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T. Das
Characterisation Methods
For characterization purposes, the bare, graphene nanoplatelets-coated and multiwalled carbon nanotubes-coated samples of 19 × 5 × 1.85 mm were cut along the
weld nugget and normal to the specimen plane using Elektra Maxicut Wire Electric
Discharge Machine (EDM). The samples were then polished in sequence by various
emery paper grades and finally with a 0.25 and 1 μ grit diamond paste. Nital (97 ml
ethanol + 3 ml HNO 3 ) etchant was used for revealing the grains of steel and other
nanoparticles in the weld nugget. Scanning electron microscopy (SEM) and energy
dispersive spectroscopy (EDS) were done using EVO 18 Research ZEISS-SEM. The
study of strengthening mechanisms and IMCs was done using JEOL, JEM2100F field
emission gun-transmission electron microscope (FEG-TEM) functioning at 200 kV.
Mechanically thinned samples (70 μm thick) were used, and a hole was created at
the centre of the samples by precision ion miller (GATAN, model 691).
X-Ray (XRD) was performed using EMPYREAN PAN-alytical DY1705 X’PERT
PRO XRD with CuKα and a range of 20°–120°. The analysis was carried out on the
graphene nanoplatelets and multi-walled carbon nanotubes-coated interlayered fractured cross-sectional samples processed at the best welding current/time conditions.
The information obtained was evaluated using X-pert high-score software. Raman
spectroscopy was performed to investigate the stresses experienced by the nanoparticles (graphene nanoplatelets, multi-walled carbon nanotubes) on the processed
samples, and for this, JOBIN-YVON-HORIBA (T6400) equipped with Ar–Kr laser
(at wavelength λ = 514 nm) was used.
Lap shear experiments were conducted using servo-hydraulic operated INSTRON
(8800 MK3305) Universal Testing Machine with 1 mm/min crosshead speed and
ambient temperature for the welded samples under various current/time settings.
Fracture surface analysis was done at altered magnifications. Microhardness test (Hv)
using OMNITECH (S-AUTO) for the samples processed under varying current/time
situations was conducted with an indentation load of 50 gf and 10 s dwell time.
Results and Discussion
Microstructural Characterization of the Weld Zone
The characteristics and the role played by the multi-walled carbon nanotubes in the
nanocomposite formed in the weld nugget of the sample welded at 6500 A + 0.5 s are
depicted in Fig. 2a–c. Figure 2a portrays the clusters of carbon nanotubes embedded
in the iron matrix where a crack was also observed. This crack was formed due
to the electrode force used for welding. The carbon nanotubes tend to restrict the
propagation of such cracks in the matrix. Agglomerated carbon nanotubes were also
observed at some locations of the iron matrix. Carbon nanotubes were found to remain
embedded in the Fe matrix in both singly-dispersed and agglomerated forms which
T. Das
Characterisation Methods
For characterization purposes, the bare, graphene nanoplatelets-coated and multiwalled carbon nanotubes-coated samples of 19 × 5 × 1.85 mm were cut along the
weld nugget and normal to the specimen plane using Elektra Maxicut Wire Electric
Discharge Machine (EDM). The samples were then polished in sequence by various
emery paper grades and finally with a 0.25 and 1 μ grit diamond paste. Nital (97 ml
ethanol + 3 ml HNO 3 ) etchant was used for revealing the grains of steel and other
nanoparticles in the weld nugget. Scanning electron microscopy (SEM) and energy
dispersive spectroscopy (EDS) were done using EVO 18 Research ZEISS-SEM. The
study of strengthening mechanisms and IMCs was done using JEOL, JEM2100F field
emission gun-transmission electron microscope (FEG-TEM) functioning at 200 kV.
Mechanically thinned samples (70 μm thick) were used, and a hole was created at
the centre of the samples by precision ion miller (GATAN, model 691).
X-Ray (XRD) was performed using EMPYREAN PAN-alytical DY1705 X’PERT
PRO XRD with CuKα and a range of 20°–120°. The analysis was carried out on the
graphene nanoplatelets and multi-walled carbon nanotubes-coated interlayered fractured cross-sectional samples processed at the best welding current/time conditions.
The information obtained was evaluated using X-pert high-score software. Raman
spectroscopy was performed to investigate the stresses experienced by the nanoparticles (graphene nanoplatelets, multi-walled carbon nanotubes) on the processed
samples, and for this, JOBIN-YVON-HORIBA (T6400) equipped with Ar–Kr laser
(at wavelength λ = 514 nm) was used.
Lap shear experiments were conducted using servo-hydraulic operated INSTRON
(8800 MK3305) Universal Testing Machine with 1 mm/min crosshead speed and
ambient temperature for the welded samples under various current/time settings.
Fracture surface analysis was done at altered magnifications. Microhardness test (Hv)
using OMNITECH (S-AUTO) for the samples processed under varying current/time
situations was conducted with an indentation load of 50 gf and 10 s dwell time.
Results and Discussion
Microstructural Characterization of the Weld Zone
The characteristics and the role played by the multi-walled carbon nanotubes in the
nanocomposite formed in the weld nugget of the sample welded at 6500 A + 0.5 s are
depicted in Fig. 2a–c. Figure 2a portrays the clusters of carbon nanotubes embedded
in the iron matrix where a crack was also observed. This crack was formed due
to the electrode force used for welding. The carbon nanotubes tend to restrict the
propagation of such cracks in the matrix. Agglomerated carbon nanotubes were also
observed at some locations of the iron matrix. Carbon nanotubes were found to remain
embedded in the Fe matrix in both singly-dispersed and agglomerated forms which