Detection of Micro-Voids by Evaluation for Attenuation Coefficient of Ultrasonic Waves Using Electromagnetic Acoustic Resonance Method on SUS 304 Fabricated by Hot Isostatic Press.

Abstract

It was evaluated creep damage by Electromagnetic Acoustic Resonance (EMAR), Noise Energy Method and Supersonic Spectroscopy (First Moment) Method on SUS 304 fabricated by Hot Isostatic Press (HIF) at 1050°C. Attenuation coefficient of electromagnetically excited acoustic wave in HIP has been investigated with frequency between 1.1 MHz and 5.4 MHz. Attenuation coefficient of the shear wave of as low as 2.5×10-4/μs at 1.1 MHz has been detected by reducing diffraction loss and the loss due to transmission of the ultrasonic wave to the electromagnetic acoustic transducer through the mechanical contact. The attenuation coefficient increases in proportion with frequency up to 5.4 MHz on the samples (specimen) fabricated with the pressure of 170 MPa. On the other hand, on the samples (specimen) fabricated with pressure lower than 80 MPa, the attenuation coefficient increases rapidly above 4 MHz. The void area fraction has been found to increase as the pressure decreases, which may be responsible for the rapid increment of the ultrasonic attenuation of the samples (specimen) fabricated with pressure lower than 80 MPa. As a result, it was clear that EMAR is more sensitive one to detect creep voids than the other methods. So We hope it is possible to use the actual facilitles in future.