试样尺寸对镁基块体金属玻璃压缩力学行为的影响

Effects of sample sizes on compressive mechanical behaviors of Mg-based bulk metallic glasses

研究试样直径和高径比对3种镁基块体金属玻璃Mg65Cu25Gd10、Mg65Cu20Ni5Gd10和Mg75Ni10Gd10压缩变形行为的影响,探讨镁基块体金属玻璃断裂模式的转变机制。压缩应力—应变曲线和断口扫描电镜观察结果表明:镁基块体金属玻璃Mg65Cu25Gd10、Mg65Cu20Ni5Gd10和Mg75Ni10Gd10在压缩条件下可在3个不同的变形阶段发生断裂,第1个是弹性变形阶段,在此变形阶段金属玻璃都以解理方式断裂,无塑性;第2个变形阶段的断裂为解理和剪切混合方式断裂,金属玻璃具有一定的剪切塑性变形;第3个变形阶段为稳定剪切锯齿塑性流变阶段,在此变形阶段金属玻璃都是以剪切方式断裂,具有稳定的塑性变形;镁基块体金属玻璃的断裂模式与尺寸有关,减小试样的直径和高径比都有利于块体金属玻璃由解理断裂向剪切断裂的转变,强度和塑性也相应地得到提高。

The effects of the as-cast diameter and aspect ratio on the compressive deformation behaviors of three Mg-based Mg65Cu25Gd10,Mg65Cu20Ni5Gd10 and Mg75Ni15Gd10 bulk metallic glasses（BMGs） were investigated.The mechanism for the transition of fracture modes of Mg-based BMGs was also discussed.The results from the stress-strain curves and fracture morphologies observed using scanning electron microscope（SEM） show that these Mg-based BMGs can fail at three different deformation stages under compression.The first stage is within the elastic regime,where the BMGs fail in a cleavage mode without plasticity.The second stage is in the range where the BMGs fail in the cleavage mode combining with the shear mode with a certain plastic deformation.The third stage means the serrated plastic deformation.In this stage,the BMGs fail in a pure shear mode after the obvious plastic serration.The fracture modes of these Mg-based BMGs are correlated with the sizes of the samples.Decreasing both the as-cast diameter and aspect ratio of the sample can favor the transition from the cleavage fracture to the shear fracture,resulting in higher strength and larger plasticity for the Mg-based BMGs.