The effects of elastic interaction energy on the γ′ precipitate morphology of continuously cooled nickel-base alloys

Abstract The morphological change of γ′ precipitates in some nickel-base alloys continuously cooled across the γ′ solvus line was investigated by means of transmission electron microscopy. In slowly cooled (e.g. a cooling rate of about 10−2 K s−1) NiAl , NiSi and Nimonic 115 alloys a single γ′ particle split into eight small cuboids (i.e. an ogdoad) and the unit assemblies of particles, each of which consisted of eight cuboids, were closely distributed in the γ matrix. For quickly cooled (e.g. a cooling rate of about 10 K s−1) alloys, splitting did not occur and a large number of small γ′ particles were closely aligned along 〈100〉 directions. In NiAl alloys, γ′ precipitate ogdoads were formed during slow continuos cooling, whereas γ′ precipitate doublets were formed during the isothermal aging just below the γ′ solvus line. Such morphologies were introduced by the strong influence of the elastic interaction energies.