Strengthening Effects of Multi-Walled Carbon Nanotubes and Graphene …
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damaging the structural integrity, and effective load transfer between the reinforcement and the metallic matrix, is essential to utilize the remarkable strengthening effect
of the reinforcement [17, 22, 23]. Previously, many investigations were performed to
utilize ball milling followed by spark plasma sintering technique to synthesize metal
matrix nanocomposites reinforced with uniformly dispersed carbonaceous reinforcement [12, 17, 24, 25]. The present research focuses on the feasibility of processing
carbon nanotubes reinforced nickel and Ni-GNP nanocomposites via high energy ball
milling followed by Spark plasma sintering consolidation to achieve uniform dispersion of carbonaceous reinforcement in the nickel matrix. Carbon nanotubes reinforced nickel metal matrix nanocomposites (Ni-CNT), and graphene nanoplatelets
reinforced nickel metal matrix composites (Ni-GNP) are processed using the same
processing route. The characterization of the microstructure and the mechanical
properties of the as processed composite samples was performed to investigate the
strengthening efficiency of CNTs and GNPs as reinforcement in the nickel matrix
composites.
Experimental Methods
Materials and Methods
The Ni-CNT nanocomposite powder is processed using the powder mixture of pure
nickel and 0.5wt%, 1wt%, and 2wt% of multi-walled carbon nanotubes (further
referred to as Ni-0.5CNT, Ni-1CNT, and Ni-2CNT). Nickel-coated multi-walled
carbon nanotubes were used instead of raw multi-walled carbon nanotubes to achieve
better dispersion of CNTs in the nickel matrix. The Ni-CNT nanocomposite is
obtained via a ball milling technique. The ball milling was performed in an argon
atmosphere with the ball to powder charge ratio of 10:1 for 6 h at a milling speed
of 200 rpm. The processed Ni-CNT composite powder was sintered using the spark
plasma sintering technique at a temperature of 800 °C for 5 min under a uniaxial
pressure of 65 MPa with a heating rate of 100 °C/min. A similar processing route
was utilized for processing graphene nanoplatelets reinforced in nickel matrix with
varying weight fraction (0.5, 1, 2 wt%) of the GNP reinforcement.
Characterization Techniques
The SPS processed Ni-CNT, and Ni-GNP composite samples were mechanically
polished subsequently with increasing grit size silicon carbide papers. The final
lustrous metallographic finish was obtained via polishing on 0.04 µm colloidal silica
before characterization. To investigate the effects of CNT/GNP content on its dispersion and the microstructure of the composites, a scanning electron microscope (SEM)
113
damaging the structural integrity, and effective load transfer between the reinforcement and the metallic matrix, is essential to utilize the remarkable strengthening effect
of the reinforcement [17, 22, 23]. Previously, many investigations were performed to
utilize ball milling followed by spark plasma sintering technique to synthesize metal
matrix nanocomposites reinforced with uniformly dispersed carbonaceous reinforcement [12, 17, 24, 25]. The present research focuses on the feasibility of processing
carbon nanotubes reinforced nickel and Ni-GNP nanocomposites via high energy ball
milling followed by Spark plasma sintering consolidation to achieve uniform dispersion of carbonaceous reinforcement in the nickel matrix. Carbon nanotubes reinforced nickel metal matrix nanocomposites (Ni-CNT), and graphene nanoplatelets
reinforced nickel metal matrix composites (Ni-GNP) are processed using the same
processing route. The characterization of the microstructure and the mechanical
properties of the as processed composite samples was performed to investigate the
strengthening efficiency of CNTs and GNPs as reinforcement in the nickel matrix
composites.
Experimental Methods
Materials and Methods
The Ni-CNT nanocomposite powder is processed using the powder mixture of pure
nickel and 0.5wt%, 1wt%, and 2wt% of multi-walled carbon nanotubes (further
referred to as Ni-0.5CNT, Ni-1CNT, and Ni-2CNT). Nickel-coated multi-walled
carbon nanotubes were used instead of raw multi-walled carbon nanotubes to achieve
better dispersion of CNTs in the nickel matrix. The Ni-CNT nanocomposite is
obtained via a ball milling technique. The ball milling was performed in an argon
atmosphere with the ball to powder charge ratio of 10:1 for 6 h at a milling speed
of 200 rpm. The processed Ni-CNT composite powder was sintered using the spark
plasma sintering technique at a temperature of 800 °C for 5 min under a uniaxial
pressure of 65 MPa with a heating rate of 100 °C/min. A similar processing route
was utilized for processing graphene nanoplatelets reinforced in nickel matrix with
varying weight fraction (0.5, 1, 2 wt%) of the GNP reinforcement.
Characterization Techniques
The SPS processed Ni-CNT, and Ni-GNP composite samples were mechanically
polished subsequently with increasing grit size silicon carbide papers. The final
lustrous metallographic finish was obtained via polishing on 0.04 µm colloidal silica
before characterization. To investigate the effects of CNT/GNP content on its dispersion and the microstructure of the composites, a scanning electron microscope (SEM)