Effects of MXenes (Ti3C2Tx) deposition by drop casting on the fretting wear of structural concrete

In civil engineering, concrete is the most widely used material due to the availability of its components. Research on tribology of semi-rigid structural systems is important in civil engineering, as the initially rigid contact between concrete and metallic elements can generate micromovement, resulting in wear due to fretting and possible cracks. Recently, a new family of 2D metal carbide and nitride nanosheets called MXenes has stood out in tribological applications due to their layered structure, which provides self-lubricating and reinforcing properties, but they are costly and difficult to produce in large scale, making their use in civil engineering challenging, despite encouraging results from the literature. To overcome this, the present work proposed surface deposition of MXenes by drop-casting (involving very small amounts of Mxenes) to control fretting wear between concrete and steel. One and five applications were deposited from a dispersion at a concentration of approximately 0.4 mg/mL of MXenes in isopropanol. Fretting tests were carried out on concrete (with and without MXenes deposition) against steel counterbodies for a total stroke of 200 μm under different speeds (0.2 and 2 mm/s) and times (5 and 30 min). The results showed that the friction coefficients obtained in the fretting tests did not present a statistically significant difference when using Mxenes either as a reinforcement in the concrete or deposited by drop casting. The wear rates obtained from the fretting tests demonstrated that, for the lower speed, no significant difference could be confirmed for the modified concretes in either the 5 min or the 30 min tests. On the other hand, in the condition of speed = 2 mm/s and time = 5 min, the wear rate for one application of MXenes by dropcasting was lower than the reference. With a higher speed and 30-min test, a greater effect on the wear rate occurred, which may be the result of tribochemical effects in the contact. It is clear that, in this case, the MXenes nanosheets promoted agglomeration of the debris, partially transferring them to the counterbody; the formed tribolayer probably promoted the smoothing of the surfaces. This was confirmed by means of scanning electron microscopy (SEM) images and topographic parameters of the surfaces, which showed a smoother surface, especially with 1 application of MXenes. In energy dispersive X-ray (EDS) spectra, samples with 1 and 5 MXenes applications contained small amounts of titanium in the tracks, confirming that the MXenes nanosheets participated of the tribochemical reactions in the contact, contributing to the reduction of wear. These results demonstrate the potential of MXene deposition by drop casting, even in small quantities.