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The present study investigates the effect of multi-walled carbon nanotubes (MWCNTs) on atomic diffusion processes in the metal matrix, by comparing growth kinetics of interfacial phases in Al–Cu and Al/MWCNT–Cu diffusion couples. Multiple intermetallic layers such as Al2Cu, AlCu, Al3Cu4, Al2Cu3, and Al4Cu9 are formed at the interface between Al and Cu during heat treatment of an Al/Cu diffusion couple at 530℃. For the diffusion couple of ultrafine-grained Al and cast Cu, the growth rate of intermetallic layers is comparable with theoretical expectations based on Fick’s second law. On the other hand, MWCNTs significantly restrict the diffusion of Al atoms in the composite because the atoms tend to detour around the long tube for diffusion, particularly when MWCNTs are oriented perpendicular to the atomic diffusion path. This accelerates the growth of voids at the contact interface of the diffusion couple during heat treatment. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we investigate the effects of the size and volumetric fraction of Zr2Cu on the density and mechanical strength of liquid-reactive sintered W/MWCNTs/ Zr2Cu composites. Composite powders are formed by mechanical ball-milling and are sintered into a high density composite at 1400°C. During sintering, two major reactions occur: 1) C atoms in the MWCNTs reacted with the W matrix to form WC; 2) Zr in the Zr2Cu liquid phase, which flows through the capillaries between particles, reacts with WC in the W matrix to form ZrC. Based on our results, higher density composites with finer ZrC reinforcements are successfully produced using sub-micron size Zr2Cu powders. In addition, the amount of Zr2Cu is varied, and the optimal volumetric fraction of Zr2Cu that maximizes the hardness of the composite (1180Hv) is equal to 30vol.%. When the Zr2Cu content is less than the critical value, and the density of the composite is too low due to an insufficient amount of liquid. The hardness of the composite decreases when the Zr2Cu content is greater than 30vol.%, because excess liquid yields a network structure of WC, ZrC, and Zr. The experimental results also reveal that the sintering time required to reach the maximum hardness (1180Hv) significantly decreases as the size of Zr2Cu is reduced from micron-scale to nano-scale. [Copyright &y& Elsevier]