Study On Ultrasonic Cavitation Inhibition Methods For Underwater Alloy Materials

Cavitation is the main failure mode of flow components in hydraulic machinery such as turbines,pumps,and valves,which seriously affects the efficient operation and lifespan of these core components.It not only causes waste of energy and materials,but also brings economic losses.However,traditional underwater alloy materials are extremely susceptible to cavitation erosion and cannot meet the requirements for the use of these overcurrent components.Therefore,the properties of underwater alloy materials urgently need to be strengthened to improve their cavitation resistance.There are many devices that can cause cavitation erosion of underwater alloy materials.Ultrasonic cavitation equipment is more widely used in material cavitation research due to its simple operation and significant cavitation effects.In order to improve the cavitation resistance of underwater alloy materials,the following studies were conducted using ultrasonic vibration methods:The microgrooves with different widths were prepared on the surface of 6061 aluminum alloy using a laser marking device.Firstly,the hardness and roughness of the surface around the microgroove structure with different widths were measured.The results showed that there was no difference in the hardness and surface roughness of the aluminum alloy around the microgroove structure before the cavitation test compared to the smooth aluminum alloy surface.The morphology evolution process of microgrooves with different widths before and after the cavitation erosion test.It was found that when the widths were 0.05 mm and 0.1 mm,the microgrooves closed and did not have a good cavitation erosion resistance.However,the aluminum alloy material around the microgrooves with widths of 0.2 mm and 0.3 mm had excellent resistance to cavitation erosion.Subsequently,a microgroove structure with gradually changing width was prepared on the surface of 6061 aluminum alloy.The cavitation behavior of microgrooves with different widths has verified the influence of ultrasonic cavitation behavior on the surface of aluminum alloy to a certain extent.Through the above two test,0.3mm was the ideal width for the microgrooves.On the surface of 6061 alumimum alloy,a single microgroove with a width of 0.3 mm was created as part of microgrooves group structure,which improved the cavitation erosion resistance of the aluminum alloy.SLM316L stainless steel was subjected to ultrasonic shot peened.The phase composition,microstructure and microhardness of the samples were tested before and after ultrasonic shot peening.Then,ultrasonic cavitation erosion test was conducted.The results showed that ultrasonic shot peening did not change the phase composition of the sample.It was observed that the melt pool boundary of SLM316 L stainless steel disappeared in the shot peening deformation layer,and improved the interior microstructure to increase the microhardness of the sample.A comparative analysis was conducted on the surface morphology and threedimensional surface morphologies evolution of polished samples and ultrasonic shot peening samples before and after cavitation erosion test,explaining the mechanism of ultrasonic shot peening technology on ultrasonic cavitation erosion process.Due to the unevenness of the surface of the ultrasonic shot peening sample,it undergowent "grinding" under the action of ultrasonic cavitation erosion.The convex part of the specimen surface was the first to be impacted by cavitation bubbles due to its closer distance from the ultrasonic vibration head.The improvement of cavitation corrosion resistance of SLM316 L stainless steel by ultrasonic shot peening process was verified through microscopic morphology,three-dimensional morphology and surface roughness changes after ultrasonic shot peeing sample grinding.Two types of Stellite21 cladding layers were prepared on the surface of SLM316 L stainless steel using different scanning speeds during laser cladding.The phase composition,microstructure,and microhardness of the samples were tested at both scanning speeds,followed by ultrasonic cavitation tests.The different scanning speeds did not change the phase composition of the sample,which is composed of carbide phase and Co based phase.The sample with a scanning speed of 20 mm/s had higher microhardness due to its fine microstructure.When the scanning speed is 30 mm/s,large cracks appeared on the surface of the sample.Therefore,the ultrasonic cavitation behavior in both the cracked and non-cracked areas of the sample was observed.It was found that the presence of cracks led to more severe cavitation damage.The changes in surface morphology,three-dimensional topography,and roughness of the sample before and after cavitation erosion were compared between the surface without cracks at a scanning speed of 30 mm/s and the sample at a scanning speed of 20 mm/s.It was found that the coarseness of Co base phase in the crack free eara at the scanning speed of 30 mm/s led to weaker cavitation erosion resistance than the sample at scanning speed of 20mm/s.According to the test result,the cavitation erosion resistence of the sample with a scanning speed of 20 mm/s was also better than that of the ultrasonic shot peening sample.