Indentation response of a superlattice thin film revealed by in-situ scanning X-ray nanodiffraction. (15th August 2020)

• Record Type: Journal Article
• Authors: Todt, J.; Krywka, C.; Zhang, Z.L.; Mayrhofer, P.H.; Keckes, J.; Bartosik, M.
• Is Part Of: Acta materialia. Volume 195(2020)
• Page Start: 425
• Page End: 432
• Publication Date: 2020-08-15
• Subjects: Nanoindentation -- Superlattice -- Thin film -- Synchrotron diffraction -- In situ; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2020.05.056
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Nanocrystalline materials such as thin films, and in particular, multilayers with a periodicity in the nanometer range, i.e. superlattice films, possess properties that cannot be found in their coarse-grained bulk counterparts. Mechanical characterization of such structures is therefore of high interest, but also very challenging, due to the small length scales involved and has therefore most often been performed ex-situ using electron microscopy. In this work, however, we report on the first in-situ micromechanical analysis of a CrN-AlN superlattice thin film cross-section. The sample was deposited using reactive magnetron sputtering and sublayer thicknesses were chosen so as to stabilize AlN in its cubic crystal structure. Using a synchrotron X-ray nanoprobe, maps of internal stresses and morphological changes were tracked by means of wide-angle X-ray diffraction and simultaneous small-angle X-ray scattering, while the sample was loaded to various degrees with a wedged diamond tip. The results reveal a high compressive strength of about 13 GPa, while through-thickness cracks form, following tensile stresses >1.4 GPa and thereby provide a relaxation mechanism. Layer rotation up to several degrees and significant layer compression up to 7% were also found, but along with the internal stress response, their nature is mostly elastic, meaning that in the post-loading state only a fraction of the effects observed under load remains. Graphical abstract: Image, graphical abstract