Research on Hybrid Surface Modification by Cavitating Jet

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1. Injecting a cavitating jet to metallic materials such as stainless steel, silicon manganese steel, tool alloy and carbon steel, it was revealed that the cavitating jet can introduce compressive residual stress on the metallic materials by means of X-ray diffraction method. It was also revealed to evaluate the surface modification with depth from the surface by using Micro-Vickers hardness testing changing with the load.2. It was revealed that the corrosion resistance and the mechanical strength of carbon steel were improved at same time, i.e., hybrid surface modification, by using a cavitating jet.3. The flow rate of various type of nozzle was measured. The cylindrical nozzle was suitable for the cavitating jet for the hybrid surface modification in view point of repeatability.4. Cavitation impacts were measured by a PVDF transducer, which is developed by the investigators, for various cavitating conditions. The intensity of cavitation impact can be controlled by the upstream and downstream pressure of the nozzle.5. It was shown that the cavitating jet could improve the fatigue strength of aluminum alloy casting, silicon manganese steel and carbonized steel.6. Cavitating flow was affected by the shape of impinging surface. In order to treat gear, the optimum peening condition was investigated. It was revealed that the peened surface by a cavitating jet was very smooth comparing with that of the shot peening.7. It was shown that the roughness of the surface and the residual stress were main factor of optimum processing time. It will be possible to evaluate the surface modification by means of the residual stress using X-ray diffraction method.