T.A. Abinandanan

Coarsening of elastically interacting coherent particles—II. Simulations of preferential coarsening and particle migrations

Abstract Three-dimensional multiparticle coarsening simulations have been performed in order to examine the effect of particle misfit on the microstructural evolution of two-phase crystalline systems. The particles are assumed to be coherent, spherical and possess a tetragonal misfit. The system is assumed to be elastically isotropic and homogeneous. The method of multipole tensors in its quadrupole approximation is used to solve the coupled elastic and diffusion problem. The elastic interaction between particles arising from the misfit strains leads to a high degree of particle alignment along elastically favorable orientations. The development of such strong spatial correlations can be understood in terms of such phenomena as enhanced coarsening of unfavorably oriented particles, retarded and inverse coarsening of favorably oriented ones and systematic particle migrations.

Coarsening of elastically interacting coherent particles. I: Theoretical formulation

Abstract The problem of Ostwald repening in binary systems possessing a nonzero volume fraction of elastically and diffusionally interacting particles is examined. Under the assumption that the partial molar volumes of the two components are equal, the elastic and diffusion field equations decouple. This leads to a formulation of the coarsening problem which requires a solution of a multiparticle diffusion problem. The elastic stresses are incorporated into this formulation through the diffusional boundary conditions. The concentration in the matrix phase at the particle-matrix interface is obtained from the assumption of local thermodynamic equilibrium. Assuming particle sphericity, the multiparticle diffusion problem is solved under a quasist approximation using the method of irreducible multipole tensors. Instantaneous radial growth rates and migration rates of the particles are obtained which, in conjunction with a simple time-integration procedure, can be used to simulate coarsening in either stressed or unstressed systems.

Computer simulations of diffusional phase transformations: Monte Carlo algorithm and application to precipitation of ordered phases

A Monte Carlo (MC) simulation technique which is well suited for studying diffusional phase transformations is presented. This technique accounts for atom transport through vacancy migration, and allows a physically meaningful definition of time. This MC technique is used for studying the precipitation of an L1(2) ordered phase from a supersaturated, disordered f.c.c. matrix. Three alloys have been studied of compositions x(B) = 0.125, 0.15 and 0.175, with equilibrium volume fraction of the L1(2) phase of 0.23, 0.47 and 0.71, respectively. The results show that, during early stages of the transformation, both phase separation (i.e. formation of regions of different compositions) and ordering (i.e. creation of atomic order in the solute-rich regions) proceed simultaneously in all the three alloys. In particular, there is no evidence for homogeneous ordering prior to phase separation even in the most concentrated alloy with x(B) = 0.175. Thus, the results are in direct contradiction to those obtained in recent simulations by Chen and Khachaturyan, and underscore the limitations of the Bragg-Williams approximation used by them. The late stage behaviour of all the three alloys obey classical laws of coarsening: (i) the microstructures are self similar, and (ii) the cube of the characteristic microstructural length scale increases linearly with time. Thus, the range of validity of the classical laws appears to extend to large precipitate volume fractions.

Phase field study of grain boundary effects on spinodal decomposition

We have developed a phase field model of a polycrystalline alloy by combining the Cahn–Hilliard model [J Chem Phys 28 (1958) 258] with a model of polycrystals due to Fan and Chen [Acta Mater 45 (1997) 3297]. We have used this model to study grain boundary (GB) effects on spinodal decomposition (SD) in two-dimensional (2D) systems. In binary A–B systems with constant atomic mobility, when the GB-energy

A study of phase separation in ternary alloys

(\gamma\alpha)

Symmetry-breaking transitions in equilibrium shapes of coherent precipitates

of the A-rich

Application of effective potential formalism to mechanical alloying in Ag-Cu and Cu-Fe systems

\alpha

Spinodal decomposition in fine grained materials

phase is lower than that

Development of spatial correlations during coarsening

(\gamma\beta)

Phase inversion in two-phase solid systems driven by an elastic modulus mismatch

of the B-rich