Thermal Conductivity and Tensile Properties of Carbon Nanofiber-Reinforced Aluminum-Matrix Composites Fabricated via Powder Metallurgy: Effects of Ball Milling and Extrusion Conditions on Microstructures and Resultant Composite Properties

doi:10.1007/s40195-018-0811-8

Abstract

Abstract:

Carbon nanofiber (CNF)-reinforced aluminum-matrix composites were fabricated via ball milling and spark plasma sintering (SPS), SPS followed by hot extrusion and powder extrusion. Two mixing conditions of CNF and aluminum powder were adopted: milling at 90 rpm and milling at 200 rpm. After milling at 90 rpm, the mixed powder was sintered using SPS at 560 °C. The composite was then extruded at 500 °C at an extrusion ratio of 9. Composites were also fabricated via powder extrusion of powder milled at 200 rpm and 550 °C with an extrusion ratio of 9 (R9) or 16 (R16). The thermal conductivity and tensile properties of the resultant composites were evaluated. Anisotropic thermal conductivity was observed even in the sintered products. The anisotropy could be controlled via hot extrusion. The thermal conductivity of composites fabricated via powder extrusion was higher than those fabricated using other methods. However, in the case of specimens with a CNF volume fraction of 4.0%, the thermal conductivity of the composite fabricated via SPS and hot extrusion was the highest. The highest thermal conductivity of 4.0% CNF-reinforced composite is attributable to networking and percolation of CNFs. The effect of the fabrication route on the tensile strength and ductility was also investigated. Tensile strengths of the R9 composites were the highest. By contrast, the R16 composites prepared under long heating duration exhibited high ductility at CNF volume fractions of 2.0% and 5.0%. The microstructures of composites and fracture surfaces were observed in detail, and fracture process was elucidated. The results revealed that controlling the heating and plastic deformation during extrusion will yield strong and ductile composites.

Key words: Al composite, Carbon nanofiber, Ball milling, Hot extrusion, Microstructure and performance

Fumio Ogawa, Shuji Yamamoto, Chitoshi Masuda. Thermal Conductivity and Tensile Properties of Carbon Nanofiber-Reinforced Aluminum-Matrix Composites Fabricated via Powder Metallurgy: Effects of Ball Milling and Extrusion Conditions on Microstructures and Resultant Composite Properties[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(5): 573-584.

Figures/Tables 25

Fig. 1 SEM image of CNFs

Fig. 2 SEM image of inside mixed powder of CNFs and aluminum with CNF volume fraction of 1.0% after ball milling at 90 rpm

Fig. 3 Planes for thermal conductivity measurements

Table 1 Fabrication conditions of CNF-reinforced aluminum-matrix composites

Fabrication route	Ball-milling conditions	SPS and/or hot extrusion condition
SPS	90 rpm, 3 h, ball-to-weight ratio = 20:1 (aluminum particle size: 3 μm)	SPS: 560 °C, 2 h, 50 MPa
SPS and hot extrusion	90 rpm, 3 h, ball-to-weight ratio = 20:1 (aluminum particle size: 3 μm)	SPS: 560 °C, 2 h, 50 MPa Hot extrusion: 500 °C, 0.1 mm/min, R9
Powder extrusion	200 rpm, 3 h, ball-to-weight ratio = 20:1 (aluminum particle size: 30 μm)	Powder extrusion: 550 °C, 20 mm/min, R9 (holding time: 0.5 h), R16 (holding time: 1.5 h)

Fig. 4 Thermal conductivities of the sintered CNF-aluminum composites in the directions perpendicular to the T and P planes as a function of the CNF volume fraction

Fig. 5 SEM images of the sintered 1.0% CNF-reinforced composites: a T plane, b P plane

Fig. 6 Thermal conductivities of CNF-aluminum composites fabricated via SPS followed by hot extrusion, plotted as a function of the CNF volume fraction

Fig. 7 XRD patterns of 4.0% CNF-aluminum composites fabricated via extrusion followed by sintering

Fig. 8 SEM image obtained on the P plane of the 0.5% CNF-aluminum composite fabricated by extrusion after sintering

Fig. 9 Thermal conductivities of composites fabricated by powder extrusion, SPS, and hot extrusion in conjunction with SPS

Fig. 10 SEM image of a 1.0% CNF-reinforced composite fabricated by powder extrusion

Fig. 11 Nominal stress-nominal strain curve of the 0.5% CNF-aluminum composite fabricated by SPS and hot extrusion; the corresponding curve for pure aluminum is also shown

Fig. 12 SEM images of the fracture surface of the 0.5% CNF-aluminum composite fabricated by SPS and hot extrusion

Fig. 13 True stress-true strain curves of composites fabricated by powder extrusion with an extrusion ratio of 9

Fig. 14 Fracture surface of 0.5% CNF-reinforced composites fabricated by powder extrusion with an extrusion ratio of 9

Fig. 15 FESEM image of aluminum grains in 0.5% CNF-aluminum composites fabricated by powder extrusion at an extrusion ratio of 9

Fig. 16 True stress-true strain curves of composites fabricated by powder extrusion with an extrusion ratio of 16

Fig. 17 Fracture surfaces of aluminum materials fabricated by powder extrusion with an extrusion ratio of a 16, b 9

Fig. 18 Comparison of true stress-true strain curves of 2.0% CNF-aluminum composites fabricated by powder extrusion with extrusion ratios of 9 and 16

Fig. 19 Fracture surface of 2.0% CNF-aluminum composites fabricated by powder extrusion with extrusion ratio of 9

Fig. 20 FESEM image of aluminum grains in 2.0% CNF-aluminum composites fabricated by powder extrusion at extrusion ratio of 9

Fig. 21 FESEM image of aluminum grains in 2.0% CNF-aluminum composites fabricated by powder extrusion at extrusion ratio of 9 at a different position from Fig. 20

Fig. 22 Fracture surface of 2.0% CNF-aluminum composites fabricated by powder extrusion with an extrusion ratio of 16

Fig. 23 FESEM image of aluminum grains in 2.0% CNF-aluminum composites fabricated by powder extrusion at an extrusion ratio of 16

Fig. 24 FESEM image of aluminum grains in 2.0% CNF-aluminum composites fabricated by powder extrusion at an extrusion ratio of 16 in a different position from Fig. 23

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