Short range order in Ni4Mo and its high resolution electron microscope images

The short range ordered (SRO) structure in Ni4Mo has been investigated by means of high resolution transmission electron microscopy with digital image processing and Monte Carlo simulation. High resolution transmission electron microscope (HRTEM) images were recorded with an Imaging Flare (IP) system. Conventionally printed images of the SRO state exhibit locally dot patterns corresponding to N2M2-type (chalcopyrite-like) structure. However, the dot patterns transform into those of subunit cell clusters of D1(a), D0(22) and Pt2Mo structures, when the image is output with a different gray scale. The Monte Carlo simulation with appropriate interaction parameters of atoms has explained successfully the HRTEM images. It is concluded that the SRO state in Ni4Mo involves subunit cell clusters of D1(a), D0(22) and Pt2Mo structures in the atomistic level of microstructure. The concept of [1 1/2 0]* static concentration waves corresponding to the N2M2 pattern is rationalized as a mesoscopically averaging view of the SRO state. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.