Applications of Diamond and cBN

In 1996 Leger et al. [228] reported the synthesis of stishovite from a quartz at 20 GPa and 1100°C and measured a hardness of 33 GPa for the polycrystalline compact produced. As the samples obtained were very small, a maximum load of 1.9 N during hardness testing was possible. Synthesis of this material in larger quantities has not yet been possible. 

Natural and synthetic diamond are complementary, not competing products. While today a minor player, natural industrial diamond still plays an important role in a variety of special applications where one or other of its particular characteristics will make it the preferred material (refer to Section 1.5.5 for some examples). 

Industrial applications of diamond have developed over the years as a result of developments by tool makers, machinery manufacturers and the advert of new materials. In addition, new diamond (and cBN) products have evolved, either as a result of technological advances in synthesis or in response to the requirements of a new application, and it is this multi-partnership relationship within the industry which has resulted in the dramatic growth and diversification since the early 1960s. 

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Section 1.5 summarizes the many and varied applications of diamond and cBN materials. The applications of diamond grown using the CVD technique are discussed in Chapter 2 of Part III. 

Single crystal cBN is not of industrial importance for cutting applications as it offers few benefits over monocrystalline diamond and is intrinsically more difficult to synthesize. As such, all industrial cBN tools are composite materials prepared using powder metallurgical techniques, but sintered under similar conditions to those used for the synthesis of diamond and cBN from their softer allotropes (graphite in the case of diamond). 

Moriguchi, H., Tsuzuki, K., Itozaki, H., Ikegaya, A., Hagiwara, K., Takasaki, M., Yanase, Y., Fukuhara, T., (2001), Fabrication and applications of high-toughness, highly wear-resistant diamond-and cBN-dispersed cemented carbide , Sei Technical Review, 51, 121-125. 

Human fascination with diamond as a hard gemstone dates back several millennia, while the use of diamond for industrial manufacturing and processing is much more recent and has grown considerably since the development of high-pressure/high-temperature (HPHT) methods for synthesis of diamond and cubic boron nitride (cBN). After a brief historical overview, this chapter will describe the industrial diamond and cBN products in widespread use today and the applications for which they are so well suited ... 

Diamond and cBN powders produced by milling are essentially monocrystalline and dominate the market. However, polycrystalline diamond powder can also be produced by shock synthesis. Under suitable conditions, shock waves produced by explosively driven projectiles can produce HPHT conditions in confined volumes for a sufficient duration to achieve partial conversion of graphite into nanometer-sized diamond grains which can also sinter into micrometer-sized, polycrystalline partieles." This process was commercialized by DuPont to produce a polycrystalline DMP (trade name Mypolex ) that is more friable than monocrystalline DMP and is well suited to fine polishing applications. Hexagonal (graphite-hke) BN will also react under shock-synthesis conditions, but the dense, nanometersized particles that are produced are of the wurtzite phase (wBN) rather than the cubic phase. So far, nano-wBN has not achieved much commercial importance. 

Both the demands for advanced grinding tools and for the precise machining of hard cast iron and hardened steel with cutting ceramics are expected to promote the further development of powder technologies for the manufacture of highly perfect submicrometer microstructures for applications in fields where diamond or cBN tools are too expensive. 

Boron nitride is an entirely synthetic material (with no natural occurrence) and the cubic crystal structure is synthesized from the softer hexagonal (HBN) aUotrope using ultrahigh pressures as in the case of diamond. CBN crystals exhibit less than half the hardness of diamond, but there are no industrial applications for such materials. Instead, aU industrially relevant materials are polycrystal-Une in nature, produced by sintering micron cBN... 

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