In the present work, an indigenously developed low cost modified stir casting technique is developed for the processing of 6061 Al‐B4C composites containing high‐volume fraction of boron carbide particles (up to 20 vol. %). The influence of varying reinforcement content on the spatial distribution of boron carbide in the aluminum matrix is qualitatively characterized using scanning electron microscope. At a lower volume fraction of reinforcement, wide particle free zone and large interparticle spacing were observed in the matrix while the composite with high reinforcement content displayed relatively homogeneous and discrete particle distribution. X‐ray diffraction analysis confirms the presence of only aluminum and boron carbide diffraction peaks, indicating that no significant reaction occurs during composite processing. The tensile behavior of composites revealed that strength and ductility are influenced by varying particulate content. The quantitative analysis of strengthening mechanism in the casted composites showed that higher volume fraction of boron carbide lead to larger values of thermal dislocation strengthening, grain size and strain gradient strengthening. The morphology of fracture surfaces reveals the presence of dimple network and the average size of dimples gradually decreases with the increase in particulate content, which indicates the co‐existence of ductile and brittle fracture.
In the present work, 6061 Al–B4C metal matrix composites with different volume fractions (5, 10, 15 and 20 vol.%) have been fabricated by a low cost modified stir casting technique. The effect of varying particulate content on the microstructure of Al–B4C composites has been qualitatively characterized using a scanning electron microscope and an optical microscope. Tensile tests were performed to study the influence of varying reinforcement content on the strengthening behavior of fabricated composites. The composite’s yield strength increases significantly as the B4C content was increased from 0 to 20 vol.%. The enhancement in strength was elucidated on the basis of strengthening mechanisms characterized by load transfer, thermal dislocation, grain size, and strain gradient strengthening. The strengthening mechanisms were quantitatively analyzed and evaluated as a function of particle size and volume fraction. A critical particle size was found to be about 45 µm, below which the strengthening contributions from different mechanism increases remarkably. At a higher volume fraction of B4C, the effect of thermal dislocation strengthening becomes more dominant as compared to other mechanisms. Furthermore, the analytical models proposed by Ramakrishnan and Chen for predicting the yield strength of particulate reinforced metal matrix composites have been extended to take into account the contribution of strain gradient effect in the strengthening mechanism of composites.
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