Polycrystalline {\gamma}-boron: As hard as polycrystalline cubic boron nitride

TL;DR

This study measures the hardness and elastic properties of polycrystalline gamma-boron, finding it comparable to polycrystalline cubic boron nitride, indicating its potential as a superhard industrial material.

Contribution

The paper provides the first detailed measurement of gamma-boron's hardness and elastic properties, demonstrating its similarity to cubic boron nitride and potential as a superhard material.

Findings

Gamma-boron has a Vickers hardness of 30.3 GPa.

Elastic moduli of gamma-boron are comparable to PcBN.

Gamma-boron shows promise as a superhard industrial material.

Abstract

The Vickers hardness of polycrystalline {\gamma}-B was measured using a diamond indentation method. The elastic properties of polycrystalline {\gamma}-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 {\beta}-B and PcBN for comparison. The hardness and elastic properties for polycrystalline {\gamma}-B was found to be very close to that of PcBN. Our results suggest that the polycrystalline {\gamma}-B could be a superhard polycrystalline material for industrial applications.