Metal Finishing Guide Book


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to environmental influences such as extreme temperature fluctuations or moisture and salt. In addition, automotive coatings must exhibit a certain toughness to make them resistant to mars and scratches. This requires the right balances between hardness and elasticity. A quick differentiation and determination of these coating Figure 8: Weathering rack at Atlas' facility in Florida with properties is possible with the various car body parts. nanoindentation test. Influence from underlying layers or the substrate can be avoided by selecting a sufficiently low maximum load that keeps the penetration depth of the indent below 10% of the coating thickness. At the beginning of the curing process, the clear coats are relatively soft. One of the key features of a nanoindentation tester is a sensitive automated surface detection. As the measured mechanical properties polymers are influenced by rate of loading and unloading, a thermally stable nanoindentation system is also essential. Drift in the depth measurements caused by changes in environmental temperature must be avoided or accounted for. The Martens hardness (HM) and the Martens hardness after creeping (HMCR) are values which specify plastic and elastic properties of the paint coating. The indentation hardness (HIT) considers only the plastic portion of the material deformation. The hardness parameters allow for better understanding of aging, curing, cross-linking, embrittlement through UV radiation, hardness change through temperature influences and the degree of polymerization of the lacquer. One of the most important advantages of the instrumented indentation test is the determination of elastic properties. The indentation modulus (EIT), creep at maximum load (CIT) can be determined using this method and provides information regarding the visco-elastic properties of lacquer coatings. These properties show the ability of the lacquer to resist weather degradation and heal in case of scratches. Nanoindentation on wear-resistant DLC coatings applied to engine components In order to reduce emissions in combustion engines without sacrificing performance, manufacturers are continually working to improve the ability of the moving components (e.g. camshafts, valve lifters, piston rings and gears) to resist abrasion and reduce friction. Protective coatings such as diamond-like carbon (DLC) are increasingly used in such applications. As DLC coatings can have a wide range of hardness depending on the deposition process it is important to measure the fundamental mechanical properties of this hard, low friction coating. Traditional hardness measurements would involve applyFigure 9: DLC-coated engine components. 455

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