Ultrasonic Attenuation Peak during Creep of a Nickel-Base Superalloy with Electromagnetic Acoustic Resonance
Toshihiro OHTANI, Hirotsugu OGI and Masahiko HIRAO
Abstract:Electromagnetic acoustic resonance (EMAR) is a contactless resonant method with an electromagnetic acoustic transducer (EMAT). This method is free from extra energy losses, resulting in the measurement of intrinsic ultrasonic attenuation in solids. In this study, the EMAR was applied to detect the creep damage of a Ni-base superalloy (Waspaloy). The material was exposed to the temperature of 1073K at various stresses. We measured ultrasonic attenuation for 1-6-MHz frequency range as the creep advanced. The attenuation coefficient exhibits much larger sensitivity to the damage accumulation than the velocity. In a short interval, between 35% and 40% of whole life, attenuation experiences a large peak and ultrasonic velocity shows a small depression, being independent of the stress. This novel phenomenon is interpreted as resulting from microstructure changes, especially, dislocation mobility. This is supported by TEM observations for dislocation structure. This technique has a potential to assess the damage advance and to predict the creep life of metals. Key Words:Creep damage, Ni-base superalloy, EMAT, Ultrasonic attenuation, Non-contact evaluation, Dislocation