Experimental results in Sn-Cd alloys have been presented that show complex microstructure development in diffusive and convective regimes. Under the diffusive growth conditions, discrete bands or partial bands with different morphologies can form depending upon the growth conditions and the size of the saample. Phase-field calculations have clearly identified the role of competition between the dynamics of growth of the new phase and the parent phase on the development of complex microstructures in the diffusive growth regime. This coimpetition is shown to depend upon the width of the sample. In addition, the simulations have provided an understanding of the different microstructures that can form in a diffusive regime when only a single nucleus of the new phase is allowed to spread from the walls of the container. While this restriction is applicable to narrow samples, it is not realistic for wide samples where multiple nuclei can spread simultaneously. Phase-field simulations thus need to be extended to model the formation of microstructureresulting from multiple nucleation events. Also, complex microstructures that develop at lower G/V ratio where one or both phases become morphologically unstable need to be examined.

        The effects of convection on oscillatory microstructure formation have been examined in detail. It is shown that convection effects can lead to new morphological features. An oscillating convection in the melt is shown to give rise to a novel microstructure in which the primary and the peritectic phases form continuous interconnected microstructure. The microstructure consists of a large tree-like domain of primary a-phase that is embedded inside the peritectic b-phase.

        Theoretical models were discussed that showed that the tree-lke structures formed due to the presence of oscillatory fluid flow. Two different regimes of convection were established: steady convective and unsteady convective regimes. Physical mechanisms that lead to the morphological development under these conditions were also described. In the steady convective regime, the primary a-phase transforms into the peritectic b-phase with a curved a:b interface. In presence of an oscillating convection, the model shows the formation of a tree-like shape of the primary phase, as observed experimentally.

        Experimental results using a new technique in which several samples with different diameters could be directionally solidified simultaneously showed the effect of convection on microstructural development. These studies, for the first time, were able to produce diffusive bands in which repeated nucleation of the two phases occur. In thin samples, under diffusive growth conditions, a rich variety of microstructures, including a coupled growh, were shown to form under dynamical growth conditions.