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Abstract
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The effects of the size and morphology of the reinforcement phases on the hardness and tribological behavior of the AZ31 Mg alloy matrix composites were investigated. Three different ceramic particles including boron carbide (B4C), tungsten carbide (WC), and Zirconia (ZrO2) were selected as the reinforcement materials. The average sizes of the B4C, WC and ZrO2 particles were about 150 μm, 5 μm, 35 nm, respectively. Mono reinforced composites, including AZ31/B4C, AZ31/WC, and AZ31/ZrO2, were developed using friction stir processing (FSP) technique. Moreover, to study the effect of hybrid reinforcements on the characteristics mentioned above, the AZ31/B4C+ZrO2 and AZ31/WC+ZrO2 hybrid composites were also fabricated by the same method. Secondary electron microscopy (SEM) analyses of the composites showed a homogenous distribution of the reinforcement particles in the Mg alloy matrix. Microhardness measurements revealed that the hardness of AZ31/ZrO2 nanocomposite increased about 120% regarding the AZ31 base metal. According to the results of the dry sliding wear tests, among the mono reinforcement composites, the AZ31/B4C and AZ31/ZrO2 had the maximum wear resistance and the minimum average of friction coefficient, respectively. Hybridization of reinforcements with the ZrO2 nanoparticles caused an improvement in both wear resistance and friction performance of the composites. SEM observation of the worn surfaces and debris resulted from wearing of the samples after 500 m sliding distance under the applied normal load of 10 N, revealed that the severe and mild abrasive wear were the dominant mechanisms governed in the composites.
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