The base material, or substrate, for most thin-film coated-diamond inserts is tungsten carbide (grade C-2). It's basically the same substrate material used for many carbide inserts coated with titanium nitride or titanium carbide.
A carbide insert is made from two main ingredients, carbide and cobalt, which are mixed together in various ratios and sintered. Carbide manufacturers guard their ratios and sintering process details the way chefs protect their recipes.
The carbide used in an insert is granular, although individual grains are very smallmany formulas call for grains in the single-digit micron range. By using different grain sizes specific cutting performance can be selected. For diamond coatings to adhere more firmly to the substrate, a larger grain carbide is usually specified so the surface has some roughness.
Cobalt is the "cement" that bonds the carbide grains. It gives the carbide its cutting characteristics of hardness and toughness.
The mixture of carbide and cobalt is pressed in a mold, giving it the shape of an insert. Chipbreakers and other performance enhancing bumps and valley are formed as part of the molding process. These pressings are then sintered. At high temperature, the cobalt flows around the carbide grains creating a strong and very hard bond.
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