Measurement of Hardness and Young’s Modulus by Nanoindentation

Abstract

Hard nanostructured coatings make high demands on the measurement of their mechanical properties because they are mostly thin (in the thickness range below 5 μm) and very stiff. One of the most popular methods for the determination of their mechanical properties is nanoindentation. Modern instruments reach a depth resolution below 0.1 nm and a load resolution below 1 μN and allow, therefore, very accurate measurements of the penetration of diamond tips into the surface. Indentation modulus as well as indentation hardness can be derived from the load–displacement curve, in addition to some other mechanical properties. The indentation modulus can be slightly different from the Young’s modulus because it is a weighted average of the elastic properties in a certain sample volume and the Young’s modulus is directional. For isotropic materials, however, both values should be equal. In engineering sciences the Young’s modulus is used as a measure of the elastic properties of larger samples, which contain mostly a lot of differently oriented grains. Therefore, it is also a weighted average of single crystalline elastic constants, which are valid in every single grain. This is the reason why both quantities are often not distinguished. In this chapter the term Young’s modulus is used as long as isotropy is taken for granted, and indentation modulus is preferred if the direction dependency plays a role. After a longer discussion in the scientific community, in 2002 the instrumented indentation test of hardness and materials parameters has been standardized in the international standard ISO 14577 part 1–3.1 This standard is not particularly focused on the measurement of film properties. During the successful European project Indentation into Coatings (INDICOAT)2 it became clear that accurate hardness and modulus measurements of coatings require particular care and additional