Document Type : Research Article
Department of Materials Engineering, Faculty of Engineering, University of Sistan and Baluchestan, Zahedan, Iran
In the present work, the addition effects of nanodiamond (ND) on the microstructure and hardness behavior of interpenetrating phases hybrid Al/Al2O3 metal matrix composites were investigated. The fabrication of the composites was done via a two-step process. At the first step, hybrid Al2O3-ND preforms were prepared and then molten pure Al alloy was infiltrated into the preforms. The preforms were fabricated by the replica method using a polyurethane foam and an Al2O3-ND slurry with various ND contents (0, 1, 3, and 10 vol%). The preforms were sintered at 1500 °C for 4 h under argon gas protection. Finally, the composites were fabricated by Al melt infiltration into the preforms via squeeze casting method. The microstructure of the fabricated composites was analyzed using optical and scanning electron microscopes. The hardness of the composites was measured using a Vickers hardness tester. The results of the microstructural evaluations demonstrated a good distribution of ND in the preform. By increasing the ND content from 0 to 10 vol%, the matrix average grain size has decreased from 143 μm to 76 μm. The results of the Vickers hardness test showed that increasing the volume percentage of ND increased the composite hardness to 263.8 Vickers at 10 vol%. The two main strengthen mechanisms for these composites are Orowwn mechanism (volume fraction of ND particles) and Hal-Petch mechanism (grain size), affecting the hardness behavior.