Advances in near-field High Energy Diffraction Microscopy (nf-HEDM) with an Application to Recrystallization in AM 316L Stainless Steel

High-energy X-ray diffraction techniques can image 3-D microstructures of poly crystalline materials, bringing new insights into manufacturing and modeling. This thesis focuses on the technical aspects of High Energy Diffraction Microscopy (HEDM) development and a novel application to additive manufacturing (AM) materials. We first introduce the algorithm and implementation details of the GPU-accelerated third-generation HEDM reconstruction software HEXOMAP. The significant in crease in reconstruction speed is crucial in making HEDM more accessible to re searchers. In addition, new features allow easy adaptation to new experiment setups, expanding the application of HEDM. This thesis also describes the hardware de velopment of an in-situ furnace and its application in an annealing experiment on 3-D printed stainless steel sample. Four annealing cycles are measured with near field high-energy diffraction microscopy (nf-HEDM), far-field HEDM (ff-HEDM), and micro tomography (μ-CT) to capture microstructure evolution. Twin-related domains (TRDs) are identified by clustering grains contacting with 3 twin bound aries. The behavior of TRDs is analyzed, and several details of the recrystallization process of AM stainless steel are confirmed for the first time with in-situ 3-D mi crostructure mapping. The application of μ-CT on AM powders is also presented, which provides a quantitative analysis of the morphology and porosity of metal pow ders.