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21CUTTING MATERIALSNanolayered CoatingsPVD coatings, which were introduced in the late 1980s, performed a gigantic step in overcoming the complex problems that prevented progress within the field of nanotechnology. PVD coatings brought a new class of wear-resistant nanolayered coatings. Such coatings (Fig. 2.5) that are a combination of layers having a thickness of up to 50 nanometers (2 microinch), demonstrate significant increases in the strength of the coating compared to conventional methods.Fig. 2.5.PVD coating of ISCAR%u2019s carbide grade IC807 features a nanolayered structure %u2013 SEM image.Carbide GradeA combination of cemented carbide, coating and post-coating treatment produces a carbide grade. Only one of these components - the cemented carbide, a composite material comprising hard carbide particles that are cemented by binding metal - is the necessary element of the grade. The others are optional. Therefore, the term %u201ccemented carbide%u201d can refer to both the substrate of a coated grade and to an uncoated grade.Coating Bottom LineCoating materials have higher microhardness than tungsten carbide. In cutting tools, introducing coatings has changed a natural relation between hardness and toughness of hard metals. When coated, a tungsten carbide demonstrates higher wear resistance when compared to the uncoated carbide of the same toughness level. Hence, coating facilitates changing physical and mechanical parameters of tungsten carbide, which determine performance data. In addition, coating technology has enabled optimizing cutting capabilities of hard metals to machine specific groups of engineering materials by, for example, improving resistance to abrasion, diffusion, or oxidation. This has resulted in considerable increases in both cutting speed and productivity.Wear resistant coatings have found use in not only carbide tools but other cutting materials. For instance, PVD coated HSS tools are common today.Fig. 2.6. post coating treatmentintermediate layerTiCNTiNsubstrateAl2O3TiCNISCAR%u2019s carbide grade IC6025, which is intended for indexable turning inserts, features multilayer MT CVD coating and post-coating treatment.