arXiv subjects

Claire Griesbach

Publications and source records attributed to Claire Griesbach.

4 recordsLinked to original sources

arXiv2026

Global DIC-based sample-detector geometry refinement for accurate EBSD indexing

Electron backscatter diffraction is a powerful tool for mapping crystallographic microstructures. However, the primary crux to improving orientation accuracy and applying the technique to challenging materials lies in the correct calibration of the sample-detector geometry. Many approaches have aimed at overcoming this barrier through various pattern center calibration strategies, but the pattern center only defines part of the sample-detector geometry. Here, we present a DIC-based geometry refinement method that obtains a single map-consistent sample-detector geometry, refining both the pattern center and sample/detector angles. We effectively decouple the local orientation changes from the global geometry effects on the Kikuchi patterns by calculating the consistent map-wide simulated-to-experimental pattern shifts associated with global geometry parameter errors. Using single-crystal silicon and barium titanate (a material possessing six pseudosymmetric variants) as model materials, we demonstrate improved map-wide orientation consistency and more robust discrimination of pseudosymmetric variants than the Nelder-Mead and Differential Evolution optimization strategies.

cond-mat.mtrl-sci↗

arXiv2026

Ferroelectric polarization mapping through pseudosymmetry-sensitive EBSD reindexing

Ferroelectric materials exhibit a switchable, spontaneous polarization at the unit cell level--an attractive property utilized in many emerging technologies including, among others, high-density memory storage, low-power transistors, and high-speed fiber optic communication. Understanding the local polarization switching behavior, through domain nucleation and evolution, is critical to advancing these technologies and requires characterization of the local domain microstructure. However, in application-relevant polycrystalline materials exhibiting a distribution of grain orientations, a direct mapping of the polarization direction in three dimensions has remained inaccessible using conventional experimental approaches. Here, taking barium titanate single crystals and lead zirconium titanate polycrystals as our bulk model systems, we map the local polarization directions using a new electron backscatter diffraction indexing technique based on simulated pattern-matching. Through improved pre-processing techniques (including optimized pattern processing, a new pseudosymmetry-sensitive neighbor pattern averaging method, and DIC-based global sample-detector geometry calibration) and a new pseudosymmetry confidence index (which considers not only pattern similarity but pattern dissimilarity trends with other domain variant patterns), we successfully distinguish between the six polarization directions, despite the challengingly small unit cell aspect ratio of the selected materials. The methods developed in this work are not only applicable to ferroelectrics but any material which exhibits close crystallographic pseudosymmetries--extending the current capabilities of EBSD.

cond-mat.mtrl-sci↗

arXiv2023

Dynamic Hardness Evolution in Metals from Impact Induced Gradient Dislocation Density

A clear understanding of the dynamic behavior of metals is critical for developing superior structural materials as well as for improving material processing techniques such as cold spray and shot peening. Using a high velocity (from 120 m/s to 700 m/s; strain rates >10^7 1/s) micro-projectile impact testing and quasistatic (strain rates: 10^-2 1/s) nanoindentation, we investigate the strain-rate-dependent mechanical behavior of single-crystal aluminum substrates with (001), (011), and (111) crystal orientations. For all three crystal orientations, the dynamic hardness initially increases with increasing impact velocity and reaches a plateau regime at hardness 5 times higher than that of at quasistatic indentations. Based on coefficient of restitution and post mortem transmission Kikuchi diffraction analyses, we show that distinct plastic deformation mechanisms with a gradient dislocation density evolution govern the dynamic behavior. We also discover a distinct deformation regime-stable plastic regime-that emerge beyond the deeply plastic regime with unique strain rate insensitive microstructure evolution and dynamic hardness. Our work additionally demonstrates an effective approach to introduce strong spatial gradient in dislocation density in metals by high-velocity projectile impacts to enhance surface mechanical properties, as it can be employed in material processing techniques such as shot peening and surface mechanical attrition treatment.

cond-mat.mtrl-sci↗

arXiv2020

Origins of size effects in initially dislocation-free single-crystal metallic micro- and nanocubes

We report phenomenal yield strengths, up to one fourth of the theoretical strength of silver, recorded in microcompression testing of initially dislocation free silver micro and nanocubes synthesized from a multistep seed growth process. These high strengths and the massive strain bursts that occur upon yield are results of the initially dislocation free single crystal structure of the pristine samples that yield through spontaneous nucleation of dislocations. When the pristine samples are exposed to a focused ion beam to fabricate pillars and then compressed, the dramatic strain burst does not occur, and they yield at a quarter of the strength of their pristine counterparts. Regardless of the defect state of the samples prior to testing, a size effect is apparent, where the yield strength increases as the sample size decreases. Since dislocation starvation and the single arm source mechanisms cannot explain a size effect on yield strength in dislocation free samples, we investigate the dislocation nucleation mechanisms controlling the size effect through careful experimental observations and molecular statics simulations. We find that intrinsic or extrinsic symmetry breakers such as surface defects, edge roundness, external sample shape, or a high vacancy concentration can influence dislocation nucleation, and thus contribute to the size effect on yield strength in initially dislocation-free samples.

cond-mat.mtrl-sci↗