Grinding cubic boron nitride

The greatest use of cubic boron nitride is as an abrasive under the name Bora2on, in the form of small crystals, 1—500 p.m in si2e. Usually these crystals are incorporated in abrasive wheels and used to grind hard ferrous and nickel-based alloys, ranging from high speed steel tools and chilled cast-iron to gas turbine parts. The extreme hardness of the crystals and their resistance to attack by air and hot metal make the wheels very durable, and close tolerances can be maintained on the workpieces. 

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

Cubic Phase of Boron Nitride c-BN. The cubic phase of boron nitride (c-BN) is one of the hardest materials, second only to diamond and with similar crystal structure. It is the first example of a new material theoretically predicted and then synthesized in laboratory. From automated synthesis a microcrystalline phase of cubic boron nitride is recovered at ambient conditions in a metastable state, providing the basic material for a wide range of cutting and grinding applications. Synthetic polycrystalline diamonds and nitrides are principally used as abrasives but in spite of the greater hardness of diamond, its employment as a superabrasive is limited by a relatively low chemical and thermal stability. Cubic boron nitride, on the contrary, has only half the hardness of diamond but an extremely high thermal stability and inertness. 

Cubic boron nitride is an important materia that is widely used in cutting tools and as grinding, abrasive materials. Both Hu et al. [8] and Cui et al. [9] have synthesized cubic BN via this method. By using the solvothermal metathesis reaction of BBrs and LisN, Cui and co-workers obtained better yield of cubic BN, and the TEM image and the XRD pattern are shown in Fig. 3. Some other metastable non-oxides have also been prepared and reported using solvothermal method, e.g. AIN [10-11] and Si3N4 [12]. 

Grinding and polishing is one of the oldest applications for wide band-gap materials primarily owing to the property of hardness that some of these materials possess (e.g., diamond). SiC and cubic boron nitride, in addition to diamond, have found a commercial market in grinding and polishing, primarily for ferromagnetic materials with high carbon solubility. 

The use of cubic boron nitride and diamond paste for grinding and polishing minimizes contamination by materials that can be mistaken for minerals in the SEM uialysis. The san5>le pellet is then cut parallel to the polished face to reduce its height to about 0.6 cm, mounted on an aluminum stub, and carbon-coated for use in the SEM. 

Grinding with Diamond and Cubic Boron Nitride Abrasives... 

Diamond and cubic boron nitride (CBN) are the two most frequently applied types of abrasives for ultraprecision grinding (Chen et al. 2002). 

Cubic boron nitride (CBN) has superior thermochemical stability compared to diamond. Ultrafine-crystalline CBN (CBN-U) is a special type of CBN, which has a grinding ratio that is eight times higher, and a higher wear resistance than conventional CBN (Chen et al. 2002). For grinding of ferrous components and other materials that react with diamond, cubic boron nitride is the best choice. 

A layer of cubic boron nitride approximately 0.5 mm thick is bonded to a cemented-carbide tip approximately 5 mm thick. The cemented carbide provides a shock-resisting base. This material will machine chilled cast iron and fully hardened steel and still maintain a cutting edge. It is designed to perform most effectively on materials difficult to cut, and in some cases can replace a grinding operation. 

Tools made from polycrystalline p-BN (and y-BN) [63, 64] can be machined by laser irradiation [65]. Dressing of hard boron nitride tools can be done with sintered alumina-metal (Fe, Cu) sticks [66], and burnishing cubic boron nitride sinters can be done against a smooth complementary p-BN surface [76]. On the other hand, AI2O3 grinding wheels can be dressed by P-BN sintered tools [68]. 

Cubic boron nitride does not react with carbide formers such as Fe, Co, Ni, Al, Ta, and B at approximately 1000°C (while diamond does) this is a useful characteristic in machining and grinding applications. However, it reacts with aluminum at 1050°C and with Fe and Ni alloys containing Al above 1250 C.[i ... 

Silicon carbide and alumina still dominate the abrasive industry at the present time. However their performance in the grinding of superalloys, ceramics, reinforced plastics, and other hard materials is generally unsatisfactory. This has led to the development of new abrasives such as synthetic diamond and cubic boron nitride. Cubic boron nitride was first synthesized in 1957 and has been available commercially since the 1970 s. Although not as hard as diamond, c-BN does not react with carbide formers such as Fe, Co. Ni, Al, Ta, and B at 1000 (while diamond does). However, it reacts with aluminum at 1050°C, with Fe and Ni alloys containing Al above 12S0"C, and with water and water-soluble oils.1 1... 

The invention of cBN was actually part of an attempt by GE to develop a material harder than diamond. Of course, cubic boron nitride turned out to be the second hardest known material (Table 9.1). However, cBN is considerably superior to diamond in precisely the two areas where diamond s performance is poor its abrasion resistance with ferrous alloys, such as steels, and its oxidation resistance. The former property enables it to effectively grind steels, nickel-based superalloys, and cast iron, whereas diamond works best with non-metals and nonferrous metals. The oxidation resistance is important in high-temperatme applications in air or a similar oxidizing environment. 

Micron powders of diamond and cBN also occur as by-products of HPHT manufacturing of mesh materials, and have become increasingly important in their own right as their availability increased. Of course, cubic boron nitride micron powder (BMP) did not exist before 1957. Particles smaller than about 50 to 80 /tm are normally considered micron, although there is some overlap with finer sizes of mesh grinding products. It becomes difficult... 

Cubic boron nitride is second in hardness only to diamond. It is used for high-performance tool bits and in special grinding applications. Cubic BN tooling typically outlasts alumina and carbide tooling and is preferred in applications where diamond is not appropriate, such as grinding of ferrous metals. 

Metal bonded wheels are made nearly exclusively with diamond for very severe applications where high mechanical strength is required. Electroplated cubic boron nitride products are also finding applications, especially of very difficult to grind and very hard steels. 

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