CHARACTERIZATION OF SEVERITY OF PARTICLE CLUSTERING AND ITS EFFECT ONFRACTURE OF PARTICULATE MMCS

The issues involved in characterising the spatial distribution of rein forcement 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 ale presented iom microstructural analy sis and mechanical resting of a number of Al-Si/20 vol.-%SiCp MMCs pro duced by different processing routes. The most useful parameter for ch aracter ising the severity of clustering is found to be the ratio of t he variance of the distribution of the cell areas to the corresponding variance obtained from a random particle distribution with the same a verage areal density of particles. Either Dirichlet oi particle growth tessellation procedures can be used. High values of the clustering pa rameter were found to correlate with low ductilities. The transition f rom random to significantly regularised microstructures correlates wit h a sharp increase in ductility for materials with similar (low) poros ity contents and microstructural constitution. The parameter, which ca n be evaluated using standard image analysis techniques, is therefore proposed for wider use in clustering studies and quality control proce dures for particulate MMCs. MST/4030.