Elasticity and hardness of nano-polycrystalline boron nitrides: The apparent Hall-Petch effect
- Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan)
- Advanced Materials R and D Laboratories, Sumitomo Electric Industries, Ltd., Itami, Hyogo 664-0016 (Japan)
Nano-polycrystalline boron nitride (BN) is expected to replace diamond as a superhard and superstiff material. Although its hardening was reported, its elasticity remains unclear and the as-measured hardness could be significantly different from the true value due to the elastic recovery. In this study, we measured the longitudinal-wave elastic constant of nano-polycrystalline BNs using picosecond ultrasound spectroscopy and confirmed the elastic softening for small-grain BNs. We also measured Vickers and Knoop hardness for the same specimens and clarified the relationship between hardness and stiffness. The Vickers hardness significantly increased as the grain size decreased, while the Knoop hardness remained nearly unchanged. We attribute the apparent increase in Vickers hardness to the elastic recovery and propose a model to support this insight.
- OSTI ID:
- 22310947
- Journal Information:
- Applied Physics Letters, Vol. 105, Issue 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
- Country of Publication:
- United States
- Language:
- English
Similar Records
Yield strength and brittle-to-ductile transition of boron-nitride and gallium-nitride
Hexagonal-structured ε-NbN: ultra-incompressibility, high shear rigidity and a possible hard superconducting material