A study of the structure of codeposited PVD coatings
The structure of two-component coatings codeposited by magnetron sputterion plating was studied. This apparently simple topic has never been studiedsystematically and has led to a number of unexpected and very interestingresults.The systems that were studied included materials with 100% solid-solubility,(titanium and zirconium) totally insoluble materials (chromium and copper)and materials that can form intermetallic compounds (titanium andaluminium). Variables studied included method of deposition, composition ofthe coating and energy of ion bombardment during deposition. Twoapproaches were used for the deposition process. These were multilayerdeposition from vertically opposed magnetrons and codeposition from coplanarmagnetrons, both using closed field magnetic arrays. Both methods arefundamentally the same. It is the orientation and manipulation of the substratesduring the deposition process which leads to either a multilayer coatingstructure or a codeposited homogeneous coating. The flexibility of the coatingtechnique was demonstrated and a greater understanding was gained of boththe structure and properties of alloy coatings and how these are influenced bythe deposition parameters in a magnetron sputtering system. The coatingstructures were studied using SEM and XRD and their properties by differentmechanical tests. Prior studies in this field have shown that such coatings canhave unexpected properties. For example, energetic ion bombardment isknown to cause the production of 'non equilibrium' phases and can extend thenormal solubility range. Thus HCP Ti-Al coatings can be deposited whichwould be expected to have good tribological properties. Properties such asthis have been studied and exploited for suitable applications. Further studiesshowed how parameters such as ion current density are dependant on targetcurrent and have a large influence on coating structures and properties. This isall of importance to materials scientists, surface engineers and manufacturersof coating equipment.
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