Effect of ultrasonic amplitude on cavitation erosion characteristics of hydraulic turbine materials

Cavitation erosion would cause material loss and structural damage to the flow components of hydraulic turbines, which reduces their hydraulic efficiency and threatens the turbine's stable operation. Based on the ultrasonic cavitation test device, this paper investigates the effect of ultrasonic amplitude on the cavitation erosion of hydraulic turbine materials. The results show that the number and the volume of cavitation bubbles below the ultrasonic horn tip increased with the ultrasonic amplitude. The weight loss of S165, 1045, and S355 at ultrasonic amplitude 79 μm was 2.5, 1.67, and 1.84 times that at ultrasonic amplitude 52 μm, respectively. When the ultrasonic amplitude was 79 μm, the weight loss of S355 was 4.53 times that of S165. As the ultrasonic amplitude increased, the time for 1045 and S355 cavitation erosion to enter the maximum rate stage was shortened, while the S165 was still in the acceleration stage after 5 hours' test. The grain-boundary sliding and exfoliation of S165 were intensified, and the cavitation erosion pits in 1045 and S355 became larger and interconnected to form larger cavitation erosion pits with the ultrasonic amplitude. The number of cavitation erosion pits was more in S355 than in 1045, and the detachment of large-volume pearlite grains in 1045 and S355 at higher ultrasonic amplitude led to the large-volume cavitation erosion pits. The roughness of the three materials increased with the ultrasound amplitude. The roughness of 1045 and S355 was twice that of S165. The results were significant for the cavitation erosion protection of turbine materials.