Tests of Microstructure Reconstruction by Forward Modeling of Hedm Data

Verification tests of the forward modeling technique for near-field high energy diffraction microscopy (HEDM) are conducted using two simulated microstructures containing uniformly distributed orientations. Comparison between the simulated and reconstructed microstructures is examined with consideration to both crystallographic orientation and spatial geometric accuracy. To couple the simulations with the evolving experimental setup at the Advanced Photon Source 1-ID beamline, simulated data sets use two different detector configurations; all parameters mimic the experimental geometry. Results indicate that element orientations are distinguishable to less than 0.1 degrees, while spatial geometric accuracy is limited by detector resolution. INTRODUCTION Large three dimensional maps of microstructures based on orientation imaging microscopy (OIM) (Adams et al., 1993; Wright and Adams, 1992), have become available in the last few years due to the availability of automated serial sectioning and dual focused ion beam electron microscopes. (Uchic et al., 2006, Lee et al., 2007) The drawback to these measurements is that they, of necessity, destroy the measured material as sectioning proceeds. High energy x-ray diffraction microscopy (HEDM) (Poulsen, 2004; Suter et al., 2008; Lienert et al., 2007; Suter et al., 2006) is one of several new x-ray techniques (Ludwig et al. ,2008; Larson et al., 2002) that permit spatially resolved non-destructive measurement of volumes of polycrystal microstructures. These techniques allow the monitoring of responses of ensembles of grains as various thermo-mechanical stimuli are applied and thus open the way to constraining theoretical models of microstructure response. Third generation synchrotron based HEDM is able to map three dimensional, macroscopic volumes of microstructures at micron scale resolution with better than 0.1 degree orientation resolution. This paper characterizes minimum uncertainties and noise levels in reconstructed microstructure maps. Simulated diffraction data sets are generated from artificial (and thus, known) microstructures. The analysis software then uses these data sets to attempt to reconstruct the initial microstructure. By comparing initial and reconstructed structures, we obtain several quantitative measures of precision and accuracy in terms of both crystallographic orientation and real space geometry. Two synthetic microstructures, one with a small number of large grains and 141 Copyright ©-International Centre for Diffraction Data 2010 ISSN 1097-0002