Nanoindentation Hardness of Compositionally Modulated Ti/TiN Multilayered Films
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deformation hardness obtained. INTRODUCTION Multilayer coatings of either single crystal or polycrystalline materials, with a large number of repeated layers, have been intensively studied in the last decade to enhance mainly tribological performance of the coatings. The enhancement of the coating performance is achieved by combining the layers with different mechanical properties. It is first reported that TiN/VN multilayer coatings epitaxially grown on MgO single crystals provide a hardness of 5600kgf/mm2 that was much higher than the hardness of TiN or VN single crystal coatings'). The similar results were also reported for TiN/NbN2 ). The superlattice period that provided a maximum hardness value was in the range of 5-6nm. For polycrystalline TiN/VN multilayer coatings, it was shown that the highest hardness of 5200kgf/mm2 was obtained for a film with a superlattice period of 6nm among the films with superlattice periods ranging from 2.5nm to 150nm3'. In recent study for polycrystalline AI/A120 3 and Ti/TiN multilayer, the change in the hardness measured by a nanoindentation method was found to depend on metallic layer thickness and described by a Hall-Petch type equation4O. More studies have been performed for multilayer coatings of TiN/W2 N5 )and Ti/TiN 6"7)coatings. In 577 Mat. Res. Soc. Symp. Proc. Vol. 505 0 1998 Materials Research Society
these studies, no clear dependence of hardness on a compositional modulation period has been shown. The mechanisms of deformation, cracking, and delamination have been also studied for Ti/TiN multilayer coatings'). Although the mechanisms of enhancement of mechanical and tribological properties by using the multilayer structure have not been well understood, a large number of the interfaces or laminated structures are crucial to improve tribological properties. Since the interface seems to play an important role in the enhancement of the properties, it is expected that the films with stronger lamination with a large number of repeated layers provide better tribological properties. A compositionally modulated multilayer films without any interrupted interfaces is one of this type of films. In this study, dependence of hardness on modulation period was investigated for compositionally modulated Ti!TiN multilayer coatings. In addition, by using a nonoindenttation
method to measure hardness, both plastic and elastic propeties of sample coatings can be estimated. This will give us more information about the mechanisms of the hardness enhancement. EXPEIMENT
Film Preparation Multilayer films of Ti/TiN multilayer films were deposited by a reactive gas flow rate modulation magnetron sputtering method using a combination of a Ti metal target and an Ar-N2 mixture discharge gas. In this method, a N2 gas flow rate was automatically controlled by a computer-controlled mass flow controller to produce films with an optimized composition distribution. The sputtering apparatus used in this experiment was a batch-type sputtering machine L100S-FH of ANELVA corporation. The process chamb
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