EXPLORING SIZE EFFECTS IN COPPER-CHROMIUM-ZIRCONIUM USING INDENTATION TECHNIQUES AND IN-SITU MICRO-PILLAR COMPRESSION

摘要

The influence of microstructure on the mechanical properties of materials has been the focus of research over several decades, with various attempts made to characterize this size effect numerically, e.g. the Hall-Petch relationship. This behaviour is overlaid with an extrinsic size dependence that scales with the testing technique used, whereby the smaller the sampled volume the stronger the material appears to behave. Considering the growing trend towards miniaturised mechanical testing, particularly in the electronics industry and nuclear community, both forms of the size effect need to be fully understood in order to achieve engineering-relevant results. In particular, knowing how the two contribute cumulatively in different material systems is non-trivial and requires further investigation. In this work several materials with different strengthening mechanisms are tested at a range of length-scales in order to explore the combined effect on elastic and plastic deformation. A variation in the dominant microstructural length-scale was achieved via solid solution strengthening, precipitation hardening, grain size reduction and the addition of proton-induced irradiation defects in CuCrZr, which was chosen due to its role in heat sink components of current and future experimental fusion reactors. The small-scale test techniques used were Berkovich indentation, spherical indentation and in-situ pillar compression, which spanned test lengths from 10's nm to 100's μm. It was found that there is no one mechanism that can be used to describe the material response at all stages of deformation, therefore any scaling model hoping to predict bulk-scale response from small-scale testing must take into account multiple factors, including dislocation source availability, size and motion. The sensitivity to microstructure was also found to vary with different test methods, for example in pillar compression experiments (Fig. 1) where after irradiation there was no apparent extrinsic size effect due to the dominating irradiation defects.