Hardness of Polycrystalline Wurtzite Boron Nitride (wBN) Compacts

Abstract

Wurtzite boron nitride (wBN), due to its superior properties and many potential practical and scientific applications, such as ideal machining/cutting/milling ferrous and carbide materials, especially as an ideal dielectric substrate material for optical, electronic, and 2-D graphene-based devices, has recently attracted much attention from both academic and industrial fields. Despite decades of research, there is an ongoing debate about if the single-phase wBN is harder than diamond because of the difficulty to make pure wBN material. Here we report the successful synthesis of pure single-phase polycrystalline wurtzite-type boron nitride (wBN) bulk material by using wBN powder as a starting material with a well-controlled process under ultra-high pressure and high temperature. The cubic boron nitride (cBN) was also successfully prepared for the first time from wBN starting material for comparison and verification. The X-ray diffraction (XRD) and TEM clearly confirmed that a pure single-phase wBN compact was produced. The microstructure and mechanical properties including Vickers hardness, fracture toughness, and thermal stability for the pure single-phase wBN was first evaluated.

From 2-D to 0-D Boron Nitride Materials, The Next Challenge

“…Nevertheless, C 2 -BN nanocomposites (c-BN: diamond, 1:2) can reach a very high hardness, H V = 85 GPa. More recently, w-BN displayed interesting hardness properties, comparable with the other allotropes [5]. Pure w-BN, treated at a pressure of 10–20 GPa and high temperature (400–1900 °C) reached a hardness as high as H V = 46 GPa.…”

“…Boron nitride (BN) is a chemically stable material exhibiting four different polymorphs: hexagonal (h-BN), cubic (c-BN), rhombohedral (r-BN), and wurtzite (w-BN) [1,2,3,4,5]. The different BN allotropes have attracted considerable interest as a possible alternative to diamond for their great hardness and high thermal stability [3,4,5,6]. Despite a thermal stability higher than diamond (1473 K) and a low reactivity with steel, c-BN still presents a more moderate hardness in comparison with diamond (H V = 40–60 GPa) [3].…”

Bias-Enhanced Formation of Metastable and Multiphase Boron Nitride Coating in Microwave Plasma Chemical Vapor Deposition

“…To get better visualization, high resolution XRD was performed at 2θ of 40–50°. The broad peak at 41–45° was resolved into two peaks which corresponds to w -BN (002) and c -BN (111) [ 15 , 42 , 49 , 50 , 51 ].…”

Applications of Polycrystalline Diamond (PCD) Materials in Oil and Gas Industry

“…Please refer to the reference [12] for more details in NPD development and their performance. In a combination of multi-stage loading, for the first time a two-stage loading device that is integrated directly into the first six-sided cubic pressure chamber was developed [16], eliminating the intermediate conversion process of loading by a single axis. Compared to type 2-6-8 loading based on belt press technology, tri-axial loading significantly improves the transmission efficiency of loads.…”