Performance of nanolubricants containing MoS2 nanotubes during form tapping of zinc-coated automotive components

Abstract

The paper presents the first use of nanolubricants containing MoS 2 nanotubes for form tapping of zinc-coated steel. MoS 2 nanotubes are known for their superb low frictional, anti-wear and extreme pressure properties and have shown a promising performance as nanolubricant additive in many machining and forming applications. However their interfacial interaction with zinc-coated components commonly used in automotive applications and their synergisms and antagonisms with currently used additives in forming oils are two crucial aspects that have not been addressed so far. The assessment of these synergies is of uttermost importance for developing future nanofluid minimum quantity lubrication formulations, since despite their extraordinary performance, MoS 2 nanotubes are not able to fulfil all the roles expected from a forming oil. To this end, this paper aims to investigate the performance of MoS 2-based nanolubricants in combination with representative forming oil additives. The threads are perform using a form tapping unit with customized data acquisition on zinc-coated steel, as a representative part in automotive applications. The performance of the nanolubricants is thoroughly investigated using advanced analytic methods with the aim of revealing the underlying interface interaction mechanisms for the observed torque behaviour and resulting thread morphology and sub-surface hardness. The results show that MoS 2 nanotubes are able to interact and form a tribofilm in Zn coated surfaces that leads to a superb friction performance. In combination with oil additives, MoS 2 based nanolubricants have a particularly positive synergy with extreme pressure additives in terms of friction reduction, sub-surface hardening and thread morphology. On contrary, the lowest synergy is achieved in the presence of dispersants, leading to higher torques during form tapping and higher sub-surface hardness in the formed threads.

Densification and tribofilm formation in hydrocarbon nanofluids induced by MoS2 nanotubes

“…The structure of liquid hydrocarbon is rearranged in the external solvation shell of the nanotube leading to ordered layers following the nanotube symmetry and extending well beyond those molecules in close contact with the surface which precludes building of an efficient extended tribolayer in dynamic conditions. This liquid hydrocarbon restructuring around the nanotube and the strong interaction between both systems can be considered as the building up of an effective antiwear coating, explaining antiwear MoS 2 properties [14,15,16]. In the case of confined molecules, they develop also patterns in the region around the nanotube centre as well as in the vicinity of the internal nanotube surface.…”

“…Thus, TMDs -nanoparticles [7,8], considering compounds such as MoS 2 [9] or WS 2 [10] have been largely tested under several tribological conditions and environments. TMDs nanoparticles as base oils additives have been considered in different forms, including fullerene-like [11], 2D monolayers [12,13] as well as nanotubes [14] and quantum dots [15].…”

“…Kalin et al [16] considered MoS 2 multiwalled nanotubes (MWNTs) and showed a 2-times reduction of friction and 5-9 times lower wear, showing a remarkable improvement with regard to the base oil based on the formation of MWNTs tribofilm on the surfaces. The superior performance of MoS 2 nanotubes and the formation of tribofilms have been considered for different material such as Zinc -coated surfaces [14], steel [17] or steel coated with materials such as TiN, TiAlN and CrN [18].…”

Recent Advances in Preparation and Testing Methods of Engine-Based Nanolubricants: A State-of-the-Art Review

“…Likewise, molybdenum sulphide (MoS 2 ) nano additives attract considerable attention, due to their distinctive wear properties, as mentioned in some studies [61,173]. It is believed that the friction-reduction capability of MoS 2 returns to its weak van der Waals primary atomic bonding that eases the slipping of MoS 2 layers and hence, forming the protective tribofilm [61].…”

The development of surface treatments on galvanised steel products for the automotive industry utilising a chemcoater

“…This interaction was important to understand to benefit the future development of nanofluid minimum quantity lubrication formulations. Results from the studies showed MoS2 interacted favourably with the Zn coating to form a tribological surface with superb frictional performance (114).…”