Short range order structures in fcc-based Ni–Mo studied by high resolution transmission electron microscopy with image processing

Modern high resolution transmission electron microscopy was employed in study of short range order (SRO) in fcc-based Ni–Mo, which is classified as ‘1 1/2 0 alloy’. Digital processing of high resolution transmission electron microscope (HRTEM) images can give information about local atomic arrangements of SRO as well as their projection views. The HRTEM observation with image processing reveals the SRO structures in Ni–Mo depending upon the alloy composition and the heat treatment. Subunit cell clusters of D1a, D022 and Pt2Mo structures are generated in the SRO states of Ni4Mo and Ni3Mo alloys. In the initial SRO states, the number of Pt2Mo type clusters increases with Mo composition while that of D1a type decreases. The D1a, D022 and Pt2Mo type clusters increase in number in the early stages of subsequent ordering. The formation of D1a, D022 and Pt2Mo type clusters in the SRO states is rationalized in terms of the similar tendencies in atomic configuration between D1a, D022 and Pt2Mo structures.