CBN

Cubic boron nitride (cBN) is a synthetic polymorph of boron nitride that adopts a cubic crystal structure isostructural to diamond. It is extremely hard and is produced commercially for industrial use. Natural cBN is not known in economically usable quantities, so all practical material is synthetic. cBN is valued for its hardness as well as its chemical stability with ferrous metals at high temperatures.

Production of cBN occurs under high-pressure, high-temperature conditions from hexagonal boron nitride in the presence of a metal solvent or catalyst, commonly cobalt, nickel, or similar systems. It is produced in two main forms: abrasive powders and polycrystalline cubic boron nitride (PCBN) composites in which grains are bound by a metal or ceramic phase to form cutting tools or grinding wheels.

Properties of cBN include exceptional hardness, high thermal conductivity, and chemical inertness toward iron- and steel-group alloys at elevated temperatures. It remains stable at high temperatures in inert or reducing environments and resists oxidation better than diamond. It is also an electrical insulator.

Applications of cBN are dominated by its use as an abrasive and cutting material for machining ferrous metals and alloys, where diamond would react chemically. PCBN tools are used for turning, milling, and grinding steels and cast irons, while cBN powders are employed in grinding wheels and protective coatings to extend tool life and maintain precision.

Limitations include higher cost relative to conventional abrasives and the need for specialized processing, including compatible binders and cooling conditions. Dust from cBN powders can be an irritant, so appropriate safety measures are recommended.

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