Ordering process of Cu3Pt from short-range order state studied by in-situ TEM observation

The state of short-range order (SRO) and the ordering process in Cu3Pt have been studied by the in-situ transmission electron microscope observation m ethod. In order to detect weak diffraction-patterns and weak image-contrast s, an imaging plate system and/or digital-process of video-recorded signals were applied. It is confirmed that above the critical temperature for orde ring, T-c, the alloy shows diffuse scattering in its electron diffraction p attern. The appearance of the diffuse scattering indicates that the "disord ered" Cu3Pt (designated as A1) has an SRO-state in thermoequilibrium. Dark field images taken by using the diffuse scattering shows a fine dot-contras t, which indicates the presence of "microdomains". The dot-contrast is flic kering at higher temperatures, but the rate of flickering decreases with fa lling temperature and finally stops before reaching T-c. On further decreas ing temperature, some of the microdomains grow up to large domains of the l ong period superstructure (L1(2-s),) phase. This indicates that the transfo rmation to L1(2-s) via SRO proceeds without a process of nucleation even th ough the transformation is of a first-order. (C) 2000 Elsevier Science Ltd. All rights reserved.