Cellular Model Simulations of Solidification Structures in Ternary Alloys.

摘要

Solidification processes are an important part of many modem manufacturing processes. They can be found in different casting and welding processes. The solidification structure is very important for the quality of any product manufactured by such processes. This is so because the casting or weldment microstructure determines their mechanical properties. For welding processes, solidification theories can explain the evolution of the fusion zone microstructure and how this microstructure is influenced by the solidification parameters such as the temperature gradient and the solidification rate. In order to investigate the solidification parameters' effect on the microstructure, a numerical model based on Cellular Automaton combined with the finite difference method (CA-FD) is presented in this thesis. The simulation is conducted on a finite three dimensional control volume of the fusion zone. The model takes into account the solute-, curvature-, and kinetic undercooling. The temperatures are assumed to be distributed linearly within the control volume. The model predicts the morphology and density of the microstructure according to different values of the cooling rate and initial temperatures. It is demonstrated that the solidification structure has a columnar morphology at high temperature gradients and low cooling rates. The morphology changes to dendritic as the temperature gradient decreases and/or the cooling rate increases. It is also shown that an increase in the cooling rate results in the densification of the solidification structure. The results demonstrate that an increase in the initial substrate roughness can result in the increase in the density of the solidification structure. The simulation results show an agreement with the constitutional undercooling theory of solidification structures.