A Comparative Study on the Effect of Graphene and Multi-walled …
145
weldability and aesthetics because of which this grade is widely used in various
industries. Also, because of the less amount of carbon present, carbide formation at
the grain boundaries during welding is negligible [9, 24]. The presence of graphene
nanoplatelets and multi-walled carbon nanotubes in an optimum amount in the weld
nugget is likely to escalate the weld properties and also other mechanical properties
owing to the high aspect ratio of multi-walled carbon nanotubes and the higher
restraining effect associated with them. Lap shear tests, followed by a detailed
weld nugget characterization, are to be performed to get an insight into the weld
strengthening mechanisms.
Experimental Details
Materials and Methods
Carbon steel (AISI-1008) steel plates with dimensions 95 × 19 × 0.85 mm were
used as the initial base materials. The chemical constituents and mechanical properties of AISI-1008 steel have been provided in Tables 1 and 2, respectively. Graphene
nanoplatelets, procured from United Nanotech Innovation Pvt. Ltd., had the average
size in X and Y direction as follows: 10–20 μm, average thickness: 3–6 nm, the
average number of layers: 6–10, parallel surface tensile modulus: >1000 GPa and
tensile strength: >5 GPa. Multi-walled carbon nanotubes were supplied by UnitedNanotech Ltd. with external size ~5 to 25 nm and average length variation between
1 and 10 μm, density ~0.30 g/cc, and specific surface area of 330 m
2 /g. Sodium
dodecyl sulfate (SDS) was used as a surfactant for dispersing the multi-walled carbon
nanotubes which was procured from Merck Emplura (M = 288.37 g/mol). Polyvinyl
alcohol (PVA) was purchased from LOBA Chemie with properties as degree of polymerization: 1700–1800, viscosity: 25–32cps, and pH (0.2% in water): 5–7. It is used
as a binder for both the carbon nanomaterials. The transmission electron micrographs of the as-received graphene nanoplatelets and multi-walled carbon nanotubes
are presented in Fig. 1a–b.
A schematic representation of the sample preparation method is illustrated in
Fig. 1c. Graphene nanoplatelets and multi-walled carbon nanotubes were finely
distributed in a PVA solution are drop-casted on the steel plates where spot welding
is carried out. Sodium dodecyl sulfate was used with multi-walled carbon nanotubes
as a surfactant for the easy dispersion. During the RSW process, these coatings were
used as the interlayers between the steel plates. To carry out the spot welding process,
an electrical resistance welding machine (ELECTROWELD SP30R, functioning at
415 V, 12 kA maximum short circuit current and maximum power output (at 50%
duty cycle) of 30 kVA, force: 1–4 kg/cm
2 ) was employed. Since the resistance of the
metal interface is relatively higher because of the presence of PVA bonded graphene
nanoplatelets and multi-walled carbon nanotubes, more heat is generated at these
locations where the interlayers (coating) are present. Preliminary experiments over
145
weldability and aesthetics because of which this grade is widely used in various
industries. Also, because of the less amount of carbon present, carbide formation at
the grain boundaries during welding is negligible [9, 24]. The presence of graphene
nanoplatelets and multi-walled carbon nanotubes in an optimum amount in the weld
nugget is likely to escalate the weld properties and also other mechanical properties
owing to the high aspect ratio of multi-walled carbon nanotubes and the higher
restraining effect associated with them. Lap shear tests, followed by a detailed
weld nugget characterization, are to be performed to get an insight into the weld
strengthening mechanisms.
Experimental Details
Materials and Methods
Carbon steel (AISI-1008) steel plates with dimensions 95 × 19 × 0.85 mm were
used as the initial base materials. The chemical constituents and mechanical properties of AISI-1008 steel have been provided in Tables 1 and 2, respectively. Graphene
nanoplatelets, procured from United Nanotech Innovation Pvt. Ltd., had the average
size in X and Y direction as follows: 10–20 μm, average thickness: 3–6 nm, the
average number of layers: 6–10, parallel surface tensile modulus: >1000 GPa and
tensile strength: >5 GPa. Multi-walled carbon nanotubes were supplied by UnitedNanotech Ltd. with external size ~5 to 25 nm and average length variation between
1 and 10 μm, density ~0.30 g/cc, and specific surface area of 330 m
2 /g. Sodium
dodecyl sulfate (SDS) was used as a surfactant for dispersing the multi-walled carbon
nanotubes which was procured from Merck Emplura (M = 288.37 g/mol). Polyvinyl
alcohol (PVA) was purchased from LOBA Chemie with properties as degree of polymerization: 1700–1800, viscosity: 25–32cps, and pH (0.2% in water): 5–7. It is used
as a binder for both the carbon nanomaterials. The transmission electron micrographs of the as-received graphene nanoplatelets and multi-walled carbon nanotubes
are presented in Fig. 1a–b.
A schematic representation of the sample preparation method is illustrated in
Fig. 1c. Graphene nanoplatelets and multi-walled carbon nanotubes were finely
distributed in a PVA solution are drop-casted on the steel plates where spot welding
is carried out. Sodium dodecyl sulfate was used with multi-walled carbon nanotubes
as a surfactant for the easy dispersion. During the RSW process, these coatings were
used as the interlayers between the steel plates. To carry out the spot welding process,
an electrical resistance welding machine (ELECTROWELD SP30R, functioning at
415 V, 12 kA maximum short circuit current and maximum power output (at 50%
duty cycle) of 30 kVA, force: 1–4 kg/cm
2 ) was employed. Since the resistance of the
metal interface is relatively higher because of the presence of PVA bonded graphene
nanoplatelets and multi-walled carbon nanotubes, more heat is generated at these
locations where the interlayers (coating) are present. Preliminary experiments over