TEM Observations of Precipitation of Coherent L12 and D022 Ordered Phases in Ni-V-Ge Alloys
Phase separations of A1 (γ) supersaturated solid solution into γ, cubic-L12 (γ') and tetragonal-D022 (γ") phases were investigated in Ni-V-Ge alloys by means of transmission electron microscopy (TEM). When Ni-15.8at%V-9.0at%Ge alloy is aged at 1073 K, at the early stage of ageing γ" phases are observed in the γ matrix as triangle- or diamond-shaped precipitates. With further ageing, colonies of lamellar structure consisting of two variants of γ" phase are dispersedly formed in the γ matrix and then γ" plates grow along the <110> direction. When Ni-14.5at%V-8.8.at%Ge alloy is isothermally annealed at 1023 K, first spherical γ' particles precipitate homogeneously in the γ matrix, followed by the formation of lamellar structure of γ" phases. In the course of further ageing, the lamellar structure develops, and only γ' particles around the lamellar structure grow and others gradually fade out.
Young Won Chang, Nack J. Kim and Chong Soo Lee
Y. Inuzuka et al., "TEM Observations of Precipitation of Coherent L12 and D022 Ordered Phases in Ni-V-Ge Alloys", Materials Science Forum, Vols. 561-565, pp. 2365-2368, 2007