Reactive synthesis of in-situ ZrAl3-Al2O3-Al composites

Abstract

In this work, a reactive synthesis process is proposed to obtain ZrAl3-Al2O3 particulate-reinforced aluminum matrix composites. The process involves the in-situ formation of Al2O3 and ZrAl3 from Al-ZrO2 green compacts. Upon compact heating, it is found that reduction of ZrO2 by molten aluminum occurs at temperatures above 750 °C, leading to the development of ZrAl3 and Al2O3 phases. Thermodynamically, it is found that the reduction of zirconium oxide is driven mainly by the dissolution of Zr in molten aluminum. Because the solubility of Zr in liquid aluminum is extremely small, the formation of ZrAl3 is favored after relatively small Zr dissolutions. The first Zr-Al intermetallics to form at the lowest temperatures seem to be metastable, as infered from the measured atom ratios for Al : Zr of 2.83 : 1. At increasing temperatures, the reaction comes into completion, resulting in the formation of equilibrium intermetallic ZrAl3 phases. The results obtained from differential scanning calorimetry (DSC) indicate that by increasing the scanning rates, both the reaction temperature and the exothermic peak intensity also increase. Alternatively, it is found that by reducing the amount of ZrO2 in the green compact, the in-situ reaction temperatures also shift toward higher values.