arXiv subjects

Hiroaki Ohfuji

Publications and source records attributed to Hiroaki Ohfuji.

2 recordsLinked to original sources

arXiv2012

Polycrystalline γ-boron: As hard as polycrystalline cubic boron nitride

The Vickers hardness of polycrystalline γ-B was measured using a diamond indentation method. The elastic properties of polycrystalline γ-B (B=213.9 GPa, G=227.2 GPa, and E=503.3 GPa) were determined using ultrasonic measurement at ambient condition. Under the loading force up to 20 N, our test gave an average Vickers hardness in the asymptotic-hardness region of 30.3 GPa. The average fracture toughness was measured as 4.1MPa m1/2. Additionally, We also measured the hardness and elastic properties of polycrystalline β-B and PcBN for comparison. The hardness and elastic properties for polycrystalline γ-B was found to be very close to that of PcBN. Our results suggest that the polycrystalline γ-B could be a superhard polycrystalline material for industrial applications.

cond-mat.mtrl-sci↗

arXiv2011

Phase relations in boron at pressure up to 18 GPa and temperature up to 2200 °C

The phase relations in boron have been investigated at high pressure and high temperature using a multianvil apparatus, and the quenched sample has been analyzed by x-ray diffraction, Raman spectra and transmission electron microscopy. We demonstrate that γ-B28 can be synthesized over a wide P-T range, and T-B50 is obtained at higher temperatures and similar pressures. The phase boundary of the β-B106, γ-B28 and T-B50 is determined at pressures between 7 and 18 GPa and the temperatures of 500-2200 °C. The results suggest that T-B50 might be an intermediate phase-metastable, formed for kinetic reasons (Ostwald rule) on the way from β-B106 to T-192 and γ-B28 to T-192.

cond-mat.mtrl-sci↗