Abstract
The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf. Results from the investigation indicate that the measured microhardness exhibits an indentation load dependence. Based on the results, we present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyer's law, Li and Bradt's proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteri's multifractal scaling law (MFSL). The best correlation between literature-cited load-independent Vickers microhardness values, the measured values, and applied models was achieved in the case of the MPSR and the MFSL models.
Highlights
With hardness values reported to range between 24 GPa and 45 GPa [1, 2], boron suboxide (B6O) is sometimes considered to be the third hardest material after only diamond and cubic boron nitride (∼60 GPa) [2]
The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf
We present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyer’s law, Li and Bradt’s proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteri’s multifractal scaling law (MFSL)
Summary
With hardness values reported to range between 24 GPa and 45 GPa [1, 2], boron suboxide (B6O) is sometimes considered to be the third hardest material after only diamond (from ∼70 to ∼100 GPa) and cubic boron nitride (∼60 GPa) [2]. Despite the intensive research efforts, the commercial applications are yet to be realized partly because of (a) the low fracture toughness of polycrystalline B6O [7] and considerable practical challenges in the densification of that material [2, 6, 7] by hotpressing, (b) stoichiometric B6O samples that are not easy to synthesize [1, 2], (c) poor crystallinity [1, 7], and (d) numerous mechanical properties of the material that are still poorly understood [8]—indentation size effect (ISE) in microhardness measurements is one such property. The aim of this paper is twofold: (1) to report experimental data on the microhardness of hot-pressed B6O determined by Vickers pyramidal indentation and (2) to critically examine the ISE phenomenon by means of a comprehensive intermodel
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