Nanoindentation in Irradiated Materials

In this chapter, the authors discuss the theory and practice of nanoindentation techniques, with a particular focus on their application in assessing the mechanical properties of irradiated materials. In particular, nanoindentation is extremely useful in studying the mechanical properties of the thin layer of damaged material in ion irradiated samples. Since the radiation process involves phenomena at multiple time scales (ps to decades) and length scales (nm to m), this chapter focuses on the time and length scales most readily probed by nanoindentation – around the hours to years scale in time and microns to millimetres in length. First, some basic theory of nanoindentation and the associated instruments and their corresponding advantages and drawbacks are discussed. The chapter proceeds to describe two of the major techniques to probe ion irradiated materials – “top-down (TD)” and “oblique cross section (OCS)” nanoindentation, using continuous stiffness mode (CSM) and non-CSM mode respectively. Simultaneously, the methods used for correcting for the “indentation size effect (ISE)” are also discussed. It goes on to the application of finite element (FE) and crystal plasticity finite element (CPFE) methods to the modelling of deformation and stress fields around indenters in unirradiated and ion irradiated materials, using available data for irradiation induced hardening. These models used discrete elements to divide the irradiated layer into multiple thin layers with respective individual doses, and were shown to be successful in reproducing experimental nanoindentation results in metallic alloys such as SS316 and AA6061. Thus the authors demonstrate here the usefulness of a combination of nanoindentation and continuum modelling in understanding the mechanical properties of irradiated materials.