块体非晶合金的剪切带演变与结构研究

The development of shear bands and the structure change in bulk metallic glasses under quasi-static uniaxial compression

研究单轴准静态压缩时Zr基块体非晶合金的剪切带特征,结合热膨胀测试研究剪切引起的非晶合金结构变化.结果表明,初始剪切带彼此独立(εp<2%),形核和初始扩展方向具有随机性,然后分叉(εp>2%)和相互交割(εp≥6.49%),次生剪切带逐渐与受力方向成45°,剪切带的次生和扩展受切应力影响较大;变形初期(εp<3%),剪切变形伴随新生自由体积,对应的驰豫过剩自由体积增多,过冷液相区最大黏度增大;塑性应变进一步增大,剪切带相互交割,对应的驰豫过剩自由体积和黏度急剧减少.

The development of shear bands in Zr-based bulk metallic glasses with different plastic strain after undergoing quasi-static uniaxial compression was investigated.The structural changes in the samples were evaluated through the thermodilatometric analysis.The shear bands are separated and randomly distributed at the initial plastic deformation stage（εp2%）.Then they begin to branch and intersect with each other（εp≥6.49%）.The formation and propagation of the secondary shear bands gradually incline to 45° to the loading direction.This indicates that the branching and intersection of the shear bands are much affected by the shear stress.The initial formation of shear bands induces the production of free volume,corresponding to the increase in the relaxed excess free volume（REFV）and the maximum viscosity in the supercooled liquid regime.When the plastic deformation continues,the shear bands intersect with each other,corresponding to the rapid decrease in REFV and the viscosity.The mechanics for the variation of REFV and the viscosity with the plastic strains is discussed.