Microstructure morphology and solute segregation in non-equilibrium solidification of metastable immiscible Cu50Co50 alloy

AbstractNon-equilibrium solidification of undercooled metastable immiscible Cu50Co50 alloy was performed by using glass-fluxing coupled with cyclic superheating method. The evolutions of microstructure morphology and solute segregation were elucidated as a function of initial undercooling. As for the samples undercooled by 62K and 105K, α-Co dendrites form primarily from the homogeneous liquid phase and then break into granular grains during the recalescence process. Moreover, the growth of dendrite changes from the solute-controlled mode to thermal-controlled mode with increasing undercooling, which generates the reduction of trunk size and the increase of solute content. In contrast, dual-layer structure prevails for larger undercoolings, i.e., 188K and 220K, where the strengthened immiscible effect leads to the decrease of solute content in separated phases and the occurrence of second separation. As for the sample with separated melt structure, nucleation triggering was adopted and serious shrinkage cavities can be observed due to the inadequate feeding of residual liquid

The transition of alpha-

High undercooling up to 550\un{K} (0.39 T_{\ab{E}}) was achieved in eutectic \chem{Ni_{78.6}Si_{21.4}} melt using glass fluxing combined with the cyclic superheating. According to the microstructure evolution with the initial undercooling, surprisingly, a transition from non-faceted to faceted phase occurs for the as-solidified morphology of the alpha-\chem{Ni} phase at the undercooling of 390\un{K}. On the basis of the entropy of fusion criterion and the interface kinetics, this interesting morphology transition at high undercooling is analyzed