Wear behavior of bare and coated 18Cr8Ni turbine steel exposed to sediment erosion: A comparative analysis

Abstract

Hydropower plant components are exposed to sediment erosion due to the impact of hard particles flowing along with the water. As a consequence, significant material loss and substantial reduction in efficiency are encountered during plant operation. This work investigates the sediment erosion problem in hydraulic turbines using a slurry erosion tester. Experiments are performed on bare and coated 18Cr8Ni turbine steel at three impact velocities i.e. 6, 8, and 12 m/s, and two impact angles 30° and 90°. The size of impacting particles varies between 50 to 350 µm with a slurry concentration of 2500 ppm. The erosion rate is found to be maximum at 30° impact angle and minimum at 90° impact angle. With an aim to minimize the erosion of turbine steel, the test samples were coated with in-house formulated ceramic-based coating material using the high-velocity oxygen-fuel thermal spray technique. Vickers hardness test was performed to determine the hardness of the coatings. For metallurgical characterization, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy techniques were used. A comparison of both bare and coated samples is carried out to observe the erosion-resistant aspects. A higher erosion resistance has been detected for the coated material as compared to the bare turbine material. The reduction in the erosion rate for coatings is 13.4% at 30° and 17.62% at 90° impingement angles. The obtained results are related to the tested materials’ microstructural, mechanical, and metallurgical aspects.