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

Abstract

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.

Keywords:

• phase transformation kinetics
• microstructure
• precipitation
• modelling

Acknowledgements

The authors thank Dr. P. Caron (ONERA, France) for Ni–V single crystal growth. The simulations were carried out in the CRIHAN centre under project 1999006.