Sintering Behaviors of Carbon Nanotubes—Aluminum Composite Powders

Biao Chen,Katsuyoshi Kondoh

doi:10.3390/met6090213

Abstract

Carbon nanotubes (CNTs) are promising reinforcements for fabricating aluminum (Al) matrix composites with outstanding properties. The understanding of the consolidation process of CNT–Al composite powders plays a significant role in achieving high performances of bulk composites. In this study, an advanced consolidation technique of spark plasma sintering (SPS) was used to fabricate CNT–Al composites with homogeneously dispersed CNTs. The sintering kinetics of pure Al powders and those powders coated with 1 wt % CNTs were studied. By combining the electrical conductivity and relative density results, it was found that the sintering process consisted of two stages with distinct densification rates. The second stage with a much lower rate was governed by the breaking down of alumina films at primary particle boundaries. The activation energy of the controlling second stage increased by 55% in CNT–Al composite powders compared to that of pure Al powder. As a result, CNT addition led to the overall decrease of sintering ability, which raised a challenge in the processing of CNT–Al composites.

Highlights

Carbon nanotubes (CNTs), including multi-walled CNTs and single-walled CNTs, have attracted great attention in materials science since the landmark report by Iijima in 1991 [1]
The sintering behaviors of ball milled pure Al powders and those powders coated with well-dispersed CNTs were studied using the Arrhenius law
The sintering process consisted of two stages with distinct densification kinetics, agreeing with the tendencies of electrical conductivities

Summary

Introduction

Carbon nanotubes (CNTs), including multi-walled CNTs and single-walled CNTs, have attracted great attention in materials science since the landmark report by Iijima in 1991 [1]. Due to the outstanding structural and physical properties, such as large aspect ratios, high strength, and high electrical/thermal conductivities, CNTs are regarded as promising reinforcements for composites [2]. In the past decade, increasing attention was paid to CNT reinforced metal matrix composites (MMCs), which were expected as next-generation strong materials [3]. Special interests were paid to aluminum (Al) matrix composites (AMCs) because their high specific strength, high conductivities, and anti-corrosive properties made them promising structural materials in aerospace, automobile, and sports industries [4]. To achieve high load transfer efficiency [5] in CNT–Al composites, suitable processing approaches should be explored. A homogeneous CNT dispersion in composites is the precondition, because there is little bonding between matrix and the CNTs inside CNT clusters, which is detrimental for effective load transfer [6]. A high relative density is the first consideration, because it is the prime requirement for effective

Methods

Discussion

Conclusion