Carbon nanotube induced microstructural characteristics in powder metallurgy Al matrix composites and their effects on mechanical and conductive properties

In this study, Al matrix composites (AMCs) containing different contents (0–1 vol.%) of carbon nanotubes (CNTs) were fabricated by powder metallurgy (PM). A mechanical mixing process was used to disperse CNTs in Al powders. The powder mixtures were consolidated by spark plasma sintering and subsequent hot-extrusion. The microstructures, tensile properties, electrical conductivity (E.C.) and thermal conductivity (T.C.) of CNT/Al composites were examined. Within 0.75 vol.%, CNTs could be well dispersed and aligned in Al matrix. However, 1 vol.% CNTs led to agglomerations and resultant degraded tensile properties. With CNT additions, Al grains were refined under the pinning effect of CNTs at grain boundaries. An oxygen-rich layer was observed at PM CNT-Al interfaces by combination of transmission electronic microscopy and energy dispersive spectrometer analysis. The oxygen-rich layer was favorable to improve the bonding conditions between CNTs and Al matrix, leading to CNT fracture during composite failure. The refined grains and oxygen-rich interfaces were responsible for the improvement of tensile strength, but decreases of E.C. and T.C. of CNT/Al composites. Considering the CNT induced microstructure characteristics, grain & interface modified models were further set up. They showed good predictions on both the tensile strength and conductivity of CNT/Al composites. The results might provide new insights for designing simultaneously strong and high-conductivity metal matrix composites. - Highlights: • Microstructural, mechanical and conductive properties of CNT/Al were studied. • Refined grains and oxygen-rich (OR) interfaces were observed in CNT/Al composites. • Refined grains and OR interfaces led to improved strength but decreased conductivities. • Grain & interface modified models were set up to predict YS and T.C. of CNT/Al.