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| Characterization of Mechanical Properties of Bulk Metallic Glasses Based on Knoop Hardness |
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Abstract 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.
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Received: 30 July 2020
Published: 27 August 2021
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2021, Vol. 42 
