An Investigation on the Sinterability and the Compaction Behavior of Aluminum/Graphene Nanoplatelets (GNPs) Prepared by Powder Metallurgy A. Saboori, C. Novara, M. Pavese, C. Badini, F. Giorgis, and P. Fino (Submitted September 6, 2016; in revised form November 15, 2016) In the present study, the densification response of Al matrix reinforced with different weight percentages (0, 0.5, 1.0, 1.5 and 2.0 wt.%) of graphene nanoplatelets (GNPs) was studied. These composites were produced by a wet method followed by a conventional powder metallurgy. The Raman spectrum of graphene indi- cates that preparation of the composites through the wet mixing method did not affect the disordering and defect density in the GNPs structure. The nanocomposite powder mixture was consolidated via a cold uniaxial compaction. The samples were sintered at different temperatures (540, 580 and 620 °C) under nitrogen flow so as to assess the sinterability of the nanocomposites. X-ray diffraction (XRD) has been carried out to check the possible reaction between GNPs and aluminum. According to the XRD patterns, it seems that Al 4 C 3 did not form during the fabrication process. The relative density, compressibility, sin- terability and Vickers hardness of the nanocomposites were also evaluated. The effects of GNPs on the consolidation behavior of the matrix were studied using the Heckel, Panelli and Ambrosio Filho, and Ge equations. The outcomes show that at early stage of consolidation the rearrangement of particles is dom- inant, while by increasing the compaction pressure, due to the load partitioning effect of GNPs, the densification rate of the powder mixture decreases. Moreover, the fabricated nanocomposites exhibited high Vickers hardness of 67 HV 5 , which is approximately 50% higher than monolithic aluminum. The effect of graphene addition on the thermal conductivity of Al/GNPs nanocomposites was evaluated by means of thermal diffusivity measurement, and the results showed that the higher thermal conductivity can be only achieved at lower graphene content. Keywords aluminum, compaction, GNPs, sinterability, thermal conductivity 1. Introduction In general, aluminum matrix nanocomposites can be produced through different techniques such as casting, powder metallurgy (PM), or additive manufacturing (AM) (Ref 1). While casting and additive manufacturing techniques are more interesting due to design and economic reasons, PM attracts attention because of its lower fabrication temperature with respect to the others. As a consequence of lower temperature of manufacturing process, the destructive interfacial reaction between Al matrix and the reinforcement, in particular in the case of carbon-based reinforcements, is prevented (Ref 2-5). Another important merit of PM over casting is the homoge- neous dispersion of reinforcement in the matrix in such a way that through the PM route it is feasible to obtain a uniform dispersion of the second phase even at higher volume fractions of reinforcement (Ref 6-8). Graphene nanoplatelets (GNPs) are nanoscale reinforcement that show superior mechanical, electrical, and thermal proper- ties (Ref 8). However, the dispersion of GNPs in the aluminum matrix is a great challenge due to their poor dispersion and formation of agglomerates in the Al matrix. In previous studies, it was reported that mechanical alloying could be a suitable technique to disperse the nanoparticles inside the matrix but it is not a good option to disperse the GNPs because it damages their structure (Ref 8). Saboori et al. (Ref 9) have proposed a wet method as an alternative technique for the dispersion of GNPs in Al matrix. One of the key steps in PM is consolidation, which can affect the final properties (density, microstructure, and mechanical properties) of the composite. The easiest and most conventional way to consolidate the powder into a bulk component is unidirec- tional compaction at ambient temperature followed by sinter- ing under a controlled atmosphere (Ref 10, 11). Thus, studying the compaction behavior of Al in presence of any reinforcement under different compaction pressures is of great interest. Many compaction equations such as Balshin and Mettalprom (Ref 12), Heckel (Ref 13), Walker (Ref 14), Copper-Eaton (Ref 15), Kawakita (Ref 16), Panelli and Ambrosio Filho (Ref 17), and Ge (Ref 18) have been reported to predict the relative density at a given applied pressure. The metal powder consolidation has been studied through a number of theoretical and analytical models as well. For example, the densification rate of porous materials was modeled by Doraivelu et al. (Ref 19) and a micromechanical model has been developed to study the effect of particle content on relative density and isostatic compaction (Ref 20- 23). Thereafter, similar models have been developed by Fleck et al. (Ref 24, 25) for non-isostatic compaction. A. Saboori, C. Novara, M. Pavese, C. Badini, F. Giorgis, and P. Fino, Department of Applied Science and Technology, Politecnico Di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. Contact e-mail: abdollah.saboori@polito.it. JMEPEG ÓASM International DOI: 10.1007/s11665-017-2522-0 1059-9495/$19.00 Journal of Materials Engineering and Performance