Isolation and direct imaging of polycrystalline backscatter waves

The nondestructive quantification of grain feature information in polycrystalline aerospace materials is an important area of recent research, where information related to mean grain size, grain size distribution, and crystallographic orientation is needed for engineering analysis and remaining life predictions in aerospace engine components. In the present effort, the interaction of surface acoustic waves (SAW) with a dual-microstructure nickel polycrystalline material is studied, where the isolation and direct imaging of backscatter processes is made possible using time-gated wavefield imaging methods. The methods provide a means for studying the time-evolving nature of the backscatter energy fields, which suggest radially-expanding waves are generated by the individual and collective grain scattering events. This basic observation is consistent with longstanding backscatter theory considerations and is being used to understand the root-cause backscatter conditions that contribute to far-field ultrasonic signal capture.