Study of the compaction behavior of composite powders under monotonic and cyclic loading

The consolidation behavior of composite powders during pressure cycling at room temperature in uniaxial compaction experiments was studied and compared with monotonic compaction. Aluminum and various amounts of SiC powders (up to 50 vol%) were used to investigate the effect of hard reinforcement particle on the densification of soft aluminum matrix. The cyclic compaction was carried out at various pressure amplitudes, ranges from 90 to 360 MPa, at the frequency of 1 Hz. The pressure cycling was continued up to 5000 cycle, in which, the rate of consolidation was found to be fairly low. The consolidation of the composite powders under different loading modes was analyzed through density–pressure diagram and related to the Heckel compaction equation that is one of the most common ones today. The effects of loading mode, i.e., monotonic and cyclic, and the amounts of reinforcement on the densification of Al–SiC composite powders were related to the yield pressure, 3σ0 (σ0 is the yield strength of powder material). It was found that pressure cycling enhances the densification of composite powders. This observation is related to the deviatoric stresses generated by volumetric mismatch due to the different compressibilities of the phases that decreases the yield pressure of the composite powders under cyclic loading. The mismatch yield pressure induced by pressure cycling increases as the amount of reinforcement particles is increased. This results in an enhancement in the densification rate for the composite compacts composed of high volume of the ceramic particles during pressure cycling. This article addresses the effects of compaction mode and reinforcement particles on the densification, microstructure and mechanical properties of Al–SiC composite powders.