Fretting Wear Properties of 904L Stainless Steel for Thermal Power in Different Atmospheres

The application of carbon dioxide to thermal power generation expected to develop a new type of high-efficiency thermal power generation system, which has the advantages of compact cycle system structure and high cycle efficiency. However, material failure caused by fretting wear has become one of the key problems restricting the development of its system. Therefore, it is of great significance to study the fretting wear properties of materials to ensure the stable operation of thermal power systems. In this study, the fretting wear test of 904L stainless steel heat transfer tube at different temperatures and environmental media (room temperature atmosphere, room temperature carbon dioxide, 350 ℃ atmosphere, 350 ℃ carbon dioxide) was carried out on the controllable atmosphere fretting wear test equipment. The displacement amplitude of the test was 60 μm, the normal load was maintained at 10 N, and 10⁵ test cycles were performed at a frequency of 10 Hz. Subsequently, the dynamic characteristics of the friction displacement curve and the friction coefficient curve were analyzed, and the wear scar morphology was observed and analyzed by a super-depth-of-field microscope. The wear scar three-dimensional morphology was characterized by an optical 3D surface profilometer. The cross-sectional profile, wear area and wear volume of the wear scar were measured. Scanning electron microscope and energy dispersive spectrometer were used to analyze the microscopic morphology and element composition of the surface and cross-section of the wear scar. The fretting wear mechanism of 904L stainless steel was further explored in different environments. The results showed that, the friction force displacement curve was an obvious parallelogram shape and the fretting wear running in the gross slip zone under room temperature conditions. The friction coefficient in the atmospheric environment was greater than that in the carbon dioxide environment. Significant material spalling and wear debris appeared in the fretting damage area, and accompanied by the initiation and propagation of cracks. The wear mechanisms of fretting wear under room temperature atmosphere and carbon dioxide environment were mainly delamination and oxidative wear. When the temperature raised to 350 °C, the friction force displacement curve changed from a parallelogram to an ellipse, and the fretting running in the mixed zone. Compared with the room temperature, the friction coefficient of fretting wear under 350 °C was reduced. However, the friction coefficient in the carbon dioxide environment was greater than that in the atmospheric environment. The wear debris generated by wear forms a “glaze layer” on the wear surface through the adhesion and sintering process, which inhibits the increase of wear. The highest oxygen content was detected on the wear surface in the atmospheric environment. The wear mechanisms in the atmospheric environment of 350℃ were mainly adhesive wear and oxidative wear. In the same carbon dioxide environment, a wear debris accumulation layer was formed on the surface of the wear scar, which inhibits the wear. However, due to the difference in tribochemistry, a compact “glaze layer” was not formed on the worn surface, and the wear debris tended to flow to the edge of the wear scar. Under the room temperature conditions, the wear amount of carbon dioxide was reduced compared with the atmospheric environment. When the temperature is increased to 350 °C, the wear amount was significantly smaller, and the wear amount in the carbon dioxide environment was slightly smaller than that in the atmospheric environment.