CORRELATION BETWEEN LOCAL ULTRASONIC PROPERTIES AND GRAIN SIZE WITHIN JET-ENGINE NICKEL ALLOY BILLETS

摘要

Ultrasonic velocity, attenuation, and back-scattered grain noise have been measured in rectangular coupons cut from representative 10"-diameter billets of IN718 and Waspaloy. Ultrasonic attenuation and backscattered noise were found to vary significantly with position within a billet, principally with radial depth. However, at a given measurement site there was little dependence of ultrasonic properties on inspection direction, suggesting an approximately equiaxed, untextured microstructure. Subsequent metallographic examinations revealed equiaxed grain structures in which the average grain diameter varied with position, tending to be largest at sites with large attenuations and large grain noise levels. The manner in which attenuation or backscattered-noise capacity (FOM) grows with increasing average grain diameter is similar to that expected for Pure-Ni microstructures. However, the rise rates are somewhat smaller for the jet-engine alloys, likely due to differences between the single-crystal elastic constants of the alloys and those of pure Ni. This paper reviews the methods used for ultrasonic measurements and metallographic analyses, and summarizes the interrelationships between attenuation, backscattered noise capacity and average grain diameter.