Cubic boron nitride is being characterized by a unique combination of physical-mechanical and chemical properties. Disposition of atoms in crystal grate belongs to the structural type of spharelite, which determine high density and hardness of crystals CBN. (Fig.1). As a result of breaking away crystals along the shear plane, i.e. breaking of atomic bonding, at grinding cutting edges of CBN crystals permanently renew, due to this is reached high and stable cutting ability. (Fig.2)

Combination of high toughness and heat resistance enables using high speeds of grinding at CBN tools. Owing to high hardness and low coefficient of friction grinding of high-speed steel with CBN tool is made with high-performance and quality result, without phase and structural changes in surface layer.

Mechanical toughness of CBN grains depends on perfection of internal structure and isometrics of grains. Modulus of elasticity of CBN (706 GPa) is significantly bigger than that of regular abrasives (296-365 GPa).

CBN products

Specific heat of CBN (670 J/kg·°C) is low than that of electrocorundum. Coefficient of linear thermal expansion of CBN is 1,5 -3 times lower than that of electrocorundum. That is why grains of cubic boron nitride have lower thermal deformation.

Chemical passivity at interaction with metals is an importantproperty of CBN, as opposed to diamond and silicon carbide it is inactive to iron, the basics of metals and iron-carbon alloy, which lowers diffusive and adhesive deterioration of grain. This excludes its gripping at interaction with treated materials, makes lower the grinding force and temperature. Crystals of CBN do not lose their cutting properties, phase structure and toughness till the temperature 1100-1200C°. Moreover, at temperatures of active oxidation the strength of grains is increasing, as grains are ovalized and appearing on them layers of boric anhydride B2O3 are cementing defects of surface. Formation of B2O3 layer on grains of cubic boron nitride hampers diffusion of oxygen. Obvious oxidation of CBN crystals starts at heating temperature more than 1200°C.

Thus, cubic boron nitride significantly supersedes toughness, endurance, abrasive ability, thermal conductivity and chemical stability of standard abrasive materials (electrocorundum, SiC), i.e. all parameters determining quality and efficiency of instrumental abrasive materials.

Depending on conditions of growth, composition and properties of crystallization environment, synthesized CBN appears to be aggregates, druses of recrystallization, growth twins and monocrystals of different degree of crystal perfection.

Forms of CBN crystals.


Electroless nickel coating

Durability and efficiency of abrasive tools is significantly dependant on firmness of grain strengthening in bond. That is why high adhesive characteristics of contact - "abrasive-bonding material", increases tool performance effectiveness.

Due to advanced surface of elecroless nickel coating, CBN crystals are well knit with bonds, which ensures firm retention of grains before complete deterioration during abrasive tool performance. During the electroless nickel cladding process, the surface of crystal is catalytically activated, thus the optimum adhesion between CBN and nickel is reached.

Thermal conductivity of uncoated CBN, equaling 41,9 Wt/(m·°C) is from 2 up to 4 times higher than that in regular abrasives. It provides intensive heat deflection, emergent from working surface of CBN grains during grinding process, while the coating of crystal itself aids to distribute temperature farther on the bond, which lowers general temperature of grinding. Thus suggested coating significantly betters thermo-physical properties of tool.

x3500

CBN H600 60N

x350

x1000

x2500


Heat resistance


Main operational characteristics of abrasive instrumental materials is heat resistance - ability of materials to retain mechanical characteristics and structure upon multiple thermal disturbances. High heat resistance is ensured with, from one hand substance properties - low rate of coefficient of thermal expansion and modulus of elasticity, high rate of thermal conductivity, and, from the other hand, for its value affects the degree of perfection of crystal structure, number of impurities and defectiveness of material.

The degree of thermal stability is being evaluated as a result of comparison of basic mechanical hardness of crystals and corresponding hardness after thermal treatment, including heating, isothermal exposure and cooling. Thermal treatment is made in hydrogen environment at 1200°C and time of thermal exposure makes 20 minutes.

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All pictures and technical data used in this brochure are property of Haris Division. Unauthorized duplication is a violation of copyright law.

All pictures and technical data used in this brochure are property of Haris Division. Unauthorized duplication is a violation of copyright law.