Problems With Correlation Between The Structure And Properties Of Metal Cast Composites Reinforced With Ceramic Particles
Katarzyna N. Braszczyńska, Andrzej Bochenek Politechnika Częstochowska, Instytut Inżynierii Materiałowej, al. Armii Krajowej 19, 42-200 Częstochowa
Annals 1 No. 1, 2001 pages 28-31
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abstract While considering metal composites reinforced with ceramic particles, which are frequently obtained by casting, one cannot apply models developed for fibre composites to search for correlations, especially the ones involving mechanical properties. The relationships derived on basis of the additivity laws are not valid here, either for the assumption of constant stress or constant strain. Basic factors modelling the structure and properties of such composites, which should be selected while designing the specified material, are presented in Fig. 1. In the case of cast composites the greatest concern is given to the obtaining of the proper volume fraction of the particles within the matrix volume, the fraction being frequently corrected according to the actual one. Then the constant level of other factors is assumed for considering the composite. This leads to the neglecting of many dependent variables, the following being counted to them: • changes of chemical composition of the matrix caused by introduced particles or other additions (Fig. 2), • differences in the character of the joint between components, which greatly affect the obtained level of mechanical properties (Fig. 3), • uniformity (or the lack of it) of arrangement of the particles in the matrix, • changes in the matrix grain size due to introducing various volume fractions of ceramic particles of different size, • various degree of porosity (Fig. 4). Due to the presented numerous factors determining the structure of the cast metal composites reinforced with ceramic particles, reasons of frequently occurring inadequation of numerical models and experimental data seems to be obvious. After a series of analyses and experiments on composites reinforced with particles it seems that the most adequate model would be the one adopting Maxwell’s relationship between a parameter (a property) and the volume fraction, properties of components, and their interaction. This function shown in a general form by Eq. (1) has found rather strict confirmation in the results of experiments performed for Mg/SiC composites. Fig. 5 presents experimental data as compared with theoretical values obtained from Eq. (1) for tensile strength and yield strength versus SiC volume fraction.