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T. Das
the metals. Major limitations of resistance spot welding include low joint (nugget)
thickness and failure of the joints from the nugget itself. Moreover, highly thermally conductive metals like aluminium and magnesium require extensive surface
preparation and a high amperage current for welding. Also, the brittle intermetallic
compounds (IMCs) formation is detrimental for the joint strength which might lead
to brittle catastrophic fracture. Interfacial mode of failure weakens the weld joint,
and it is detrimental for the performance in the long run of the weld [1, 2]. AISI
1008 steel has exceptional weldability and aesthetics because of which this grade is
widely used in various industries. Also, because of the less amount of carbon present
in it, the development of carbides at the grain boundaries at the time of welding is
negligible.
In this background, present and early researchers have established numerous
techniques to increase the weld joint strength of similar/dissimilar metals and
also to curtail the brittle IMCs formation. These techniques include using doublepulsed current, pulsed current pattern, interlayers of varying thickness metals, and
thermos-compensated techniques [3, 4]. Interlayers of zinc [5–7], nickel [8], tin [9],
aluminium–silicon [10], graphene [11–13] and cold sprayed powders [14] were used
to weld similar and dissimilar metals like aluminium, steel, magnesium, copper and
their alloys. Such interlayers have been extensively used in resistance spot welding of
low carbon steel sheets (e.g. AISI 1008, AISI 1010 grades, etc.). Interlayers tend to act
as a barrier against the reaction between the welded metals and thus minimizing the
formation of intermetallic compounds. Significant improvement in fatigue behaviour
has also been reported due to the incorporation of these interlayers [15–17].
Graphene nanoplatelets (GNPs), possessing an elastic modulus of ~1 TPa and
tensile strength ~130 GPa, have been widely used both as a reinforcement [18] and
as a coating [19, 20] to enhance the bulk and surface properties of magnesium,
aluminium, steel, and polymers. The mechanical properties of graphene are dependent on the number of layers present and their associated defects. The existence of
graphene in aluminium–steel matrix helps in the strengthening of the composite by
various mechanisms including Orowan looping, grain refinement, pinning effect on
the grain boundaries, dislocation generation, and pile-up owing to the mismatch in
the thermal conductivities [11, 21]. Multi-walled carbon nanotubes (MWCNTs) are
well-acknowledged because of their outstanding thermal, mechanical, and electrical
properties which in combination with some suitable matrices improves the composite
strength. The combination of low density (~1.6 g/cm
3 ) along with the low coefficient of thermal expansion (CTE = 2 × 10
–5 K
−1 ) makes them the most attractive
reinforcement for enhancing the strength of the composite [22, 23]. Also, because
of their high aspect ratio (l/d ratio), they tend to buckle under compressive loads but
does not break and hence facilitate better matrix load transfer. Due to the possession of excessively high elastic modulus (~1 TPa) and tensile strength (~63 GPa),
carbon nanotubes do wonders in improving the composite strength by numerous
strengthening mechanisms [22].
The present study is mainly concerned with the integration of graphene
nanoplatelets and multi-walled carbon nanotubes as interlayers in the mating surfaces
of similar carbon steel (AISI-1008) steel joints. AISI-1008 steel has exceptional
T. Das
the metals. Major limitations of resistance spot welding include low joint (nugget)
thickness and failure of the joints from the nugget itself. Moreover, highly thermally conductive metals like aluminium and magnesium require extensive surface
preparation and a high amperage current for welding. Also, the brittle intermetallic
compounds (IMCs) formation is detrimental for the joint strength which might lead
to brittle catastrophic fracture. Interfacial mode of failure weakens the weld joint,
and it is detrimental for the performance in the long run of the weld [1, 2]. AISI
1008 steel has exceptional weldability and aesthetics because of which this grade is
widely used in various industries. Also, because of the less amount of carbon present
in it, the development of carbides at the grain boundaries at the time of welding is
negligible.
In this background, present and early researchers have established numerous
techniques to increase the weld joint strength of similar/dissimilar metals and
also to curtail the brittle IMCs formation. These techniques include using doublepulsed current, pulsed current pattern, interlayers of varying thickness metals, and
thermos-compensated techniques [3, 4]. Interlayers of zinc [5–7], nickel [8], tin [9],
aluminium–silicon [10], graphene [11–13] and cold sprayed powders [14] were used
to weld similar and dissimilar metals like aluminium, steel, magnesium, copper and
their alloys. Such interlayers have been extensively used in resistance spot welding of
low carbon steel sheets (e.g. AISI 1008, AISI 1010 grades, etc.). Interlayers tend to act
as a barrier against the reaction between the welded metals and thus minimizing the
formation of intermetallic compounds. Significant improvement in fatigue behaviour
has also been reported due to the incorporation of these interlayers [15–17].
Graphene nanoplatelets (GNPs), possessing an elastic modulus of ~1 TPa and
tensile strength ~130 GPa, have been widely used both as a reinforcement [18] and
as a coating [19, 20] to enhance the bulk and surface properties of magnesium,
aluminium, steel, and polymers. The mechanical properties of graphene are dependent on the number of layers present and their associated defects. The existence of
graphene in aluminium–steel matrix helps in the strengthening of the composite by
various mechanisms including Orowan looping, grain refinement, pinning effect on
the grain boundaries, dislocation generation, and pile-up owing to the mismatch in
the thermal conductivities [11, 21]. Multi-walled carbon nanotubes (MWCNTs) are
well-acknowledged because of their outstanding thermal, mechanical, and electrical
properties which in combination with some suitable matrices improves the composite
strength. The combination of low density (~1.6 g/cm
3 ) along with the low coefficient of thermal expansion (CTE = 2 × 10
–5 K
−1 ) makes them the most attractive
reinforcement for enhancing the strength of the composite [22, 23]. Also, because
of their high aspect ratio (l/d ratio), they tend to buckle under compressive loads but
does not break and hence facilitate better matrix load transfer. Due to the possession of excessively high elastic modulus (~1 TPa) and tensile strength (~63 GPa),
carbon nanotubes do wonders in improving the composite strength by numerous
strengthening mechanisms [22].
The present study is mainly concerned with the integration of graphene
nanoplatelets and multi-walled carbon nanotubes as interlayers in the mating surfaces
of similar carbon steel (AISI-1008) steel joints. AISI-1008 steel has exceptional