Campus Units

Aerospace Engineering, Materials Science and Engineering, Mechanical Engineering, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

2012

Journal or Book Title

Proceedings of the National Academy of Sciences

Volume

109

Issue

47

First Page

19108

Last Page

19112

DOI

10.1073/pnas.1214976109

Abstract

Disordered structures of boron nitride (BN), graphite, boron carbide (BC), and boron carbon nitride (BCN) systems are considered important precursor materials for synthesis of superhard phases in these systems. However, phase transformation of such materials can be achieved only at extreme pressure–temperature conditions, which is irrelevant to industrial applications. Here, the phase transition from disordered nanocrystalline hexagonal (h)BN to superhard wurtzitic (w)BN was found at room temperature under a pressure of 6.7 GPa after applying large plastic shear in a rotational diamond anvil cell (RDAC) monitored by in situ synchrotron X-ray diffraction (XRD) measurements. However, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN but probably underwent a reversible transformation to a high-pressure disordered phase with closed-packed buckled layers. The current phase-transition pressure is the lowest among all reported direct-phase transitions from hBN to wBN at room temperature. Usually, large plastic straining leads to disordering and amorphization; here, in contrast, highly disordered hBN transformed to crystalline wBN. The mechanisms of strain-induced phase transformation and the reasons for such a low transformation pressure are discussed. Our results demonstrate a potential of low pressure–room temperature synthesis of superhard materials under plastic shear from disordered or amorphous precursors. They also open a pathway of phase transformation of nanocrystalline materials and materials with disordered and amorphous structures under extensive shear.

Comments

This article is published as Ji, Cheng, Valery I. Levitas, Hongyang Zhu, Jharna Chaudhuri, Archis Marathe, and Yanzhang Ma. "Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure." Proceedings of the National Academy of Sciences 109, no. 47 (2012): 19108-19112. 10.1073/pnas.1214976109. Posted with permission.

Copyright Owner

The Authors

Language

en

File Format

application/pdf

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