Diamond-coated products

The first products with diamond films are already on the market. Audiophiles can buy tweeters that have diaphragms coated with a thin diamond film that limits sound distortion. Watches with diamond-coated crystals are planned, as are diamond-coated windows in infrared scanning devices used in analytical instruments and missile guidance systems. These applications represent only the beginning for diamond-coated products. ... 

The activated CVD diamond techniques can be mote attractive in cases where the huge capital investment (several hundred million dollars) requited for the HP—HT technology is not available or where the high level of technical knowledge requited for HP—HT synthesis is not available. In addition, most wear-resistant apphcations requite diamond coatings only of the order of a few micrometers thick. Such coatings can be deposited ditecdy on the finished product without the need for further finishing if CVD techniques are employed. 

Further improvements in deposition technology are still needed—only substrates stable at a temperature of 1000°C can be coated at present—but the time may not be too far off before diamond coatings on a variety of consumer products become commonplace. 

Methane high-temperature, in-situ cracking to carbon and easily disposed of gaseous by products is practiced in the carbon/graphite composites industry where additional layerings of amorphous or microstructured carbon deposits are fabricated on preformed scaffolds. These are utilized primarily in the aerospace industry. Thin diamond coatings are also fabricated by the low-vacuum, in-situ chemical vapor deposition from methane decomposition. 

The primary goal of this chapter is to provide an overview of the recent developments in the production and uses of diamond coatings for tribological applications. A brief description of the friction and wear mechanisms of diamond in general and diamond coatings in particular will be presented first. This will be followed by a... 

Several companies are engaged in the production of CVD-diamond-coated tool inserts. DeBeers, Mitsubishi, Nachi-Fujikoshi, Norton, Kennametal, Sandvik, and Sumitomo are the major firms. Kennametal and Sandvik provide diamond-coated tools on a commercial basis. Based on the input of several tool insert manufacturers, the estimated world market for diamond-coated inserts is 10 to 20 million per year. As discussed above, CVD- diamond-coated inserts are primarily targeted for machining... 

Not included in the production figures in Table 5.7-1, is the production of in-situ produced diamond coatings by gas phase pyrolysis (chemical vapor deposition, CVD), which are acquiring increasing industrial importance. The worldwide market for diamond-like- and CBN-coatings (CBN =cubic boron nitride) had a volume in 1993 of 40 million US, with an annual growth rate to 1998 of 30 to 40%. 

Since that time, synthetic diamond films have developed into an important high-tech product employed for many purposes. In comparison to other forms of diamond, the most attractive difference is the facile generation of diamond coated workpieces in almost any desired shape. The preparation of thin layers, for example, for electronic applications, became possible as well only after the development of CVD methods. 

Owing to remarkable mechanical properties Hke great hardness, scratch resistance and a low frictional coefficient in combination with a high tolerance for aggressive environmental conditions, diamond-coated objects have been developed soon after the first preparation of diamond films. Today the respective products are employed in many technical apphcations. 

Figure 13 Sharpened, diamond-coated silicon whisker. Product bulletin, Containerless Research Inc., Evanston, IL., with permission from Dr. P. C. Nordine, President.

Abrasive appHcations for industrial diamonds include thek use in rock drilling, as tools for dressing and tmeing abrasive wheels, in polishing and cutting operations (as a loose powder), and as abrasive grits in bonded wheels and coated abrasive products. 

The bulk of synthetic industrial diamond production consists of the smaller crystal sizes up to 0.7-mm particle size (25 mesh). This size range has wide utihty in industry, and a significant fraction of the world s need for diamond abrasive grit is now met by synthetic production yielding thousands of kilograms per year. Because the raw materials are plentiful, synthetic production could, if necessary, supply the world demand for diamond abrasive. Development work continues in order to improve size and utility of the manufactured product and to realize the full potential of diamonds at minimum cost. An appreciable increase in performance has been obtained by coating the diamonds with a thin layer of nickel or copper, before incorporating them into wheels. The thin layer of metal apparendy improves adhesion and heat transfer. 

DLC coatings are already in production in several areas (optical and IR windows) and appear particularly well-suited for abrasion and wear applications due to their high hardness and low coefficient of friction. They have an extremely smooth surface and can be deposited with little restriction of geometry and size (as opposed to CVD diamond). These are important advantages and DLC coatings will compete actively with existing hard coatings, such as titanium carbide, titanium nitride, and other thin film... 

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