Microstructure characterization of ceramic composites formed by controlled melt oxidation of Al-Mg-Pd alloys

Ceramic matrix composites were produced by controlled melt oxidation of Al_98-xMg₂Pd_x alloys. The Pd element was chosen as an additive due to its influence on the thermodynamic conditions at the oxidation front and its effect on the surface tension of liquid aluminum. The Al_98-xMg₂Pd_x alloys were prepared from uniaxially cold pressed metal powders mixtures, heat-treated in an Argon atmosphere prior to the controlled oxidation process, which was conducted at a temperature of 1200°C, for 6 hours. The growth rate was evaluated according to weight gain measurements, the microstructure of the grown composites was investigated by optical microscopy and scanning electron microscopy (SEM). Micro-chemical analysis was performed using an electron microprobe analyzer (EPMA). Phase characterization was carried out using X-ray diffractometry. It was found that Pd addition increases the growth rate, the metal volume fraction and the diameter of the metal channels. Pd also promotes the formation of a uniform microstructure. The results strongly support the assumption that the wetting conditions between the melt and the Alumina grains and the thermodynamic conditions at the oxidation front have an important role in the controlled melt oxidation process.