Development of Spontaneous Infiltration-in situ Production Process for Fabrication of Particulate Reinforced Aluminum Composites

Abstract

The spontaneous infiltration of liquid pure aluminum into the mixture of raw materials is used to synthesize particulate reinforced aluminum composites with the in situ process. The addition of powder of a column IV_a element (Ti, Zr) or a column V_a element (Nb, Ta) into the raw carbide particles of Al₄C₃, SiC or B₄C allows liquid pure aluminum to infiltrate into the mixture spontaneously and subsequently in situ formation of the carbide particles of column IV_a and V_a elements occurs in the melt. It is revealed from macroscopic and SEM observations that liquid aluminum completely infiltrates into the mixture independently of the kind of atmosphere used in the experiment, nitrogen or argon. However, processing under nitrogen gas, which can react with the aluminum melt, is effective in prohibiting pores from remaining in the composite. The rate of in situ reaction of the (Ti+B₄C) system is somewhat high compared to those of (Ti+SiC) and (Ti+Al₄C₃) systems. Very fine TiC and TiB₂ particles simultaneously synthesized through the decomposing reaction of B₄C are dispersed in the aluminum matrix. As soon as liquid aluminum begins to infiltrate, the melt temperature increases drastically not only in (Ti+raw carbide) systems but also in a (Ti+Al₂O₃) system. Hence, it seems that the spontaneous infiltration of liquid aluminum is attributed to the exothermic formation of Al₃Ti.