The properties of cubic boron nitride (CBN for short) are similar to those of diamond, and some properties,
such as thermal stability, are better than diamond. Therefore, it has as wide a range of applications as diamond.
The hardness of a substance is related to the atomic spacing of the constituent lattice, and as the atomic spacing decreases, the crystal hardness increases. CBN is 1.57 angstroms, and the shortest distance between diamond atoms is 1.5 angstroms. Therefore, the hardness of CBN (microhardness 71.54GPa) is slightly lower than that of diamond, but higher than that of the other two main abrasives, silicon carbide (microhardness 25.48~35.28 GPa) and alumina (microhardness 17.64~27.44GPa) are much higher.
Using a Knoop hardness tester, the hardness of CBN single crystal in the  direction is 4600kg/mm2, while that of diamond is 10000kg/mm2; the hardness of CBN single crystal in the  direction is 3200kg/mm2, while that of diamond is 7000kg/mm2, This shows that the hardness of CBN is anisotropic, and its hardness is slightly lower than that of diamond.
The superhard materials currently used in production mainly refer to diamond and cubic boron nitride. The common feature of cubic boron nitride and cubic diamond is that the "bond angle" of the covalent bond in their structure is 109°28'. It is this 109°28' covalent bond angle that makes cubic boron nitride and cubic diamond have the highest hardness and is called superhard material.
2. Thermal conductivity
Cubic boron nitride has good thermal conductivity, its thermal conductivity (79.54w/m﹒k), although not as good as diamond (146.5w/m﹒k), but much higher than high-speed steel (16.7~25.1w/m﹒k) ) and cemented carbide (20. 33 ~80.77 w/m﹒k). With the increase of cutting speed, the thermal conductivity of CBN gradually increases, which is beneficial to reduce the temperature of the cutting zone and reduce the diffusion wear.
At the same time, due to the good thermal conductivity of CBN, it is second only to diamond as a heat sink.
3. Thermal stability and oxidation resistance
Cubic boron nitride has high thermal stability and can withstand cutting temperatures above 1200 ° C, which is better than diamond. Cubic boron nitride has high hardness and high thermal stability (referred to as high thermal hardness), and can be used as a high temperature resistant material to reduce thermal damage to materials (tools).
The heat resistance of cubic boron nitride is mainly determined by its composition and structure. Although cubic boron nitride has a similar structure to diamond, the carbon atoms on the diamond surface are unsaturated. Under high temperature (above 720°C), these unsaturated surface carbon atoms are easily combined with oxygen atoms to form carbon oxides. Escape the crystal, so that the crystal gradually peels off and disintegrates. The surface of the cubic boron nitride crystal is covered by nitrogen and boron atoms, and the electronic layer structure of the boron atom is 1S22S22P1, which can provide three bonding electrons, so that the valence bond of the boron atom on the crystal surface is saturated without dangling bonds, so It is still relatively thermally stable at the diamond oxidation temperature.
Therefore, CBN has high anti-oxidation ability, and no oxidation phenomenon occurs at 1000 °C. In vacuum, the phase transition from CBN to HBN occurs when the temperature reaches 1550 °C.
4. Chemically inert
The chemical properties of cubic boron nitride are very large, and it has high chemical stability to acids and alkalis in neutral and reducing gas media.
CBN is also chemically resistant to iron, steel and oxidizing environments, forming a thin layer of boron oxide when oxidized. This oxide provides chemical stability to the coating, so it is especially suitable for processing ferrous materials. On the other hand, diamond is not the case. Steel and iron have a large affinity for carbon, so it is easy to stick chips during grinding, resulting in poor grinding effect.
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