EVALUATION OF THE MECHANICAL PROPERTIES OF CERAMICS AND THIN HARD CERAMIC COATINGS USING NANOINDENTATION

Abstract

Nanoindentation testing is one of the only techniques that allows material responses to contact stresses to be explored in a controlled way and at high spatial resolutions of both contact depths and lateral position. Consequently, nanoindentation techniques are invaluable both for studying the mechanical properties of solids—especially brittle materials—in a nondestructive manner and for assessing the mechanical properties of surfaces at the spatial scales commensurate with tribological response.

While microhardness indentation testing has found widespread use in studying many aspects of the plastic deformation and fracture of solids, the usual reliance on post-facto measurements of indentation size has been a significant limitation. For example, it has been difficult either to assess the amount of recoverable elastic deformation contributing to the indentation process or to make detailed studies of deformation transitions (e.g the elastic-toplastic transition).

The advent of continuously recording indentation tests (CRIT), such as nanoindentation, is now allowing significant advances to be made in applying contact mechanics through controlled indentation tests—especiaLly in the areas of both decreasing the spatial scales of tests and obtaining a complete load—displacement—time—contact stiffness history of each test. While the load—displacement curve from a CRIT test contains all the basic information involved to fully understand the mechanical response of a material to each test (it can be regarded as a mechanical "fingerprint"), it is often necessary to further process this data and test such responses against a number of models for a full understanding of the system properties. Using examples from the areas of ceramics and ceramic coatings, this paper reviews some of the advances, which have been made in applying CRIT techniques to the characterization of the mechanical properties of materials. For example, the elastic-plastic transition in materials such as Al₂O₃ and SiC is now well understood and it is possible not only