Pages 423-424
We studied microstructure evolution caused by creep in 2.25%Cr-1%Mo steel using ultrasonic attenuation. The material was exposed to the temperature of 923K at various stresses. We used electromagnetic acoustic resonance (EMAR) to measure attenuation. EMAR is a contactless acoustic-resonance method and is free from energy losses associated with contact transducer, resulting in the intrinsic attenuation solids. We use an axial-shear-wave EMAT, which transmits and receives SH wave propagating in the circumferential direction of a cylindrical specimen. The attenuation exhibits much larger sensitivity to the damage accumulation than the velocity. We explain the attenuation evolution with the microstructure change, especially, through the dislocation damping, which is supported by TEM observations. The technique has a potential to assess the damage advance and predict the creep life of metals
