Intermetallic compound layer growth at the interface of solid refractory metals molybdenum and niobium with molten aluminum

The growth mechanisms and growth kinetics of intermetallic phases formed between the solid refractory metals Mo and Nb and molten aluminum have been studied for contact times ranging from 1 to 180 minutes at various temperatures in the range from 700 to 1100 degrees C. The growth of the layers of the resulting intermetallic phases has been investigated under static conditions in a saturated melt and under dynamic condition using forced convection in unsaturated aluminum melts. The Nb/All interfacial microstructure consisted of a single intermetallic phase layer, Al3Nb, where as two to four different phase layers were observed in the Mo/Al interface region, depending upon the operating temperature. It was found that, in a saturated melt, the intermetallic phase growth process was diffusion-controlled. The parabolic growth constants of the first and second kind and integral values of the chemical diffusion coefficients over the widths of the phases were calculated for both Mo/Al and Nb/Al systems. It also was found that the AlNb2 phase grew between the Nb and Al3Nb phases after consumption of the saturated Al phase. Similarly, the AlMo3 phase grew between the Mo and Al8Mo3 phases with the diminishing of all the other existing compound phases. In an unsaturated melt, the intermetallic phase layer grows at the solid surface while, simultaneously, dissolution occurs at the solid/liquid interface. This behavior is compared to the growth mechanisms proposed in existing theories, taking into consideration that interaction occurs between neighboring phases