Functionally graded metal/ceramic composites by tape casting, lamination and infiltration

Alloying aluminum with magnesium and a the use of a N2 atmosphere led to the spontaneous infiltration of ZrO2 preforms with a graded porous structure and the successful fabrication of functionally graded Al–Mg/ZrO2 components. The infiltration process was controlled by an incubation phenomenon resulting from the time needed to destabilize an oxide film present on the molten aluminum droplet. Oxide destabilization depended critically on the presence of Mg, a N2 gas atmosphere and preform microstructure. It is proposed that the destabilization process occurs by a complex reaction localized at the triple point formed between the liquid, solid and gas. The driving force for oxide removal depends on the amount of triple point area present at the infiltration front. A simple model is developed which indicates that this triple point area increases with a decrease in the scale of porosity present in the preform. The model is used to explain the dependence of the incubation time on preform microstructure.