Carbon-nanotube-length dependent interfacial reaction in aluminum matrix composites and its effect on strengthening

The interfacial reaction is a critical factor affecting the strengthening effect of carbon nanotubes (CNTs) in metal matrix composites . In this work, the effects of CNT length on the morphology and formation mechanism of interfacial aluminum carbide (Al 4 C 3 ) in aluminum (Al) matrix composites were investigated. By observing a vast number of Al 4 C 3 in Al composites which were reinforced with CNTs by different aspect ratios, three kinds of morphologies (skinny, twinned and chunky) were identified. Analyses on intermediate reaction products of these three kinds of Al 4 C 3 revealed that their length increased with the increase of CNT length, but their morphologies had a weak relationship with CNT length. The morphologies were determined by the dispersion state of CNTs, the nucleation sites of Al 4 C 3 and element diffusion modes. Both the two debating mechanisms for Al 4 C 3 formation, viz., carbon-atom-diffusion mechanism and carbon-template-growth mechanism, were confirmed for the rod-shaped skinny and twinned Al 4 C 3 , respectively. Chunky Al 4 C 3 shared a similar formation mechanism with twinned Al 4 C 3 while it formed at CNT cluster. The growing process and strengthening effects of the three kinds of interfacial Al 4 C 3 with different lengths were thoroughly discussed. This study may provide guidance to control the interface in nano-carbon-reinforced Al matrix composites for superior properties. The formation mechanisms brief diagram of various Al 4 C 3 morphologies (skinny, chunky and twinned) in CNTs/Al composite. • The relationship between original CNTs length and Al 4 C 3 has been concluded. • Revealed the nucleation and growth mechanism of various interfacial Al 4 C 3 . • Clarifying the relationship between disregistry of interface and element diffusion modes. • Affirmed five types of orientation relationships in the Al–Al 4 C 3 interface. • The strengthening effects of Al 4 C 3 with different morphologies are discussed.