基于努氏硬度表征大块金属玻璃的力学性能

采用多种载荷对14种大块金属玻璃进行努氏硬度测试，结果表明努氏硬度随载荷的增加而降低，最后趋于稳定。利用Meyer定律、弹塑性变形模型、Hays-Kendall模型和变形阻力模型对材料的压痕尺寸效应进行分析，结果表明实验材料受到正压痕尺寸效应的影响，在压痕表面未产生裂纹时应采用较大载荷下趋于稳定的硬度值进行杨氏弹性模量E和屈服强度σy的分析。对于大多数实验材料，未修正的Marshall模型和Conway模型计算的杨氏弹性模量值偏大。Marshall模型中的参数α随着压痕对角线比值b′/d的增大而线性减小，Conway模型中的修正系数β随着压痕短对角线比值的平方(b′/b)2线性增加；对两模型进行修正时α和β可以分别用b′/d与(b′/b)2线性表示；同时发现金属玻璃的努氏硬度和杨氏弹性模量成正比，比例系数为0.0445。分别利用Tabor、Lockett、Yu、Marsh、Johnson和Vandeperre模型计算屈服强度时，除Johnson模型的计算值接近实际值外其它模型计算结果偏低，为了不同的模型能够得到正确的屈服强度，需要修正努氏硬度HK与名义硬度H之间的比例关系。当大块金属玻璃的努氏硬度小于6 GPa、玻璃态转变温度小于800 K时，缺口韧性KQ分别随着努氏硬度HK和玻璃态转变温度Tg线性增加。

Characterization of Mechanical Properties of Bulk Metallic Glasses Based on Knoop Hardness

A variety of loads were applied to test Knoop hardness of 14 kinds of bulk metallic glasses. The results showed that Knoop hardness decreased with the increase of load, and finally tended to be stable. Indentation size effect was analyzed using Meyer's law, the elastic-plastic deformation model, Hays-Kendall model and deformation resistance model, a positive indentation size effect was found. Under large loads when there was no crack on the indentation surface, hardness approached to a contant, which was used to calculate Young's elastic modulus E and Yield strength σy. For most experimental materials, Young's elastic modulus values obtained by Marshall model and Conway model are too large. The parameter α in Marshall model linearly decreased with the increase of the indentation diagonal ratio b′/d, and the correction factor β in Conway model linearly increased with the square of the indentation short diagonal ratio (b′/b)2. We proposed modified models with α and β being expressed linearly as b′/d and (b′/b)2 respectively. Meanwhile, it was found that the Knoop hardness of metallic glass was proportional to its Young's elastic modulus, and the proportionality coefficient was 0.0445. When the Yield strength was calculated using Tabor, Lockett, Yu, Marsh, Johnson and Vandeperre models respectively, the calculated results were low except for that of Johnson model giving results close to the actual values. The scaling relationship between Knoop hardness HK and nominal hardness H should be modified in order to obtain the correct yield strength by differrent models. The Notch toughness KQ of bulk metallic glass increased linearly with Knoop hardness HK and glass transition temperature Tg respectively when Knoop hardness is smaller than 6 GPa and glass transition temperature is smaller than 800 K.