Study On Anti-cavitation Property Of Cast Iron Material Based On The Improvement Of Laser-induced Cavitation Strengthening

Cavitation is a common phenomenon in hydraulic equipment,which can cause the damage problem to the hydraulic machinery and other components on safety performance.In this paper,cast iron usually used in the pump is chose as the research material.The high speed micro-jets and the impact pressure caused by laser-induced cavitation bubble collapsing are simulated by fluid-solid coupling method in ANSYS software.The impacts of cavitation on the deformation and stress distribution of cast iron material are analyzed with different laser parameters.The experiment platform of cavitation research is built to investigate the effects between cavitation phenomenon and the property of cast iron samples.In order to make visual study on cavitation erosion behavior of the material in different cavitation erosion time,the ultrasonic cavitation erosion experiment platform is also prepared.The main research contents and results are listed as follows:(1)The VOF multiphase flow model,laser thermal effect formula and other simulation variables are combined together in ANSYS simulation software to discuss the high speed micro-jets and the impact pressure caused by cavitation bubble collapsing near the solid boundary.It can be found that with the increase of the defocusing amount H,the velocity of micro-jet accompanied with the impact pressure increase firstly,then decrease sharply,and reach the maximum value when the defocus amount is 1mm.The results of high-speed micro-jet in the fluid domain are introduced into the solid domain simulation to analyze the influence on the deformation and stress distribution under different laser parameters.The results show that the distribution of residual compressive stress in cast iron is hemispherical,and the maximum residual compressive stress in the sample appears in the subsurface stratum of the impact area.(2)The experiment method of laser-induced cavitation is used to discuss the three-dimensional morphology and residual stress distribution of cast iron surface under different laser energy and defocus parameters.The results show that with the increase of laser energy,the maximum depth and the residual compressive stress value of the impact area also increase.The residual compressive stress of the impact area increases firstly and then decreases,which will reach the peak value at the condition of H=1mm.The three stages of the mechanism from laser-induced cavitation to the cast iron samples are summarized,and the experimental conclusions are compared with simulation results to verify its validity and the feasibility of fluid-solid coupling method.(c)The cavitation erosion mechanism of cast iron matrix on crack initiation,crack growth,plastic deformation accumulation and material desquamation are discussed detailedly in the different corresponding cavitation erosion stage.The changing reasons of morphology and hardness in different cavitation erosion time are investigated to show the anti-cavitation properties of cast iron and the cavitation erosion mechanism of laser-induced cavitation impact area on deformation fracture under different laser parameters.It can be found that with the increase of laser energy,the increase of hardness on impact area is also obvious.When the surface of cast iron is damaged by cavitation erosion,the plastic deformation and work-hardening phenomenon will occur at the surface.At the same time,the hardness will increase firstly and then decrease.However,with the increase of the defocus amount H,the reduction and reduction rate of the impact area show the variation trend of first decrease and then increase,which will reach the minimum value at the condition of H=1mm.