Theoretical analysis of strain-induced shape changes in cubic precipitates during coarsening

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · Acta Metall.; (United States)

DOI:https://doi.org/10.1016/0001-6160(88)90224-6· OSTI ID:6760070

Khachaturyan, A G; Semenovskaya, S V; Morris, Jr, J W ^[1]

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1. Dept. of Materials Science and Mineral Engineering, Univ. of California, Berkeley and Center for Advanced Materials, Lawrence Berkeley Lab., Berkeley, CA (US)

The work reported here concerns the evolution of the shape of a coherent, cubic precipitate as it grows by coarsening. The work was motivated by the need to explain recent experimental observations that show that cuboidal ..gamma.. Ni/sub 3/Al precipitates in Ni-Al alloys resist coarsening and decompose into doublets of parallel rectangular plates and octets of small cubes. The theoretical model assumes a precipitate of cubic phase with negative elastic anisotropy, and neglects any difference between the elastic constants of the precipitate and the matrix. The elastic energy of the precipitate is then calculated as a function of its morphology, including the possibility of decomposition into doublets or octets of discrete particles. The results show that a cuboidal precipitate with (100) faces and edge length, 2a, is metastable with respect to transition to a doublet of discrete plates, with dimensions a x 2a x 2a, that are separated by the distance ..mu.. - a, when the edge length exceeds a characteristic distance, that depends on the interfacial tension of the precipitate, its elastic constants, and its misfits with the parent lattice. When the edge length of the doublet exceeds a critical value, it becomes metastable with respect to transformation into an octet of cubic particles that have edge length /100/ interfaces and an interparticle separation of 0.4a. The octet of particles becomes metastable with respect to coagulation into a thin plate on the (100) plane on further coarsening. If the interfacial tension is isotropic, the same analysis can be used to predict the transition from sphere to cube. The equilibrium transformation sizes are specifically computed for the case of ..gamma.. Ni/sub 3/Al, and are consistent with the experimental data. The possible influence of the strain energy is on coarsening is also discussed.

• OSTI ID: 6760070
• Journal Information: Acta Metall.; (United States), Journal Name: Acta Metall.; (United States) Vol. 36:6; ISSN AMETA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
ANISOTROPY
DATA
ELASTICITY
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
HARDENING
INFORMATION
LATTICE PARAMETERS
MATHEMATICAL MODELS
MATRICES
MECHANICAL PROPERTIES
METASTABLE STATES
NICKEL ALLOYS
NUMERICAL DATA
OCTET MODEL
PARTICLE MODELS
PARTICLES
PHASE STUDIES
PRECIPITATION
PRECIPITATION HARDENING
SEPARATION PROCESSES
SHAPE
STRAINS
TENSILE PROPERTIES
THEORETICAL DATA