Preparation of superhard cubic boron nitride sintered from commercially available submicron powders

Abstract

Using submicron cubic boron nitride (cBN) powder as a starting material, polycrystalline cBN (PcBN) samples without additives were sintered from 8.0–14.0 GPa at 1750 °C, and their sintering behaviour and mechanical properties were investigated. Transmission electron microscopy analysis showed that high-density nanotwins could be generated from common submicron cBN grains during high pressure and high temperature treatment. The dislocation glide and (111) mechanical micro-twinning are the main mechanisms that underlie plastic deformation in the sintering process, and this contributes to the grain refinement. A refinement in the grain size (∼120 nm), micro-defect (nanotwin and stacking faults), and strong covalent bonding between the grains are crucial for improving the sample mechanical properties. The PcBN sintered at 11.0 GPa/1750 °C possessed outstanding mechanical properties, including a high Vickers hardness (∼72 GPa), fracture toughness (∼12.4 MPam1/2), and thermal stability (∼1273 °C in air).

Polycrystalline cubic boron nitride prepared with cubic-hexagonal boron nitride under high pressure and high temperature

“…Compared with submicron cBN which was synthesized from pure cBN, we find that this submicron cBN synthesized from the special mixture of cBN and hBN precursor presented a large number of defects. [7] This may be attributed to the volume changes of grain which can cause numerous microstructural differences, during the reconstructive phase transition from hBN to cBN. [30] In particular, in the sintering process, the micro defects in crystallines should be generated during the nucleation and growth of a new phase.…”

“…Therefore, the best way to obtain PcBN with excellent mechanical properties is free from additives, and the perfect additive is the material itself. [7] In order to address this problem, more sintering methods have recently been adopted. For the sintering of PcBN without additives under HPHT treatment, the following two different methods are usually applied.…”

Hardness of Polycrystalline Wurtzite Boron Nitride (wBN) Compacts

“…Hexagonal boron nitride (hBN) is a stable phase at ordinary temperature and pressure 4 , and cubic boron nitride (cBN) and wurtzitic boron nitride (wBN) can be synthesized at high temperature and high pressure 2,5–11 . With regard to the mechanical properties of cBN 12–16 , especially its hardness, about 45–50 GPa 17 , there is a certain amount of information that has been reported, however, almost nothing is known about the mechanical properties of wBN because wurtzite is a metastable phase of BN at all pressures and temperatures 18,19 and it is difficult to prepare a pure phase 20 . Previous studies have shown that the hardness of wBN varies significantly from 24 GPa to 54 GPa 17,18 .…”

Binderless Layered BN Toughened cBN for Ultra-precision Cutting

“…立方氮化硼(cBN)是硬度仅次于金刚石的超硬 材料，且热稳定性和化学稳定性优于金刚石，在超 硬刀具领域中应用广泛 [1][2] 。常用 cBN 刀具材料主 要有两类， 即含粘结剂的聚晶 cBN (PcBN)和无粘结 剂 cBN [3] 。其中，在 5~6 GPa、1300~1400 ℃的条件 下采用微米尺寸的 cBN 颗粒与金属或陶瓷粘结剂 结合制备 PcBN，但是粘结剂降低了材料的硬度和 耐磨性，使其硬度仅为 27~40 GPa [4][5] 。为了提高 PcBN 的硬度，研究者们以六方氮化硼(hBN)、热解 类六方氮化硼(pBN)或 cBN 粉为原料在压力≥7.7…”

“…GPa 条件下合成了亚微米或纳米晶粒的无粘结剂纯 相 cBN，该类材料的硬度、耐磨性和热传导性均优 于 PcBN 材料 [4,[6][7][8] 。 无粘结剂 cBN 材料优良的机械性能及其在切削 领域广阔的应用前景，近年来无粘结剂 cBN 材料切 削性能的研究备受关注。如 Taniguchi 等 [9] 通过高温 高压(≥7.7 GPa，>2000 ℃)直接烧结 cBN 粉获得了 无粘结剂 cBN 块材，制备成刀具并实现了硬质合金 的精密切削。Fujisaki 等 [10] 采用超细晶粒无粘结剂 cBN 制备刀具，切削出不锈钢镜面，其耐磨性优于 金刚石。Sumiya 等 [7] 以 hBN 和 pBN 为原料通过高 温高压(≥8 GPa，≥2200 ℃)下的相变获得了无粘结 剂 cBN，切削淬硬钢的性能较好。Wang 等 [11][12] 的 研究表明，无粘结剂 cBN 材料在钛合金高速铣削中 的耐磨性高于 PcBN 和聚晶金刚石刀具。另外， Bushlya 等 [13]…”