Research On Cavitation Behavior And Strengthening Mechanism In Water-jet Cavitation Peening

Water-jet Cavitation Peening is a new type of metal surface strengthening treatment technology.Based on its own unique technical characteristics and advantages,it has attracted widespread attention in the field of metal surface modification since it is proposed.The basic principle is that the zoom nozzle can induce strong cavitation behavior in the submerged jet,and the cavitation frequently collapses on the surface of the target material to produce strong impact pressure,which causes elastic-plastic deformation of the near-surface material and induces a certain depth of residual compressive stress layer,thereby greatly improving the mechanical strength,wear resistance,fatigue resistance and corrosion resistance of metal parts.At present,most of the research on the Water-jet Cavitation Peening focuses on the optimization of process parameters,and the basic theoretical research related to cavitation in the process is still inadequate,which largely limits the further development and improvement of the technology.In this paper,the cavitation behavior and strengthening mechanism in the Water-jet Cavitation Peening were simulated and analyzed,and the strengthening effect in the process was explored through experiments.The main work content and conclusions are as follows:(1)Numerical simulation of the internal and external flow fields of the zoom-type cavitation nozzle by Fluent software shows that the existence of cavitation behavior can make the jet generate a higher jet velocity and a wider jet range.At the nozzle throat,the phenomenon of cavitation occurs due to strong pressure decline,and the cavitation behavior becomes more intense under the interaction of pressure difference of expansion angle and fluid shear.Adjusting the nozzle structure parameters(outlet opening angle,throat diameter)and incident pressure have higher influence to jet velocity and jet cavitation rate.,and the changing pattern is obtained.(2)The VOF multiphase flow model was used to simulate the collapse of a single cavitation on the surface of the target.The results show that: under different collapse distances,the morphological changes during the collapse of the cavitation bubble are different.When the cavitation collapse distance is different,the two mechanisms of "shock wave" and "microjet" can respectively strengthen the surface of the target material.It is calculated that the impact pressure generated by a single cavitation bubble is as high as 200?500MPa.(3)Using FUJI pressure measurement film,the impact pressure of the target material in the Water-jet Cavitation Peening was measured,and the peak impact pressure was higher than 300 MPa at the peening distance of 90 mm,and the pressure distribution pattern was obtained.Under the same experimental parameters,the surface strengthening of SAE1045 material before and after quenching was conducted by Water-jet Cavitation Peening method,and the measured residual compressive stress on the surface of the sample are 215 MPa and 535 MPa,and the depth of residual compressive stress layer reached 150?m.The reliability of the numerical simulation analysis of the Water-jet Cavitation Peening pressure and the effectiveness of the process for surface strengthening of the material were verified by the experiments above.