Kinetics of cubic-to-tetragonal transformation in Ni-V-X alloys

Computer simulations based on the Khachaturyan's Onsager diffusion equation have been performed to model microstructure evolution during the cubic-to-tetragonal transformation in Ni-based alloys. A 2D model was employed. The fcc-DO22 ordering has been studied as a model case of this type of transformation. Particular emphasis is placed on the formation mechanism of DO22 monovariant structures. Computer simulations demonstrate that strain-induced interactions between coherent DO22 precipitates lead to the formation of intermediate two-variant chessboard-like structures, which are found to be unstable and coalesce into subsequent single-variant maze structures. It is shown that the stability of the chessboard-like structures is very sensitive to lattice misfits. These simulation results are in good agreement with TEM observations.