Characterisation of severity of particle clustering and its effect on fracture of particulate MMCs

Abstract

The issues involved in characterising the spatial distribution of reinforcement particles in MMCs are briefly explored. It is concluded that tessellation of the microstructure into cells, each of which contains a single particle, is necessary if comprehensive characterisation is required. Experimental results are presented from microstructural analysis and mechanical testing of a number of AI-Si/20 vol.-%SiC_p MMCs produced by different processing routes. The most useful parameter for characterising the severity of clustering is found to be the ratio of the variance of the distribution of the cell areas to the corresponding variance obtainedfrom a random particle distribution with the same average areal density of particles. Either Dirichlet or particle growth tessellation procedures can be used. High values of the clustering parameter were found to correlate with low ductilities. The transition from random to significantly regularised microstructures correlates with a sharp increase in ductility for materials with similar (low) porosity contents and microstructural constitution. The parameter, which can be evaluated using standard image analysis techniques, is therefore proposed for wider use in clustering studies and quality control procedures for particulate MMCs.