A new method for fast statistical measurement of interfacial misfit strain around nano-scale semi-coherent particles

Abstract

An innovative diffraction contrast imaging method derived from Ashby–Brown contrast is presented for fast and statistical measurement of interfacial misfit strain around nano-sized semi-coherent particles. A correlation between nano-scale interfacial misfit strain and the fringe-like transmission electron microscopy (TEM) contrast lines was set up, by which interfacial misfit strain could be obtained by measuring the inter-spacings between the so-called “no-contrast” lines. The mechanism of the measurement lies on the symmetry of the strain field at specific orientations around semi-coherent particles due to the presence of misfit dislocations, which induces “no-contrast” lines on TEM images under proper two-beam conditions. A much lower average lattice misfit strain of 4%, rather than 9.45% expected from lattice misfit between matrix and precipitate crystals, was revealed along (02)_Matrix in austenitic oxide dispersion strengthened steel by this method, and was confirmed by geometric phase analysis (GPA) on high resolution transmission electron microscopy (HRTEM) images. This diffraction contrast imaging method is especially suitable for measuring misfit strain around particles that are smaller than 10 nm, and is expected to bridge the gap between nano-scale interfacial structure and mechanical properties of materials that are strengthened by semi-coherent nano-particles.