This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Metal matrix nanocomposites (MMNCs) are thosemetal matrix composites where the reinforcement is of nanometer dimensions, typically less than 100nm in size. Also, it is possible to have both the matrix and reinforcement phases of nanometer dimensions. The improvement in mechanical properties of MMNCs is attributed to the size and strength of the reinforcement as well as to the fine grain size of the matrix. Spark plasma sintering has been used extensively over the past years to consolidate wide range of materials including nanocomposites and was shown to be effective noneconventional sintering method for obtaining fully dense materials with preserved nanostructure features. The objective of this work is to briefly present the spark plasma sintering process and review published work on spark-plasma-sintered metals and metal matrix nanocomposites.

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Spark plasma sintering of metals and metal matrix nanocomposites: a review

Multiwalled carbon nanotubes as a contributing reinforcement phase for the improvement of thermal conductivity in copper matrix composites

On the role of amorphous intergranular and interfacial layers in the thermal conductivity of a multi-walled carbon nanotube-copper matrix composite

Physicomechanical properties of spark plasma sintered carbon nanotube-reinforced metal matrix nanocomposites

Multiwall carbon nanotube (MWNT) materials are attractive because they possess excellent thermal conductivity and mechanical properties. However, few reports exist that focus on improving the thermal conductivity of MWNT by combining it with a metal matrix. Thus to improve the thermal conductivity, a nickel-matrix composite with MWNT was prepared by slurry mixing process using ethanol as a solvent. Using spark plasma sintering (SPS), MWNT/Nickel nanocomposites were fabricated and the fabrication conditions were investigated. The sintered relative densities of the composites containing up to 5 vol% of MWNT were above 99%. The thermal and electrical behaviors of the MWNT/Nickel composites were determined using the laser flash and van der Pauw methods, respectively, and were found to be anisotropic. The thermal conductivity was found to increase by 10% for the composition with 3 vol% MWNT.

https://www.jstage.jst.go.jp/article/matertrans/48/9/48_MRA2007084/_pdf

Fabrication and Thermal Properties of Carbon Nanotube/Nickel Composite by Spark Plasma Sintering Method

Carbon nanotubes (CNT) have superior mechanical properties and high thermal conductivity. For such reasons, the development of CNT-metal matrix composite is gaining wide research attention. In this study, Al/CNT composite was fabricated by powder metallurgy employing the slurry mixing process and Spark Plasma Sintering (SPS) to overcome fabrication problems like agglomeration, which leads to the decrease in thermal conductivity and density.Slurry precursors with homogeneously dispersed CNT were obtained by hetero-aggregation, with optimum amount of ethanol. By sintering these precursors, the composites densified up to more than 99% in relative density. Dispersion and orientation of CNTs were verified by FE-SEM observation of microstructure. The thermal conductivity of the composites decreased with increasing CNT content, and the corresponding thermal anisotropies are indicated. The thermal properties are improved by extending the holding time during sintering.

Fabrication and thermal evaluation of carbon nanotube/aluminium composite by spark plasma sintering method

Carbon nanotube (CNT) has excellent feature like low density, high strength, and high thermal conductivity. The metal-based CNT composite is expected as a light and high strength material or the heat radiation material for the application to automobile and aircraft parts, etc. Such that the development of CNT-metal matrix composite is gaining wide research attention. Since CNTs are easy to agglomerate, however, it is difficult to disperse them into a metal matrix homogeneously. To overcome these problems, in this study, CNT-Nickel matrix composite was fabricated by using hetero aggregation and spark plasma sintering method.   Slurry precursors with homogeneously dispersed CNT were obtained, with optimum in amount of ethanol. The composites were densified up to more than 99% of relative density by sintering these precursors. Additionally, dispersion and orientation of CNTs were verified by FE-SEM observation of microstructure. The thermal conductivity of the composite was increased by about 10% or less at room temperature. Thermal anisotropy were indicated.

Thermal Properties of Carbon Nanotube/Nickel Composites Fabricated by Hetero Aggregation

Fabrication and thermal properties of carbon nanotube/nickel composite by spark plasma sintering method

Carbon nanotubes (CNT) have many interesting properties such as high thermal conductivity. Therefore, Cu/CNT composites are expected to be applied as heat sink material with good thermal properties.In this study, Cu/CNT precursor in which CNT distributed homogeneously was fabricated by colloidal process, and homogeneous distribution of CNT in Cu matrix was also observed in Cu/CNT composites sintered by spark plasma sintering (SPS). According to the analysis of gas generated from high-temperature precursor, structural defect of CNT, and oxygen content, SPS proved useful to reduce CNT's structural defects compare to conventional sintering methods. Using SPS in vacuum atmosphere, composites can be successfully formed with low temperature in short time. Existence of amorphous layer at Cu/CNT and Cu/Cu interface was observed by FETEM.

Shunsuke Yamanaka

Papers

Fabrication and Thermal Properties of Carbon Nanotube/Nickel Composite by Spark Plasma Sintering Method

Fabrication and thermal evaluation of carbon nanotube/aluminium composite by spark plasma sintering method

Thermal Properties of Carbon Nanotube/Nickel Composites Fabricated by Hetero Aggregation

Fabrication and thermal properties of carbon nanotube/nickel composite by spark plasma sintering method

Thermal conductivity of carbon nanotube/copper composites fabricated by colloidal process