Impact Abrasive Wear of CoCrWSi Coating at High Temperature

With the development of steam turbines, the key parts of the steam turbine blades will suffer from mechanical damage, including friction wear and solid erosion, owing to the influence of high-temperature fluid and impurities. Therefore, materials used for the high-temperature components of steam turbines are required to have excellent thermal strength, oxidation resistance, and other comprehensive properties. Usually, high-temperature protective coatings are sprayed on these key components via various processes to improve the physical and chemical properties of the substrate at high temperatures. CoCrWSi coating is expected to become a protective coating for steam turbine parts owing to its excellent high-temperature oxidation resistance. However, there are few reports on the high temperature impact abrasive wear behavior of this coating. The CoCrWSi protective coating was prepared based on the steam turbine valve component material SA-182F92. The high temperature impact wear behavior of CoCrWSi coating in a sand erosion environment was studied by using self-developed high-temperature sand impact tester. The impact wear resistance of the coating was evaluated by dynamic response and impact wear scar morphology. The dynamic response data of the impact process, including the impact velocity curve and impact force curve, were obtained through the corresponding sensors. On the macro level, an optical microscope was used to observe the wear condition of the sample surface. On the micro level, SEM was used to observe the micro morphology of the surface and section of the wear scar, EDS was used to analyze the element distribution of the surface and section of the wear scar, and white light interferometer was used to measure the profile of the wear scar to obtain the maximum wear depth, area, and volume. The results show that the impact return velocity and impact force of the coating and substrate decrease with the increase in impact cycles, which is caused by the increase in contact area and decrease in stress during the impact. At the same impact cycles, the impact return velocity and impact force of the coating are greater than those of the substrate. The CoCrWSi coating has high-temperature impact abrasive wear resistance, which is specifically manifested in that under the same impact cycles. The wear area, wear volume, and wear scar depth of the coating samples are several times smaller than those of substrate samples, and the energy absorption and absorption rate of the coating samples are less than those of the substrate samples. In a high-temperature sand environment, a large number of sand particles will be embedded into the wear scar surface during the impact, and the irregular edges and corners of sand particles will aggravate this cutting effect. Then, a large number of grooves can be observed on the wear scar surface. In the high temperature sand environment, the wear mechanism of the substrate and coating is plastic deformation and abrasive wear. The difference is that the softened substrate has an obvious bulge at the edge of the impact area, resulting in serious plastic deformation. Although the coating did not completely peel off during the impact, micro cracks sprouted in the coating, and some coatings peeled off on the surface of the wear scar. The result was obtained under the condition of simulating the actual working condition of the steam turbine. The test parameters, such as heating temperature, sand material (impurities), and friction pair, were selected according to the actual working condition of the application background of the steam turbine coating, which has certain guiding significance for the application of CoCrWSi coating on steam turbine parts. © 2023 Chinese Mechanical Engineering Society. All rights reserved.