150
T. Das
C(222) are also observed at 2θ ~ 43.44° and 54.79°, respectively, which is because
of the presence of graphene nanoplatelets on the fractured interface. (110), (200),
(211), (220) and (310) Fe peaks are observed due to the presence of steel substrate
at 2θ ~ 44.66°, 65.5°, 82.49°, 99.35°, and 116.32°, respectively. Formation of an
intermetallic compound Fe 2 C (100) can be observed at 2θ ~ 37.4° whose formation
temperature (ε-Fe 2 C) is apsproximately 370–470 K [28]. It is also observed that the
intensities of the peaks go on decreasing with the decrease in welding current. Similarly, XRD spectra of the carbon nanotubes interlayered fractured specimens made at
the best welding parameters depict the formation of iron carbides and oxides (Fig. 3b).
Iron oxides mainly form because of the absence of any protective environment during
the processing. The XRD analysis displays three intense iron peaks at: (101) at 2θ
~ 43.53°, (110) at 2θ ~ 44.7°, (200) at 2θ ~ 64°, (211) at 2θ ~ 82.78°, (220) at 2θ ~
99.12° and (310) at 2θ ~ 115.28°. The sharpest peak of α-ferrite was obtained at 2θ
~ 44.77°. Another peak at 2θ ~ 99.12° also corresponds to α- ferrite. The formation
of iron carbide (Fe 2 C) was detected at 2θ ~ 37.6°, and FeC was detected at 2θ ~
110.5° mainly because of the solubility of carbon in Fe. These carbides are formed
mainly because of the lower formation temperatures of ε-Fe 2 C. A broadened peak
corresponding to elemental carbon peak, C(002) owing to the existence of carbon
nanotubes, was also detected at 2θ ~ 26°.
The bright-field image of the bare sample welded at an optimum current is
portrayed in Fig. 4a. The dislocations while sliding from one ferritic grain to the
other tend to get piled up at the grain boundaries. These piling up of dislocations at
the grain boundaries strengthens the nanocomposite by the grain boundary strengthening mechanism. The Fe-GNP interface where the interfacial shear stress transfer
takes place by mechanical interlocking has been shown in Fig. 4b. Figure 4c shows
the signature layered structure of the GNPs, whose geometry and structure help in the
strengthening of the nanocomposite formed at the weld nugget. The strengthening
mechanisms of the nanocomposite due to the incorporation of MWCNTs have been
depicted in Fig. 4d–f. Dislocation pileup and tangling of such dislocations around
the grain boundaries have been shown in Fig. 4d. Numerous precipitates were also
seen around the matrix owing to the rapid heating and cooling rates associated with
the RSW technique. Such precipitates act as obstacles to the dislocation movement.
Similar pileups have also been observed in Fig. 4e. Clusters of MWCNTs have been
shown in Fig. 4f which owing to their high aspect ratios helps in enhancing the
strength of the welded joint. Single-dispersed or clustered CNTs tend to orient themselves in a way to block the dislocation sliding which gets accumulated around the
grain boundaries and hence helps in work hardening and subsequent enhancement
in the strength of the nanocomposite formed at the weld nugget.
In Raman, graphene is typically categorized by two major D (~1350 cm
−1 ) and
G (~1580 cm
−1 ) bands as observed in Fig. 5a. This D-band is because of the lattice
distortion on the boundaries of the sp
2 group and the graphene lattice plane stretching
[29]. The G-band designates basic vibrational means of crystallite graphite, while
the D-band shows its disorderness. It also indicates the defects (sp
3 ) existing in the
formation. The 2D-band signifies the structure’s amount of layers. The existence
of these bands in different welding current/time setting designates the withholding
T. Das
C(222) are also observed at 2θ ~ 43.44° and 54.79°, respectively, which is because
of the presence of graphene nanoplatelets on the fractured interface. (110), (200),
(211), (220) and (310) Fe peaks are observed due to the presence of steel substrate
at 2θ ~ 44.66°, 65.5°, 82.49°, 99.35°, and 116.32°, respectively. Formation of an
intermetallic compound Fe 2 C (100) can be observed at 2θ ~ 37.4° whose formation
temperature (ε-Fe 2 C) is apsproximately 370–470 K [28]. It is also observed that the
intensities of the peaks go on decreasing with the decrease in welding current. Similarly, XRD spectra of the carbon nanotubes interlayered fractured specimens made at
the best welding parameters depict the formation of iron carbides and oxides (Fig. 3b).
Iron oxides mainly form because of the absence of any protective environment during
the processing. The XRD analysis displays three intense iron peaks at: (101) at 2θ
~ 43.53°, (110) at 2θ ~ 44.7°, (200) at 2θ ~ 64°, (211) at 2θ ~ 82.78°, (220) at 2θ ~
99.12° and (310) at 2θ ~ 115.28°. The sharpest peak of α-ferrite was obtained at 2θ
~ 44.77°. Another peak at 2θ ~ 99.12° also corresponds to α- ferrite. The formation
of iron carbide (Fe 2 C) was detected at 2θ ~ 37.6°, and FeC was detected at 2θ ~
110.5° mainly because of the solubility of carbon in Fe. These carbides are formed
mainly because of the lower formation temperatures of ε-Fe 2 C. A broadened peak
corresponding to elemental carbon peak, C(002) owing to the existence of carbon
nanotubes, was also detected at 2θ ~ 26°.
The bright-field image of the bare sample welded at an optimum current is
portrayed in Fig. 4a. The dislocations while sliding from one ferritic grain to the
other tend to get piled up at the grain boundaries. These piling up of dislocations at
the grain boundaries strengthens the nanocomposite by the grain boundary strengthening mechanism. The Fe-GNP interface where the interfacial shear stress transfer
takes place by mechanical interlocking has been shown in Fig. 4b. Figure 4c shows
the signature layered structure of the GNPs, whose geometry and structure help in the
strengthening of the nanocomposite formed at the weld nugget. The strengthening
mechanisms of the nanocomposite due to the incorporation of MWCNTs have been
depicted in Fig. 4d–f. Dislocation pileup and tangling of such dislocations around
the grain boundaries have been shown in Fig. 4d. Numerous precipitates were also
seen around the matrix owing to the rapid heating and cooling rates associated with
the RSW technique. Such precipitates act as obstacles to the dislocation movement.
Similar pileups have also been observed in Fig. 4e. Clusters of MWCNTs have been
shown in Fig. 4f which owing to their high aspect ratios helps in enhancing the
strength of the welded joint. Single-dispersed or clustered CNTs tend to orient themselves in a way to block the dislocation sliding which gets accumulated around the
grain boundaries and hence helps in work hardening and subsequent enhancement
in the strength of the nanocomposite formed at the weld nugget.
In Raman, graphene is typically categorized by two major D (~1350 cm
−1 ) and
G (~1580 cm
−1 ) bands as observed in Fig. 5a. This D-band is because of the lattice
distortion on the boundaries of the sp
2 group and the graphene lattice plane stretching
[29]. The G-band designates basic vibrational means of crystallite graphite, while
the D-band shows its disorderness. It also indicates the defects (sp
3 ) existing in the
formation. The 2D-band signifies the structure’s amount of layers. The existence
of these bands in different welding current/time setting designates the withholding