Consumption of SiC whiskers by the Al–SiC reaction in aluminium-matrix SiC whisker composites

Abstract

The Al–SiC reaction in aluminium-matrix SiC composites made by liquid metal infiltration resulted in the formation of silicon, the amount of which increased with increasing SiC volume fraction, but the fraction of SiC consumed by the reaction increased with decreasing SiC volume fraction. For SiC whisker composites made at an infiltration temperature of 800 °C, the fraction of SiC consumed was 18, 26 and 55% at SiC volume fractions of 0.31,0.23 and 0.10, respectively. The fraction of SiC whiskers consumed was inversely proportional to the volume fraction of SiC whiskers in the composite. The product of these two fractions provides a scale (called the reactivity index) that describes the Al–SiC reactivity. The index decreased with decreasing infiltration temperature and was higher for SiC whiskers than SiC particles. Even at an infiltration temperature of 670 °C, the fraction of SiC whiskers consumed was 26% at an SiC volume fraction of 0.10. In contrast, the fraction of SiC consumed was only 8.4% for a 55 vol.% SiC particle composite made at an infiltration temperature of 800 °C. The fractional consumption values were obtained by determining the silicon concentration in the aluminium matrix via calorimetric measurement of the liquidus-eutectic temperature difference.