Model-Assisted Analysis of Local Attenuation in Ti-6Al-4V Materials

The nondestructive quantification of microstructure states in polycrystalline materials is an important area of recent research. Mean grain size estimates, for example, have been successfully made in a number of instances using frequency-dependent attenuation measurements and signal inversion theory based on statistically isotropic/equiaxed microstructure states and random crystallographic orientation conditions. In order to have a greater impact on engineering analysis and remaining life predictions, however, nondestructive evaluation estimates of local microstructure state variations are needed. In the present effort, forward ultrasonic models and targeted experiments are used to study and quantify the local statistical variability of microstructure states and ultrasonic signal response behaviors in synthetically generated and realistic Ti-6Al-4V titanium materials. An extension of equiaxed grain states to include extended log-normal grain size distributions is made, where local variations in the volumetric microstructure state, ultrasonic field scattering behavior, and frequency-dependent attenuation are evaluated using model-assisted studies and pulse-echo immersion ultrasound measurements.