Fabrication and effective thermal conductivity of multi-walled carbon nanotubes reinforced Cu matrix composites for heat sink applications
ABSTRACT A novel particles-compositing method was used for the first time to disperse different contents of multi-walled carbon nanotubes (CNTs) in micron sized copper powders, which were subsequently consolidated into CNT/Cu composites by spark plasma sintering (SPS). Microstructural observations showed that the homogeneous distribution of CNTs and dense composites could be obtained for 0–10 vol.% CNT contents. The CNT clusters were appeared in the powder mixture with 15 vol.% CNTs, which resulted in an insufficient densification of the composites. The effective thermal conductivity of the composites was analyzed both theoretically and experimentally. The addition of CNTs showed no enhancement in overall thermal conductivity of the composites due to the interface thermal resistance associated with the low phase contrast of CNT to copper and the random tube orientation. Besides, the composite containing 15 vol.% CNTs led to a rather low thermal conductivity due possiblely to the combined effect of unfavorable factors induced by the presence of CNT clusters, i.e. large porosity, lower effective conductivity of CNT clusters themselves and reduction of SPS cleaning effect. The CNT/Cu composites may be a promising thermal management material for heat sink applications.
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ABSTRACT: a b s t r a c t The thermal stability of ultrafine-grained (UFG) microstructures in pure copper samples and copper–car-bon nanotube (CNT) composites processed by High Pressure Torsion (HPT) was compared. The UFG microstructure in the sample consolidated from pure Cu powder exhibited better stability than that developed in a casted Cu specimen. The addition of CNTs to the Cu powder further increased the stability of the UFG microstructure in the consolidated Cu matrix by hindering recrystallization, however it also yielded a growing porosity and cracking during annealing. It was shown that the former effect was stron-ger than the latter one, therefore the addition of CNTs to Cu has an overall benefit to the hardness in the temperature range between 300 and 1000 K. A good agreement between the released heat measured dur-ing annealing and the calculated stored energy was found for all samples.Composites Part A Applied Science and Manufacturing 01/2013; 51:71–79. · 2.74 Impact Factor
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ABSTRACT: a b s t r a c t Highly thermally conductive graphite flakes (G f)/Si/Al composites have been fabricated using G f , Si pow-der and an AlSi 7 Mg 0.3 alloy by an optimized pressure infiltration process for thermal management appli-cations. In the composites, the layers of G f were spaced apart by Si particles and oriented perpendicular to the pressing direction, which offered the opportunity to tailor the thermal conductivity (TC) and coeffi-cient of thermal expansion (CTE) of the composites. Microstructural characterization revealed that the formation of a clean and tightly-adhered interface at the nanoscale between the side surface of the G f and Al matrix, devoid of a detrimental Al 4 C 3 phase and a reacted amorphous Al–Si–O–C layer, contributed to excellent thermal performance along the alignment direction. With increasing volume fraction of G f from 13.7 to 71.1 vol.%, the longitudinal (i.e. parallel to the graphite layers) TC of the composites increased from 179 to 526 W/m K, while the longitudinal CTE decreased from 12.1 to 7.3 ppm/K (match-ing the values of electronic components). Furthermore, the modified layers-in-parallel model better fitted the longitudinal TC data than the layers-in-parallel model and confirmed that the clean and tightly-adhered interface is favorable for the enhanced longitudinal TC.Materials and Design 07/2014; 63:719. · 2.91 Impact Factor
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ABSTRACT: Carbon nanotubes (CNTs) are incorporated into the Cu–Cr matrix to fabricate bulk CNT/Cu–Cr composites by means of a powder metallurgy method, and their thermal conductivity behavior is investigated. It is found that the formation of Cr3C2 interfacial layer improves the interfacial bonding between CNTs and Cu–Cr matrix, producing a reduction of interfacial thermal resistance, and subsequently enhancing the thermal conductivity of the composites. The thermal conductivity of the composites increases by 12 % and 17 % with addition of 5 vol.% and 10 vol.% CNTs, respectively. The experimental results are also theoretically analyzed using an effective medium approximation (EMA) model, and it is found that the EMA model combined with a Debye model can provide a satisfactory agreement to the experimental data.Applied Physics A 09/2013; 112(3). · 1.69 Impact Factor