Introducing Compressive Residual Stress on Metal Surfaces by Irradiating Ultrasonic Wave with a Horn in Water : Surface Modification by Irradiating Ultrasonic Wave in Liquid (Report 1)

Ultrasonic wave of 19.5 kHz frequency oscillated with an ultrasonic transducer and amplified with a step type horn was irradiated on metal surfaces in water to introduce compressive residual stress. Slight plastic deformation occurred at the surface region of pure metal such as Cu and compressive residual stress was introduced. It seemed that the plastically deformed depth from the surface corresponded approximately to the region where the compressive residual stress is extended from the surface. The higher compressive residual stress could be introduced into the surface of Cu-Zn brass and SUS304 stainless steel because work-hardening was simultaneously induced to those alloys. Furthermore, since martensitic transformation was induced by the plastic deformation in the case of SUS304, the lager compressive residual stress could be introduced more deeply into the surface region. The residual stress of SUS304 surface reached to the maximum value of 574 MPa by irradiating for 5 min and the stress extended to the depth of about 170μm from the surface