Luis Miguel Ballesteros Ospina¹, Daniel Toribio Gurrola¹, Jean Carlos - Zambrano Luna², Alexánder - Ruden Muñoz², Cesar Andrés Amaya Hoyos³, Juan Pablo - Trujillo Lemus², Jhonatan Eduardo Martinez³, Ines Carolina Ortega Portilla¹, Juan Manuel González Carmona^1
1Centro de Ingeniería y Desarrollo Industrial, Querétaro, México
²Universidad Tecnológica de Pereira, Pereira Colombia – La Julita
³Centro de Asistencia Técnica a la Industria ASTIN, Cali, Colombia
Current industrial needs require new coatings that reduce friction and wear under adverse conditions (e.g., high temperatures, vacuum, etc.). The use of solid lubricants has been employed to mitigate these conditions. Tungsten disulfide (WS₂) superlubricant coatings have become established as promising materials for friction reduction and improved wear resistance. Therefore, there is a demand to study the tribological properties of solid lubricants at high temperatures. This study presents a high-temperature tribological characterization of tungsten disulfide thin films deposited by magnetron sputtering. To study the evolution of the crystalline structure with respect to temperature, in situ X-ray diffraction analyses were performed from room temperature (RT) up to 700 °C. The results showed hexagonal phases of WS2, with some traces of trigonal phases, implying a loss of symmetry and crystalline disorder. As the temperature increased, stress relief was observed due to the shift of the peaks to higher diffraction angles, generating an increase in the lattice parameter. The diffraction patterns did not show significant changes until a temperature of 400°C. From this temperature, the presence of tungsten oxide (WO₃) peaks was observed on the surface due to the thermal and environmental conditions of the test. Increasing the temperature to 700°C revealed a decrease in the intensity of the WS2 phase and an increase in WO3, both in intensity and in the appearance of new peaks. Scanning electron microscopy of the surfaces after the 700°C test revealed the formation of globular and flower-like particles with sizes between 20 nm and 600 nm, along with the formation of porosity. To study the tribological behavior, tests were performed between room temperature and 600°C. At RT, a Coefficient of friction (COF) of 0.02 was reported, which remained constant for approximately 1200 cycles. Increasing the temperature to 250°C increased the COF to 0.1, which was sustained for approximately 2000 cycles. In both cases, after coating wear, the COF increased abruptly until reaching the substrate values. At a temperature of 600°C, due to oxide formation as observed by X-ray diffraction, the COF maintains low values only during the roughness removal stage. Subsequently, particle formation causes the COF to increase abruptly until reaching the substrate value. Scanning electron microscopy revealed delamination zones at the corners of the track due to predominantly abrasive wear mechanisms characterized by the generation of grooves, plowing, and micro-welding. Increasing the temperature to 250 °C resulted in no changes in the main wear mechanisms, except for the appearance of surface fatigue and increased abrasion. In both cases, the formation of a transfer film on the pin surface was observed. However, at 600°C, the formation of a large number of particles and extensive delamination of the coating were observed, and no transfer film was generated. The tribological effect of the films, as demonstrated by pin-disc tests, is evident at room temperature compared to uncoated D2 steel. A decrease in the coefficient of friction is observed due to the generation of a lubricating layer that reduces the COF. The lubricating behavior of the films is maintained at high temperatures; the appearance of oxides in the tribolayer is not as influential on the COF, since these are dynamically removed during sliding. The wear rates of the films showed a reduction in the material removed compared to the control surface. The wear traces show film degradation, debris accumulation, adhesion, and oxidation as the main mechanisms of coating wear. Traces of the film were also observed on the counterbody, confirmed by EDS analysis. The results confirm the implementation of thin films as an alternative for use as a solid lubricant in applications with complex and stable high-temperature environments.