TY - JOUR
T1 - Synthesis of coarse-grain-dispersed nano-polycrystalline cubic boron nitride by direct transformation under ultrahigh pressure
AU - Ichida, Yoshio
AU - Ohfuji, Hiroaki
AU - Irifune, Tetsuo
AU - Kunimoto, Takehiro
AU - Kojima, Yohei
AU - Shinmei, Toru
N1 - Funding Information:
This work was supported by the Joint Usage/Research Center PRIUS (2016-A12), Ehime University. The authors are grateful to Miss N. Uchiyama for preparing the TEM samples and would also like to thank professors K. Fujino, Toru Inoue, Y. Nishihara, T. Ohuchi, M. Nishi, and the members of the Geodynamics Research Center, Ehime University, for their support and useful discussions.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/8
Y1 - 2017/8
N2 - Using a turbostratic pyrolytic boron nitride produced by a chemical vapor deposition process as a starting material, we conducted experiments for synthesizing polycrystalline cubic boron nitride (PcBN) at a temperature of 1600–2600 °C and pressure of 25 GPa with a multi-anvil high-pressure apparatus. Moreover, we evaluated the microstructure and hardness characteristics of the synthesized PcBN. The results showed that a complete single-phase PcBN without residual wurtzite BN was produced at 1900 °C or higher and a nano-polycrystalline cBN (NPcBN) having a mean grain size smaller than 100 nm could be synthesized at a temperature of 1950 °C or lower under a pressure of 25 GPa. Furthermore, we found that a single-phase NPcBN (CGD-NPcBN) having a characteristic microstructure of dispersed relatively coarse grains in a fine polycrystalline structure, which was harder than 53.5 GPa in Knoop hardness, was produced at a temperature range of 1900–1950 °C. In particular, at 1950 °C, CGD-NPcBN having a Knoop hardness of 54.7 GPa, which is 25% higher than that of the hardest binderless PcBN tool currently in practical use, can be synthesized. In addition, we verified that the Knoop hardness of the single-phase PcBN with a uniform microstructure increased with decreasing mean grain size, which complied with the Hall–Petch relationship.
AB - Using a turbostratic pyrolytic boron nitride produced by a chemical vapor deposition process as a starting material, we conducted experiments for synthesizing polycrystalline cubic boron nitride (PcBN) at a temperature of 1600–2600 °C and pressure of 25 GPa with a multi-anvil high-pressure apparatus. Moreover, we evaluated the microstructure and hardness characteristics of the synthesized PcBN. The results showed that a complete single-phase PcBN without residual wurtzite BN was produced at 1900 °C or higher and a nano-polycrystalline cBN (NPcBN) having a mean grain size smaller than 100 nm could be synthesized at a temperature of 1950 °C or lower under a pressure of 25 GPa. Furthermore, we found that a single-phase NPcBN (CGD-NPcBN) having a characteristic microstructure of dispersed relatively coarse grains in a fine polycrystalline structure, which was harder than 53.5 GPa in Knoop hardness, was produced at a temperature range of 1900–1950 °C. In particular, at 1950 °C, CGD-NPcBN having a Knoop hardness of 54.7 GPa, which is 25% higher than that of the hardest binderless PcBN tool currently in practical use, can be synthesized. In addition, we verified that the Knoop hardness of the single-phase PcBN with a uniform microstructure increased with decreasing mean grain size, which complied with the Hall–Petch relationship.
KW - Direct transformation
KW - Grain size
KW - Knoop hardness
KW - Nano-polycrystalline cubic boron nitride
KW - Ultrahigh pressure
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U2 - 10.1016/j.diamond.2017.04.020
DO - 10.1016/j.diamond.2017.04.020
M3 - Article
AN - SCOPUS:85019923535
VL - 77
SP - 25
EP - 34
JO - Diamond and Related Materials
JF - Diamond and Related Materials
SN - 0925-9635
ER -