Ultrasonic Detection of Changes in the Elastic Properties of a 70−30 Iron-Nickel Alloy upon Heat Treatment

Ultrasonic attenuation and velocity measurements were made by the pulse-echo method on 30% nickel-70% iron alloy specimens after various steps in their transformation from austenite to martensite. It was found that the attenuation from Rayleigh scattering decreased, while that from elastic hysteresis increased as the transformation proceeded. It was concluded that the presence of the small martensite platelets in the grains reduced the anisotropy of the elastic constants of the grains, thus reducing the Rayleigh scattering. The increase in the hysteresis parallels the increase in residual strain and the increase in grain boundary material attending the transformation.