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

Ceramic matrix composites were produced by controlled melt oxidation of Al9 8-xMg2Pdx alloys. The Pd element was chosen as an additive due to its influ ence on the thermodynamic conditions at the oxidation front and its effect on the surface tension of liquid aluminum. The Al98-xMg2Pdx alloys were pre pared from uniaxially cold pressed metal powders mixtures, heat-treated in an Argon atmosphere prior to the controlled oxidation process, which was co nducted at a temperature of 1200 degreesC, 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 elect ron microscopy (SEM). Micro-chemical analysis was performed using an electr on microprobe analyzer (EPMA). Phase characterization was carried out using X-ray diffractometry. It was found that Pd addition increases the growth r ate, the metal volume fraction and the diameter of the metal channels. Pd a lso promotes the formation of a uniform microstructure. The results strongl y support the assumption that the wetting conditions between the melt and t he Alumina grains and the thermodynamic conditions at the oxidation front h ave an important role in the controlled melt oxidation process. (C) 2001 Kl uwer Academic Publishers.