Overview of PVD Coating Development and Coating Properties<\/p>\r\nThe last decades, advances in coating deposition technologies have led to the development of nano-structured coating materials with unique properties, such as superhardness (defined as hardness H>40 GPa) in combination with high toughness. Coatings prepared by plasma assisted deposition are often known to exhibit increased hardness compared to their corresponding bulk counterparts, due to factors such as grain size refinement, high growth-defect density and residual compressive stress, induced by the deposition process.\r\n\r\nAs the demand for PVD coating grows, it becomes increasingly apparent that the single element coatings are not capable to meet the requirements of the diverse applications of modern day machinery. PVD coating industry is constantly evolving to meeting the manufacturing demands, it has shifted from general purpose binary nitride coatings, to engineered multi-elements, Quaternary coatings for specific conditions, and it is now favoring the superlattice coatings, that are comprised of multi-elements, components, and nanometer scaled layered\/hbrid structures,\r\n\r\nThe engineered coatings incorporate numerous thin films, comprised of a unique coating system, which yields superior tribological properties. The selection of the various phases of such coating processes and the “blueprint” in which they are presented provides an important control parameter. In addition, many applications require that the coating process operates at a multi-functional mode, such as coupling temperature and oxidation resistance, while providing a low coefficient of friction under adverse conditions. Often times, these mechanical, chemical and physical demands cannot be met with monolithic thin film.\r\n\r\nPVD coating<\/b>\u00a0uses multi-component (layered) coatings arranged in specific designs to provide the properties needed. These coating systems typically comprise of the following layers:\r\n\r\n-An adhesion layer that ensures the bonding between the substrate and the coating system\r\n\r\n-An intermediate layer that supports the synergy between the adhesion layer and the outer functional layer\r\n\r\n-A functional layer possesses favorable properties on contact with the working component and environment\r\n\r\nUsually these three layers are applied by different PVD methods, depending upon specific needs and requirements. By filtering through the advantages and disadvantages of each coating method, choosing an appropriate coating selection, and incorporating different levels of ion bombardment energy through bias control we are able to come up with the optimal surface coating.\r\n\r\nThere are also methods to combat the complexity of the multilayer deposition, by offering multi-element, monolith layer coating. This method offer better coating process control than the multi-layer deposition. Instead of igniting many element targets in systematic way, several alloyed targets are able to achieve the same task.\r\n\r\nThin hard PVD coatings are today frequently used in order to improve the tribological performance of forming tools, cutting tools, and machine elements. In all these applications the surface roughness of the coated part is of utmost importance since it will affect the friction, wear and fatigue characteristic of the tribo-system. Since most PVD coatings are significantly harder than the counter surface material a high coating surface roughness will result in a high wear rate of the counter surface. In general, a high coefficient of friction is due to a significant contribution from the ploughing component of friction because protruding surface asperities (macroparticles, etc.) of the harder rough coating surface will also increase the material pick-up tendency which may cause problems such as galling in metal forming application. A pronounced surface roughness will also increase the tendency to crack initiation and surface fatigue of the coated part due to high contact stresses at the asperities. Finally, a rough substrate surface may also result in problems related to poor adhesion, i.e. coating spalling. In order to reduce these problems, PVD coatings of less hard materials such as diamond like carbon and carbon rich metal carbide based structures can be used. These coatings are gentler to the counter surface and show a beneficial friction coefficient towards many engineering materials also under dry sliding conditions. The mechanisms controlling the low friction properties of these coatings are not fully understood by the industry and they are strongly dependent of the tribo-system. However, most of the studies suggest that the lubricity of these coating(s) is\/are determined by interfacial tribo-films generated during sliding (i.e. oxides that are formed during application) and not by the properties of the coatings themselves.\r\n\r\n
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Traditional Binary Nitride Coatings (Mex<\/sub>Ny<\/sub>) were the first PVD commercial PVD coatings to be on the market.<\/p>\r\n\r\n
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