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Title: Elasticity and hardness of nano-polycrystalline boron nitrides: The apparent Hall-Petch effect

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.
Authors:
; ;  [1] ;  [2]
  1. Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan)
  2. Advanced Materials R and D Laboratories, Sumitomo Electric Industries, Ltd., Itami, Hyogo 664-0016 (Japan)
Publication Date:
OSTI Identifier:
22310947
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BORON NITRIDES; DIAMONDS; ELASTICITY; FLEXIBILITY; GRAIN SIZE; HARDENING; HARDNESS; KNOOP HARDNESS; NANOMATERIALS; POLYCRYSTALS; SPECTROSCOPY; SUPPORTS; VICKERS HARDNESS