Direct measurements of Rayleigh wave acoustoelastic constants for shot-peened superalloys

In this article, the experimental investigation of the dependency of surface wave (Rayleigh wave) acoustoelastic constants (AEC) on surface treatment parameters and plastic deformation is discussed. These constants are necessary for the monitoring of surface treatment intensity by means of ultrasonic testing. The indirect (mapping of bulk wave AEC to the surface wave AEC through the Grüneisen constants) method and the direct method are compared. Also the Rayleigh wave AEC have been directly measured for the different states of material (annealed, plastically deformed, or surface treated) for In718 and Ti6246 alloys. We show that surface AEC are very sensitive to any changes in material structure, up to changes in the sign of the effect, and for practical applications, the direct in-situ Rayleigh wave AEC measurement should be performed.