Research Of Cavitation Erosion Behavior Of Copper Alloy And Design Of Test Device In Multi-phase Fluids

Ship propeller services in a complex multiphase flow system which includessolid, liquid and gas. Previous research has shown that erosion, cavitation and theinteraction of cavitation and erosion led to the failure of propeller. As one of mainfailure types for ship propeller, it is significant to study the cavitation damage rule andmechanism. In this study, we simulated the service environment of ship propeller andmeasured the cavitation behavior of tin brass. The main results are as follows:1. The failure behavior of tin brass, which is widely used in ship propeller, hasbeen investigated through rotating disk cavitation instrument. The results show that:(1) With increasing cavitation time, the cavitation process of tin brass showedfour stages, which were incubation period, rising, stabilization and attenuation stage.(2) The degree of cavitaion damage on the sample surface was closely related tothe location from the cavitation source. The closer the distance from the cavitationsource, the stronger the degree of cavitaion damage. With the increase of cavitationperiod, the surface roughness of the sample increased gradually. The area of cavitationpits became greater and greater, and their depth became deeper and deeper.(3) For the cavitaion damage of tin brass, microcracks first produced in theboundary between α and β phase in cavitation incubation period; in cavitation risingperiod, microcracks propagated along longitudinal direction; in cavitation stabilizationperiod, the longitudinal crack propagation and horizontal expansion of microcracksco-existed.(4) Hardening phenomenon was shown on the sample surface because ofcavitation, and the hardness first increased then decreased with the increase of thedepth. With increasing cavitation time, the thickness of hardening layer increased.(5) High dislocation density of the surface happenned because of cavitation,which effectively prevented crack extention and made the hardness increased, therebythe cavitation resistance of tin brass was enhanced.2．By analyzing the defects of existing equipment, we designed a set of cavitationand erosion instrument with electrochemical testing system. The machine can be usedto study cavitation, erosion and the interaction of cavitation and erosion in differentconditions, such as speed, sediment concentration, particle size of sand, temperature,pressure, and can also be used to measure dynamic electrochemical parameters.3. By use of the optimized instruments, the cavitation behavior of tin brass has been investigated in the water with and without sand. The results are as follows:(1) When the velocity of water was28m/s, the degree of cavitation damage wasstrongest, followed by31m/s and25m/s.(2) In water, the process of cavitation for tin brass can be divided into incubation,rising and stabilization period. In water containing sand, erosion and wear damage onthe sample surface happened because of the presence of sand, which shortened theincubation period, accelerated materials shedding, and enhanced the degree ofcavitation damage.