In the arena of superhard materials, diamond reigns supreme as the undisputed “King of Hardness.” Closely following is cubic boron nitride (cBN), whose unique performance advantages are sparking a “hard-core revolution” across industrial applications.
From a crystalline structure perspective, the atomic arrangement of cubic boron nitride single crystals closely resembles that of diamond—boron atoms and nitrogen atoms form a face-centered cubic lattice through sp³ hybridization, interlocking along diagonals with a 1/4 offset to create a dense covalent bond network. This structure endows it with exceptional hardness metrics: a Mohs hardness of 9.7 and a Vickers hardness ranging from 7000 to 9000 HV. Some nanocrystals even surpass 108 GPa in Vickers hardness, far exceeding traditional abrasives like silicon carbide and aluminum oxide. Despite exhibiting anisotropy in crystal orientation, it already meets the machining demands for most high-hardness materials.
The “hard core” of cubic boron nitride single crystals extends beyond numerical values to their exceptional stability in high-temperature environments. It maintains high hardness and mechanical properties at cutting temperatures exceeding 1200°C, shows no oxidation at 1000°C, and boasts a thermal conductivity of 79.54 W/m·K—several times that of cemented carbide. This characteristic enables it to achieve a metal removal rate 10 times that of diamond when machining ferrous metals like quenched steel and chilled cast iron, effectively solving the challenge of processing hard and tough materials. For instance, in automotive gear machining, cubic boron nitride tools can boost grinding efficiency by 40% and extend grinding wheel life by more than three times.
Chemical inertness is another major advantage of cubic boron nitride single crystals. They exhibit significant inertness toward iron-group elements and their alloys, remain stable in neutral or reducing gases, and resist corrosion in acidic or alkaline environments. This property eliminates the tendency for diamond tools to stick to ferrous materials during machining, making them particularly suitable for “turning instead of grinding” processes in precision components like automotive cylinder liners and bearing steels. A domestic automaker achieved a surface roughness of Ra ≤ 0.8 μm when machining hardened steel (60–62 HRC) using polycrystalline cubic boron nitride tools, with tool life exceeding 1,000 parts—significantly boosting production efficiency.
From single-crystal abrasives to polycrystalline tools, cubic boron nitride single crystals are reshaping modern manufacturing paradigms with their golden combination of hardness, stability, and chemical inertness. In CNC machine tools and automated machining, it has become a key material for achieving high-precision, high-efficiency, and low-pollution processing, propelling manufacturing toward cleaner and smarter production.
