Effect of MoS2/Ti3C2Tx on Tribological Properties of Phosphate Coating at Elevated Temperature

As a typical environmental-friendly inorganic coating, the phosphate coating is widely used in aerospace, petroleum pipelines and marine equipment because of its strong adhesion, outstanding thermal stability and good corrosion resistance. In the present study, a phosphate bonding solid lubricant coating with excellent tribological properties at room temperature 25 (RT)-400 ℃ was prepared with MoS2/Ti3C2Tx as solid lubricant, and its friction reduction and anti-wear mechanisms at different temperature were investigated in detail. Ti3C2Tx MXene with "accordion" shape was prepared with hydrofluoric acid as etching agent from MAX phase (Ti3AlC2) powders. And then MoS2/Ti3C2Tx powders were prepared with thiourea, ammonium molybdate and MXene as raw materials. A Ti3C2Tx phosphate coating and A MoS2/Ti3C2Tx phosphate coating were prepared with Al(H2PO4)3 as binder and CuO as curing agent, and Ti3C2Tx and MoS2/Ti3C2Tx as solid lubricant filler respectively. The friction coefficients and wear rates of the coatings at 25-400 ℃ were investigated with a high-temperature friction and wear tester and an optical digital microscope. The surface morphology and phase of the wear scars were analyzed with a scanning electron microscope (SEM), a confocal laser Raman spectrometer and an X-ray diffractometer (XRD) respectively, and then the wear mechanisms at different temperature were discussed in detail. The main results were as follows. When the mass ratio of Ti3C2Tx to Al(H2PO4)3 was 2∶1, The friction coefficient and wear rate of the Ti3C2Tx phosphate coating were the lowest at RT, which were 0.38 and 2.75×10−4 mm3/Nm, respectively. As the temperature increased, the friction coefficient of the Ti3C2Tx phosphate coating increased from 0.38 at RT (25 ℃) to 0.79 at 400 °C, and the wear rate increased from 2.75×10−4 mm3/(N·m) to 7.34×10−4 mm3/(N·m). Compared with the Ti3C2Tx phosphate coating, the MoS2/Ti3C2Tx phosphate coating had significantly reduced coefficients at 25-400 ℃ and reduced wear rates. The MoS2/Ti3C2Tx phosphate coating showed a low friction coefficient of 0.11 at RT, which was 71.1% lower than that of the Ti3C2Tx phosphate coating. Moreover, the wear rate of the MoS2/Ti3C2Tx phosphate coating was 6.77×10−5 mm3/(N·m), which was an order of magnitude lower than that of the Ti3C2Tx phosphate coating. Continuous lubricating films with a small quantity of furrows could be observed on the sliding surface at RT, which showed that the main wear mechanism was abrasive wear. As the sliding temperature ranged from RT to 400 °C, the friction coefficient of the MoS2/Ti3C2Tx phosphate coating was kept below 0.21. With the increase of temperature, the friction coefficient of the MoS2/Ti3C2Tx phosphate coating showed a trend of decreasing firstly and then increasing, and the wear rate showed an overall increasing trend. The furrows on the wear scar gradually disappeared, and the formed lubricating films became smooth. From the Raman spectrum, mild oxidation could be found on the worn surface when the temperature was below 200 ℃, and the oxidation products were Ti3O5 and a small amount of MoO3. With the further increase of temperature, the oxidation degree of worn surfaces of the MoS2/Ti3C2Tx phosphate coating intensified. When the temperature was higher than 300 ℃, the oxidation products were TiO2 and MoO3. Owing to the synergistic lubrication of MoS2 and MoO3, the MoS2/Ti3C2Tx phosphate coating still has significant anti-friction property and improved wear resistance compared with the Ti3C2Tx phosphate coating at 400 ℃. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.