Fabrication method, microstructural characteristics, and hardness behavior of an interpenetrating phases hybrid aluminum/alumina-nanodiamond composite

Abstract

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. In 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 the 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 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 strengthening mechanisms for these composites are the Orowwn mechanism (volume fraction of ND particles) and the Hal-Petch mechanism (grain size), which affect the hardness behavior.

Keywords

• aluminum-matrix composite
• interpenetrating phases
• nanodiamond
• microstructure
• hardness