated from the direction of maximum shear stress with respect to the angle<45of the plumb plane.The initial free volume disturbance formed by the free volume bias distribution caused by the inhomogeneous structure will interfere with the initial sprouting site of the shear band,and the number of initial disturbance points will intensify the shear band evolution,causing an increase in the bearing strain.The shape and number of local structure voids formed during quenching will affect the shear band evolution,which interferes less with the propagation direction and causes an increase in peak stress and free volume change mainly.Local voids in the material will form local stress concentrations,which can cause more prone to instability.