Diamond Coated Cutting Tools

A wide range of cutting-tool materials is available. Properties, performance capabilities, and cost vary widely (2,7). Various steels (see Steel) cast cobalt alloys (see Cobalt and cobalt alloys) cemented, cast, and coated carbides (qv) ceramics (qv), sintered polycrystalline cubic boron nitride (cBN) (see Boron compounds) and sintered polycrystalline diamond tbin diamond coatings on cemented carbides and ceramics and single-crystal natural diamond (see Carbon) are all used as tool materials. Most tool materials used in the 1990s were developed during the twentieth century. The tool materials of the 1990s... 

Fig. 14. A scanning electron micrograph of a diamond coating on a siUcon nitride cutting tool (b) at higher magnification, the octahedral growth of...

Another approach is to coat the cutting tool material with a carbide former, such as titanium or siUcon or their respective carbides by CVD and deposit diamond on top of it. The carbide layer may serve as an iaterface between diamond and the cemented carbide, thus promoting good bonding. Yet another method to obtain adherent diamond coatings is laser-iaduced microwave CVD. By ablating the surface of the substrate with a laser (typically, ArF excimer laser) and coating this surface with diamond by microwave CVD, it is possible to improve the adhesion between the tool and the substrate. Partial success has been achieved ia this direction by many of these techniques. 

Oles, E. J., et al., The New Diamond-Coated Carbide Cutting Tools, Diamond Conference, Barcelona, Spain (Sept., 1995)... 

One of such unique coatings is Diamond Like Carbon (DLC). The conventional synthesis of synthetic diamonds requires extremely high temperatures and pressures. By PECVD, Diamond Like Carbon is created under mild conditions by the decomposition of methane in H2/CH4 mixture. The applications of DLC are numerous coatings for cutting tools, optical fibres, electronic devices for reading magnetic tapes, or even protective coatings in chemical reactors. 

The surface properties of many systems can be significantly improved by the use of coating exhibiting specific characteristics. Because of their outstanding properties, diamond films are involved in the coating of many products, such as cutting tools, optical items (disks, lenses, windows), biological implants. 

Some of the present industrial uses of diamond coatings include cutting tools, optical windows, heat spreaders, acoustic wave filters, flat-panel displays, photomultiplier and microwave power tubes, night vision devices, and sensors. Because its thermal conductivity and electrical insulation qualities are high, diamond is used for heat sinks in x- ray windows, circuit packaging, and high-power electroific devices. Moreover, the high chemical stability and inertness of diamond make it ideal for use in corrosive environments and in prosthetic devices that require biocompatibility. 

Fig. 11 Morphology of cutting edge of diamond-coated tool insert.

Diamond-coated tools are primarily used in the machining of nonferrous metals, alloys, and composite materials that are inherently very difficult to cut or machine. The range of materials that are suitable for machining by diamond-coated tools include aluminum and its alloys (in particular high-silicon aluminum alloys) magnesium audits alloys copper, lead, and manganese alloys graphite carbon plastics ... 

Fig. 14 Cutting performance of uncoated, PCD and CVD-diamond-coated tool inserts while milling graphite. ...

Diamond Coating for cutting tools, coatings for wear resistance, optical coatings, semiconductor devices. 

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