Mechanical, Tribological & Topographic Characterisation of Systems Surface-Engineered with Thin, Hard, CNx Coatings

CNx coatings with high hardness and stiffness are attracting considerable interest at present since there is some theoretical work which indcates the Carbon nitride with the beta-silicon nitride structure could have superior mechanical properties to diamond. CNx films are not generally fully crystalline but have been shown to have a fullerene-like stucture and may consist of arrays of nanotubes. It is this structure which leads to their very interesting mechanical properties. High hardness and elastic modulus have been measured for CNx films but there are considerable problems with obtaining reliable measurements because traditional methods of data analysis are not applicable. This project is aimed at improving our understanding of the mechanical properties of CNx coatings by developing improved test procedures and better analytical strategies for understanding test data.

Nanoindentation testing of fullerene-like CNx on Silicon

The project involves using state-of-the-art nanoindentation, scanning probe microscopy (SPM), scanning electron microscopy (SEM), optical profilometry, instrumented scratch tests, wear tests and modelling routines to assess the mechanical,tribological and topographic characteristics of a range of CNx coatings produced in other laboratories. The aim is to develop an understanding of the role of these parameters in determining overall system performance. This will not only require the measured properties to be correlated with process path (and thus microstructure) such that system properties may be controlled and optimised for particular applications, but also that system performance is understood in terms of soundly-based property modelling. Suitable strategies and numerical procedures have already been established at Newcastle, including, for example, how high spatial resolution nanoindentation procedures can be used to establish both the hardness and elastic modulus of the 'coating only' and how the overall coated system performs macroscopically, as substrate deformation and yield becomes important, but need to be developed further for CNx coatings. Further, the role of interfacial adhesion, residual stresses and environment in determining performance is also being explored and quantified. Parallel studies utilise hot-hardness tests, fully-instrumented scratch and wear tests and specially-developed bend tests to enable the fundamental properties determined by nanoindentation etc to be linked to macroscopic tribological behaviour. Such tests also allow the critical influences of temperature, surface topography and humidity to be quantified. Modelling in terms of predicting both the performance of coated systems (from a fundamental deformation-mode basis) and the micromechanics governing nanoindentation response is an important part of the project.

The project is funded by an EC TMR grant and an EC IHP grant and involves travel to laboratories of the collaborating partners in Sweden, France and Germany.

This page was last modified on 18th January 2002.

S.J.Bull@ncl.ac.uk

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