Acoustic studies of the effect of SiC particle reinforcement on the compaction of alumina powder

Abstract

A number of acoustic techniques namely, ultrasonic (US), acousto-ultrasonic (AU) and acoustic emission (AE), were employed to study the effect of reinforcement in the form of SiC particles on the compaction of spray-dried alumina powder. The US and AU techniques were shown to be capable of monitoring the processes occurring during loading and unloading, whereas AE could be used, in certain cases, to monitor the relative movement of particles in a powder compact during stress relaxation. The results were consistent with three stages of compaction, namely rearrangement of agglomerates, agglomerate breakdown and elastic deformation. The two pressure break-points between the stages i.e. P 1 and P 2 the pressures corresponding to the onset of breakdown of the agglomerates and to the change from permanent to elastic deformation, respectively, were determined by a number of different methods as a function of SiC content (10–40 vol%), type (equiaxed, angular or platelet) and size.