Diamonds are forever, except when they oxidize while cutting through iron, cobalt, nickel, chromium, or vanadium at high temperatures. Conversely, cubic boron nitride possesses superior chemical inertness but only about half of the hardness of diamonds. In an attempt to create a superhard material better suited for a wide variety of materials on an industrial scale, researchers at Sichuan University, China, created an alloy composed of diamonds and cubic boron nitride (cBN) that boasts the benefits of both.
“Diamond and cubic boron nitride could readily form alloys that can potentially fill the performance gap because of their affinity in structure lattices and covalent bonding character,” says Duanwei He, a professor at Sichauan University. “However, the idea has never been demonstrated because samples obtained in previous studies are too small to test their practical performance.”
To synthesize diamond-cBN alloys, researchers subjected a homogenous mixture of diamond and cubic boron nitride powder to a vacuum furnace at 1300 K for two hours, then pressed the material into 3.5 mm pellets under pressure greater than 15 GPa and temperatures above 2000 K. The pellets were then polished and sharpened into cutting implements.
The cutting performances of the alloy were then tested on hardened steel and granite bars on a computer numerical controlled lathe. The diamond-cBN alloy rivaled polycrystalline cubic boron nitride’s wear and tool life on the steel samples, and exhibited significantly less wear when cutting through granite. A more preferable high-speed cutting performance than either polycrystalline CBN or commercial polycrystalline diamonds was also found.
Future work for He and his colleagues involves developing synthesis technology for centimeter-sized diamond-cBN alloy bulks to bring the process up to industrial-scale production.
Image caption —Bulk diamond-cBN alloy samples synthesized at 20 GPa/2200°C with a diameter of ~3 mm, over a copper screen to exhibit its transparency (a, b). Polished rake faces of diamond-cBN alloy cutters (c, d).
