Nanomechanical characterizations of metals and thin films

The local mechanical properties of different phases and grains in structura l metallic alloys, composites and thin films determine their bulk propertie s and deformation behaviour. A nanoindenting atomic force microscope allows quantitative measurements of the local modulus of elasticity and the nanoh ardness with lateral resolutions of nearly 50 nm, Investigations on differe nt nickel-base superalloys (Waspaloy, CMSX-6), NiAl, gamma-TiAl and steels were performed, where their local mechanical properties could be determined separately on phases with lateral sizes down to 50 nm, With this measureme nt, the hardness of small gamma'-precipitates and of the matrix in the supe ralloys was determined. Other examples are given, where the local mechanica l properties around a crack tip and across a grain boundary were determined . The load-displacement curves obtained for these specimens often show pop- ins similar to yield point phenomena. The estimated maximum shear stress un der the indenter at this load level is comparable to the theoretical shear strength of the materials. The investigations show that the appearance of p op-ins depends strongly on the surface preparation conditions and the exist ence of oxide layers. Investigations of thin gold films on glassy substrates of thickness 20-400 nm show an increasing hardness at lower indentation depths and higher hardn ess values of the thin films in comparison to bulk specimens. Copyright (C) 1999 John Wiley & Sons, Ltd.