In situ laser-based resonant ultrasound measurements of microstructure mediated mechanical property evolution

In situ laser-based resonant ultrasound spectroscopy is used to characterize the development of a recrystallized microstructure in a high purity copper sample. The modal shapes, used for mode identification, of several resonant modes are determined before and after annealing by raster scanning the laser interferometric probe. This information is used to isolate the motion of individual modes during high temperature annealing. The evolution of a particular mode during annealing is examined in detail. During recrystallization, the center frequency of this mode shifts by approximately 20% of the original value. Using electron backscatter data it is shown that the majority of this shift is due to changes in the polycrystal average elastic stiffness tensor, driven by changes in texture, and that changes in dislocation density and pinning length are secondary influences.