Study of the relationship between ultrasonic properties and microstructure of nickel-based superalloy GH706

In this work, the effects of microstructure on the ultrasonic response of nickel-based superalloy GH706 (Inconel 706) were examined. The nickel-based superalloy was heat-treated under solution treatment, stabilising treatment and ageing treatment conditions. Metallographic tests were carried out and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images were taken to examine the microstructure of GH706. The ultrasonic and non-linear ultrasonic responses were detected and used for calculations. The results showed that changes in grain size directly affected the ultrasonic attenuation coefficient. In the cases where grain refinement was the main factor influencing the hardness of the specimens, changes in both longitudinal wave velocity and hardness were correlated to changes in grain size. However, it was found that if coherency strain is the main factor influencing hardness, the non-linear coefficient is sensitive to changes in both grain boundary structure and hardness, with greater incoherency at the grain boundaries correlating to a greater value for the non-linear coefficient. Finally, it was shown that changes in grain shape had only a minimal influence on the ultrasonic response.