Phase field theory of polycrystalline freezing in three dimensions

Tamás Pusztai1, G Bortel, László Gránásy1,2

1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, Budapest H-1525, Hungary
2BCAST, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom

A phase field theory, we proposed recently to describe nucleation and growth in three dimensions (3D), has been used to study the formation of polycrystalline patterns in the alloy systems Al-Ti and Cu-Ni. In our model, the free energy of grain boundaries is assumed proportional to the angular difference between the adjacent crystals expressed in terms of the differences of the four symmetric Euler parameters called quaternions. The equations of motion for these fields have been obtained from variational principles. In the simulations cubic crystal symmetries are considered. We investigate the evolution of polydendritic morphology, present simulated analogies of the metallographic images, and explore the possibility of modeling solidification in thin layers. Transformation kinetics in the bulk and in thin films is discussed in terms of the Johnson-Mehl-Avrami-Kolmogorov approach.