Studies of Ultra Micro Indented Multilayered Sol-Gel Zirconia Films
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2 University of Wollongong, Wollongong, NSW, 2522, Australia CSIRO, Division of Applied Physics, PO Box 218, Lindfield, NSW, 2070, Australia
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ABSTRACT The deformation behavior of sol-gel derived zirconia films during ultra micro indentation has been investigated. The sol-gel films were deposited using a multiple stage coating procedure onto stainless steel substrates. The indentation process was carried out using both pointed indenters, such as a Berkovich, as well as spherical indenters. The use of different indenter types enables the determination of hardness, elastic modulus as well as the elastic-plastic or elasticbrittle transition of the films. The mechanical behavior of thin films is strongly influenced by the interaction between the substrate and the film. In brittle materials, the stress singularities induced by the indentation process cannot readily be reduced by long range plastic flow and may cause cracking. Therefore, a great deal of attention has been paid to post-indentation observations of the films, in particular examinations of the surface morphology for visible traces of the film behavior during indentation. INTRODUCTION Sol-gel deposition of ceramic coatings is a technique that allows thin ceramic films to be deposited onto various substrates of complex shapes. During recent years, a large number of reports on sol-gel deposited ceramic films have been presented as reviewed by Hench and West1 . This technique provides many advantages for industrial applications, mainly because of the low processing temperature, the unique possibility of tailor made combinations to suit different substrate materials and the relative low costs in both equipment and production stages. Sol-gel derived zirconia is used in a number of different applications, ranging from protective coatings used as thermal barriers 2 or in corrosive environments 3 to optical coatings 4 . Several reports have been presented describing different aspects of the sol-gel process, but only minor attention has been paid to the mechanical properties of sol-gel derived films 5-7 . Mechanical properties include hardness, elastic modulus, fracture toughness and strength. With the development of indentation system that use loads and penetration depths in the submicron scale, an excellent opportunity arises to measure mechanical properties by indentation of very thin films 8 -9 . There are several complications involved in distinguishing properties of thin films from composite (film/substrate) properties. Knowledge of film thickness is important as the thickness dictates the changes observed in mechanical behavior, especially when the indentation penetration starts to be influenced by the substrate. The behavior during indentation of thin ceramic films deposited on different substrates has been the subject of a number of investigations 10 -12 .Brittle ceramic films on relatively soft metal substrates have often been found 711 Mat. Res. Soc. Symp. Proc. Vol. 356 ©1995 Materials Research Society
to crack or delaminate during indentation 13- 1 4
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