Joseph A. Turner, Ph.D.
Michael P. Sealy, Ph.D.
Jeffrey E. Shield, Ph.D.
Date of this Version
Pratt, C. (2021). Ultrasonic Scattering Predictions from Polycrystalline Materials based on Electron Backscatter Diffraction Data. Master's Thesis, University of Nebraska-Lincoln.
Critical component failures in metallic parts are commonly caused by unintended microstructural defects or features. Although such failures are very rare, a critical failure in particular components may have the potential to cause human casualties or cost large sums of money. Microtextured regions within near-alpha titanium alloys are example features that are thought to play a key role in the failure mode known as titanium cold dwell fatigue. The detection and identification of microstructural features is well-established, though current techniques often require destruction of the component. In order to validate components with the potential for critical microstructural features, nondestructive detection and identification of those features is required. In this thesis, a method is presented by which microtextured regions can be detected and identified through nondestructive means. Microtextured regions are defined in this context as a collection of spatially localized alpha-Ti grains that share similar crystallographic orientations.
Every microstructure causes ultrasound to scatter due to the heterogeneous organization of the grains. The scattering pattern from microtextured regions with similar grain size distributions, grain morphologies, and crystal structure are dominated by changes in the crystallographic orientation distribution of the grains within the region. To determine if the characteristic scattering profiles of various microtextured regions could be differentiated from the scattering profile of the bulk microstructure, the crystallographic orientation information for each microtextured region was first extracted from electron backscatter diffraction data. Computer-based synthetic microstructures were created to be statistically equivalent to the real microstructures investigated, and ultrasonic scattering predictions were made using current mathematical models. The results showed dramatic differences between the scattering behavior of the bulk microstructure and that of the microtextured regions in the sample investigated. These results suggest that ultrasonic testing has the potential to detect microtextured regions. The thesis provides the basis for additional research into the specific ultrasonic signatures that result from microtextured regions such that enhanced inspection tools can be designed.
Adviser: Joseph A. Turner