Mechanical and thermal properties of carbon nanotube/aluminum composites consolidated by spark plasma sintering

Abstract

Aluminum matrix composites reinforced with 0–5.0 wt.% multi-walled carbon nanotubes (MWNTs) were produced by spark plasma sintering (SPS). The composites with ⩽1.0 wt.% MWNTs additions had higher thermal conductivity than the pure aluminum produced by the same SPS processing. The MWNTs/Al composites exhibited the maximum thermal conductivity of 199 W/m/K at 0.5 wt.% MWNTs. The enhancement of thermal conductivity is supported by the measured tensile strength. The MWNTs/Al composites exhibited the maximum tensile strength of 130 MPa also at 0.5 wt.% MWNTs. The contribution of carbon nanotubes to thermal conductivity of the composites was demonstrated by theoretical analysis. The results show that MWNTs reinforced aluminum matrix composite is a potential material for high thermal conductivity applications.

Introduction

Metal matrix composites (MMCs) with enhanced thermal conductivities have received substantial attention for packaging materials applications such as microelectronics and optical communications [1], [2], [3], [4]. Carbon nanotubes (CNTs) are one of novel reinforcements for composites due to their remarkable mechanical and thermal properties [5], [6], [7], [8], [9]. According to theoretical predictions and experimental measurements, the thermal conductivity of CNTs reaches as high as 3000–6600 W/m/K [10], [11]. Aluminum is one of the most important matrix materials for MMCs. Mechanical properties of CNTs reinforced Al matrix composites (CNTs/Al composites) have been intensively studied.

So far only a few reports have dealt with thermal conducting behavior of CNTs/Al composites. Bakshi et al. [12] produce a 10 wt.% CNTs/Al composite using plasma spraying and report a thermal conductivity of just 25.4 W/m/K, much less than that of pure Al. Yamanaka et al. [13] report that the thermal conductivity of CNTs/Al composites is decreased with increasing CNT content. Thermal conductivity reported for CNTs/Cu composites [14], [15] also shows a decreasing tendency compared with pure Cu. The thermal conductivity decline is mainly associated with CNTs agglomeration that has introduced thermal interface barriers into the composites. Two requirements should be satisfied in order to achieve high thermal conductivity in CNTs/metal composites – the composites have low interfacial thermal resistance and CNTs are homogeneously dispersed in metal matrix. The present study focuses on the thermal conducting behavior of aluminum matrix composites reinforced with multi-walled carbon nanotubes (MWNTs/Al composites) that are produced by spark plasma sintering (SPS). The SPS processing is a very useful technique for densifying unsinterable materials such as carbon nanotubes. Sound interfacial bonding between reinforcements and matrix can also be formed by strong spark plasma [5]. In order to generate homogeneous dispersion of carbon nanotubes in aluminum matrix, the powder mixture is carefully modified before SPS processing.

The purpose of this paper is to demonstrate the enhancement of both tensile strength and thermal conductivity by dispersing MWNTs in Al matrix. Theoretical models are combined to examine the contribution of dispersed carbon nanotubes to thermal conducting. It also suggests that the thermal conductivity of MWNTs/Al composites is reduced again by adding >1.0 wt.% MWNTs, owing to the difficulty in dispersing high fraction carbon nanotubes.