The emergence of cubic boron nitride (cBN) has brought great benefits to the processing of hardened iron-group metals and alloys. However, since the synthesis of cBN needs to be achieved under ultra-high pressure and high-temperature conditions, it is very difficult to obtain high-quality large-grained cBN single crystals due to the limitations of the high-pressure device cavity and the difficulties in synthesis technology. Usually, the size of cBN single crystals is less than 0.5mm, and even large single crystals synthesized using the seed-temperature gradient method are only about 3mm in size. Such a small size can only be directly applied to abrasives, grinding wheels, etc. As a cutting tool, the size still needs to be bigger.
Secondly, although cubic boron nitride single crystals are very hard, they are affected by the crystal cleavage structure. In some processing applications, even as grinding wheels, their performance still needs improvement. Under the condition that we cannot manufacture high-toughness single crystals large enough to be applied to cutting tools, can we better solve this problem?
What came into being is the application of cubic boron nitride polycrystals, sintered bodies and composite materials. The emergence of these technologies, firstly, solved the size problem of cBN and was able to produce large cBN materials with particle sizes ranging from 0.5mm to 50mm; secondly, since these materials belong to polycrystalline structures, there is no cleavage problem, which greatly improves the toughness of cBN materials. Because of this, polycrystalline sintered bodies and composite materials technology have been vigorously developed.
Cubic Boron Nitride
What are cBN polycrystalline materials and cBN microcrystals?
The so-called cBN polycrystalline material is an aggregate of many tiny cBN single crystals connected and irregularly orien ted. In addition to the properties of single-crystal materials, it overcomes the anisotropy of single-crystal materials due to the irregular orien tation of single crystals in the aggregate and has better performance than single crystals in terms of toughness.
The cBN microcrystals mentioned here are polycrystalline abrasive grains with a size of 0.1~0.8mm, which are composed of countless submicron single-crystal cBN. In microcrystals, the cleavage planes are randomly orien ted and form a fairly dense structure, which has high hardness and high wear resistance against macroscopic fractures in all directions.
Microcrystalline cubic boron nitride is a new product launched by General Electric Company in the United States in the 1980s. The product brand is Borazon CBN550. Compared with single-crystal cubic boron nitride, this product has the following characteristics:
1) The abrasive grains are composed of countless single-crystal cubic boron nitrides less than 5μm, avoiding the anisotropy of single crystals;
2) The thermal stability can reach 1473K;
3) There are many turning edges, high processing efficiency and high precision;
4) Self-sharpening;
5) Large abrasive grain size;
6) The thermal stability is still not lower than that of single crystal materials, which can reach 1200℃;
7) The multi-angle shape increases the holding force in the product, increases the cutting edge, and is more efficient;
8) The microcrystalline size is larger than that of single crystals, which can exceed 0.5mm, overcoming the limitation of synthesizing large particles of cBN in high-pressure devices.
Cubic Boron Nitride
General Electric Company of the United States compared single crystal and microcrystalline cubic boron nitride. When grinding difficult-to-process alloys such as M-2 and M-T-15, the grinding efficiency of microcrystalline cubic boron nitride is usually twice that of Borazon CBN-ll by selecting appropriate binders and particle sizes.
It is precisely because of the superior properties of single crystals that microcrystalline cBN has been widely used in industrial processing.
When using cBN grinding wheels to grind low-carbon steel, soft alloy steel and tough high-temperature resistant alloy steel, the metal chips produced are longer, wider and thicker than those of cemented carbide. In order to continue cutting, the chips must be cleared, and the grinding wheel must be trimmed. At the same time, due to the presence of these metal chips, the binder in the grinding wheel will be eroded into pits. If these pits are of the same size as the abrasive particles, the abrasive particles will be pulled out of the grinding wheel surface and accelerate the wear of the grinding wheel. If the abrasive particles are reduced in order to avoid the above phenomenon, the grinding efficiency will be greatly reduced, which is economically inappropriate. The emergence and application of cBN microcrystals can properly solve the above problems. This is because, overall, cBN microcrystals have large particle sizes, high grinding efficiency, irregular shapes, and increased holding force. From the perspective of the cBN microcrystal structure, the particle size of each single crystal that makes up the cBN microcrystal is very small, and no long-processing debris will be produced. Each year is also within the smaller scale of the microcrystal. In this way, when using cBN microcrystals to cut the above materials, both high cutting efficiency and long service life are achieved, achieving the best of both worlds.
Microcrystalline cBN also has good thermal properties. There are often residual stresses in cBN single-crystal abrasives. Due to the existence of these stresses, the single crystal breaks when the ambient temperature is about 700°C, which is bound to affect the life of the product. Experiments on microcrystalline cBN show that the toughness of cBN550 abrasive does not decrease after being subjected to a high temperature of 1200°C. This not only increases the service life of the product because the crystal is heat-resistant and not easy to break but also allows the use of high-temperature binders in the production of the product, which is also an important link in improving the service life of the product.
Supplier
TRUNNANO is a globally recognized manufacturer and supplier of compounds with more than 12 years of expertise in the highest quality nanomaterials and other chemicals. The company develops a variety of powder materials and chemicals. Provide OEM service. If you need high quality Boron Nitride BN Powder, please feel free to contact us. You can click on the product to contact us.
