The Research Of Cavitation Erosion And Strengthening Of Pure Copper In The Water Cavitation Peening

Cavitation erosion phenomenon often appears on the surface of hydroturbines,ship propeller blades and some flow components.It causes plastic deformation and cavitation erosion damage on the surface of the material.Also decreases the intensity and fatigue performance of metal.It finally leads to a decline in efficiency,and even caused an accident.Artifacts of cavitation water peening technology are submerged in water and using high pressure water jet to produce cavitation effect to improve performance on the metal surface.In order to avoid cavitation damage and find the better cavitation water peening parameter,we should analysis the emergence and development of cavitation erosion phenomenon in cavitation water peening process.Water Cavitation Peening(WCP)was carried on the surface of pure copper with the different time and pressure.The surface cavitation damage and cross-sectional morphology of the test specimens were enhanced by WCP and analyzed by optical microscope,scanning electron microscope(SEM)and transmission electron microscopy(TEM).In combination with surface roughness,surface hardness and cross-section hardness determined which the best water cavitation peening strengthened process of pure copper.The results showed that there had some pits of plastic deformation and needle shaped cavitation erosion in the direct cavitating water jet damage zone in 5min under water cavitation peening pressure of 20MPa,the number of plastic deformation pit and needle shaped cavitation erosion increased after a period of peening time(15min-40min).Twin boundaries began to appear.The metal of surface spalled degree and the surface roughness increased obviously,and a large of deformation slip bands appeared.A large number of metal flaked off when water cavitation peening 90minutes.The damage rate of the mixed cavitating water jet damage zone was significantly lower than the direct cavitating water jet damage zone.Large and shallow cavitation pits which have observed grain morphology inside appeared in a short time.Along with time to grow the grain morphology of the whole region appeared,and also appeared more deformation slip bands at the grain inerior.But no metal flaked off.Cross-section of the direct cavitating water jet damage zone appeared a large number of up and down waves when the metal flaked off,and metal flaked along the grain boundary.The surface grain size bending deformation was along with the stress direction.The grains of cross-section has no obvious change at the mixed cavitating water jet damage zone,there were some dislocation cells at cross-section of two zones.Dislocation cells of the direct cavitating water jet damage zone were bigger than the mixed cavitating water jet damage zone.Under process of 20MPa pressure water cavitation shot peening,inside short time(5min),the direct cavitating water jet damage zone roughness rose sharply,the surface roughness within 30min to 60min process time leveling off,and maintained 2.9μm,it was less than the roughness of the machining requirements.The roughness of direct cavitating water jet damage zone increases rapidly when water cavitation shot peening 60min.Water Cavitation Peening improves surface hardness of pure copper obviously,surface hardness of the mixed cavitating water jet damage is greater than the direct cavitating water jet damage zone,and the depth of harden layer is greater than the direct cavitating water jet damage zone.Cross-section hardness results of different work pressure for water cavitation peening shows that the pressure greater and the hardening rate faster.In combination with hardness and surface roughness get the best water cavitation peening condition is 20MPa and 5Omin,the biggest hardness of the direct cavitating water jet damage zone is 110HV,maximum hardness of the mixed cavitating water jet damage is 95HV...