Researchers at Sichauan University, China, University of Nevada, USA, and the Chinese Academy of Sciences, China, have published work on the combination of diamond and cubic boron nitride to form a new superhard material suitable for cutting tool applications.
Diamond and cubic boron nitride (cBN) as conventional superhard materials have found widespread industrial applications, but both have inherent limitations. Diamond is not suitable for high-speed cutting of ferrous materials due to its poor chemical inertness, while cBN is only about half as hard as diamond.
Because of their affinity in structural lattices and covalent bonding character, state the authors of the paper, diamond and cBN could form alloys that can potentially fill the performance gap. However, the idea has never been demonstrated because samples obtained in the previous studies were too small to be tested for their practical performance.
The paper, Diamond-cBN alloy: A universal cutting material (http://scitation.aip.org/content/aip/journal/apl/107/10/10.1063/1.4929728), published in Applied Physics Letters, reports the synthesis and characterisation of transparent bulk diamond-cBN alloy compacts whose diameters (3 mm) are sufficiently large for them to be processed into cutting tools. The testing results show that the diamond-cBN alloy has superior chemical inertness over polycrystalline diamond and higher hardness than single crystal cBN. High-speed cutting tests on hardened steel and granite suggest that diamond-cBN alloy is indeed a universal cutting material.
The researchers tested the cutting performances of the alloy on hardened steel and granite bars on a CNC lathe. They found that the diamond-cBN alloy rivalled polycrystalline cubic boron nitride’s wear and tool life on the steel samples and exhibited significantly less wear when cutting through granite. The alloy also demonstrated a more preferable high-speed cutting performance than either polycrystalline CBN or commercial polycrystalline diamonds.
Future work for the team involves developing synthesis technology for centimetre sized diamond-cBN alloy bulks to bring the process up to industrial-scale production.