Microstructure and mechanical properties of Ti/AlTiN/Ti-diamondlike carbon composite coatings on steel
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Alex A. Volinsky Department of Mechanical Engineering, University of South Florida, Tampa, Florida 33620 (Received 10 December 2009; accepted 21 April 2010)
Ti/AlTiN/Ti-diamondlike carbon (DLC) composite coatings were deposited by midfrequency magnetron sputtering and Hall ion source-assisted deposition on high-speed steel W18Cr4V substrates. The coating microstructure and mechanical properties, including hardness, elastic modulus, coefficient of friction, and wear properties were investigated by scanning electron microscopy, Raman spectroscopy, scratch and ball-ondisk friction tests, respectively. Fairly smooth composite coating with strong interfacial adhesion and good mechanical properties was produced. The substrate bias increases sp3 bonds contents in the DLC layer, thus coating hardness increased from 14 to 24 GPa and elastic modulus from 190 to 230 GPa with the increased substrate bias. Adhesion of interfaces between Ti-DLC and AlTiN layer, AlTiN and the steel substrate decreased with the substrate bias. The coefficient of friction is between 0.10 and 0.15, except when the substrate bias is 500 V, it is 0.2. Composite coating wear resistance increased with the substrate bias. I. INTRODUCTION
With the coatings technology development, single layer coatings no longer satisfy industrial performance requirements, thus double or multilayered coatings are being developed as a new generation of protective coatings for cutting tools.1–3 Some of these have already been applied in selected cases in modern machining techniques such as dry high-speed milling, turning, tapping, and drilling, or when minimal lubrication is required. Machining under dry conditions has been accepted to reduce environmental pollution and the high cost of lubricant recycling along with eliminating the need to maintain complicated lubricating systems in modern cutting and milling machines. Such a trend in machining technology has also been influenced by the development of new hard protective coatings for industrial manufacturing, including established low friction coatings, such as diamondlike carbon (DLC).4,5 Amorphous carbon is formed with sp3 and sp2 carbon bonds. If the amount of hydrogen contained in a film is reduced and the ratio of sp3 to sp2 is increased, DLC will usually become harder. DLC coatings are amorphous materials deposited at low temperatures and are very smooth. Although coefficient of friction changes with the measurement conditions, it can be as low as 0.1, or a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0281 J. Mater. Res., Vol. 25, No. 11, Nov 2010
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even less in air,6–9 oil, and water.10 Metal-containing diamondlike carbon (Me-DLC) is a DLC film in which metal nanoclusters are dispersed homogeneously, providing a possibility of solving adhesion problems. Metal clusters are remarkably effective for decreasing stress in DLC films. Tribological properties of the Me-DLC in dry sliding wear using a ball-on-disk t
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