In situ TEM observation of long range ordering via short range order in Cu3Pt

The thermoequilibrium state of short range order (SRO) and the ordering pro cess to the long range order (LRO) phase in Cu3Pt have been studied by the in situ transmission electron microscope (TEM) observation method. It is co nfirmed that the alloy has the SRO state in thermoequilibrium within the te mperature region for the disordered fee phase (designated as A1). The SRO s tate can be interpreted in the 'microdomain model'. The degree of order flu ctuates temporally as well as spatially at higher temperature, but freezes at a lower temperature in the A1 region. In the temperature region of (A1 LRO), some of the microdomains in the SRO grow np to large domains of LRO. This indicates that the transformation process to LRO via SRO proceeds wit hout a process of nucleation even though the transformation is of a first o rder. Division of A1 into subregions and physical meaning of the phase boun dary between (A1 + LRO) and A1 are discussed.