抄録
Viscous flow property of bulk metallic glasses (BMGes) at the supercooled liquid temperature range has already been applied to the practical net shape forming. At the higher temperature over 0.9Tg (Tg is the glass transition temperature of BMG), the Young’s modulus and yield stress of BMG drastically decrease, meanwhile the elongation reaches 40～50%. Thus, the hot working at this temperature range is much possible to be used for the plastic molding with the higher precision. The tensile tests of BMGes at such a high temperature report that the stress overshoots after the elastic limit and gradually decreases until the saturated plastic flowing, which is sensitive to the temperature and strain rate. The present study aims to investigate the plastic deformation behaviors of the initial yielding condition and the cyclic plastic hardening property related to the subsequent yielding condition at the high temperature using elastic-plastic Finite Element Method with the mean stress dependence and the defects density evolution law. The initial yielding can be well predicted by using Drucker-Prager yield criterion with the mean stress dependence parameter of κ=0.09 and the elastic limit as the yield stress of Zr-base BMG. The kinematic hardening by Prager-type back stress under cyclic uniaxial compressive and tensile loadings changes the stress overshoot behaviors. The defects density is accumulated at the reversed strain and is diminished at the zero strain. The plastic flow under the cyclic uniaxial compression is represented by the zero balance between the defects density nucleation and annihilation rates.
