Physics-aware global Rietveld refinement for high-energy X-ray diffraction microscopy with application to reconstructing intragranular orientation and strain fields

Abstract

High-energy X-ray diffraction microscopy (HEDM) has emerged as a critical technique for studying the microstructure and, increasingly, strain fields in solids. However, current algorithmic or experimental methods to obtain intragranular fields are time-intensive, provide limited spatial resolution, or yield stress and strain fields that do not satisfy the universal laws of deformation (compatibility and equilibrium). In the context of standard HEDM, a novel physics-aware approach is presented in which the physics of deformation is included in the forward diffraction simulation to ensure that the reconstructed fields are physically meaningful. The entire simulated and experimental diffractograms are compared with a differentiable optimal transport--type objective, and a Rietveld refinement is carried out globally on the internal fields and grain topology using gradient-based optimization. The method is developed, verified with synthetic data, and demonstrated experimentally using near-field HEDM data from aluminum oxynitride (a brittle ceramic), with a reference implementation released as PARA-X. The reconstructions show remarkable improvement over existing methods (improved completeness and loss), and the high-fidelity, high-resolution recovery paves the way for using HEDM to study fine-scale deformation mechanics over large polycrystalline volumes.