The extreme hardness of diamond, coupled to its wear resistance, makes it an ideal candidate for use in cutting tools for machining non-ferrous metals, plastics, chip-board and composite materials. Indeed, industrial diamond has been used for this purpose since the 1960s, and remains a lucrative commercial process today. This involves either gluing the diamond grit to a suitable tool (saw blades, lathe tools, drill bits), or consolidating the diamond grit with a suitable binder phase (e.g. cobalt or silicon carbide) to make a hard, tough and durable composite. CVD
diamond is beginning to be used in a similar way, by coating the diamond directly onto the surface of the tungsten carbide tool pieces. Initial tests indicate that such CVD diamond-coated tools have a longer life, cut faster, and provide a better finish than conventional tungsten carbide tools. However, the term non-ferrous should be emphasised here, since this highlights one disadvantage that diamond has over other tool materials - it reacts with iron at high temperatures, and so cannot be used to cut ferrous materials such as steel. However, some of the newer composite metals that are beginning to be used in the aerospace and automobile industries, such as aluminium-silicon alloys, are excellent candidates for diamond-coated cutting tools, as they are very difficult to machine with conventional materials.
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