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This second part of the paper on an analysis strategy for data acquired using three-dimensional X-ray diffraction (3DXRD) describes the procedure for the determination of the grain characteristics for thousands of grains. The approach developed here is orders of magnitude faster than those presently available for indexing thousands of grains. Using information obtained from the steps described in Part I . J. Appl. Cryst. 45, 693-704], the volume, crystallographic orientation, centre-of-mass position and strain state of grains in the sample can be determined. The algorithms dealing with the determination of the orientation, centre-of-mass position and strain state of the grains are divided into two parts. The first deals with indexing, i.e. it assigns diffraction spots to individual grains assuming an unstrained lattice, and the second deals with the refinement of the crystallographic orientation, centreof-mass position and strain state of the grains using the diffraction spots assigned during indexing. The different approaches to indexing that exist in the literature are presented and compared with the novel approach developed here. Indexing can be run in two modes depending on the number of grains. For large numbers of grains, the approach employs a novel sample 'surface' scanning technique, in combination with a reduced number of search orientations, to achieve high robustness and computation efficiency. For small numbers of grains, the approach neglects the position of the diffracting grains in the sample in order to improve the computation efficiency. For unstrained samples, both modes of indexing and the subsequent process of refinement are validated using simulated data for 60 and 3000 grains. In both cases, the centre-of-mass position of the grains was determined with a mean error of 0.7 mm and the orientation was determined with a mean error of 0.0003 . Furthermore, an experiment was 'mimicked' by introducing experimental errors into the simulation for 3000 grains. The resulting mean errors in the centre-of-mass position (2.1 mm) and orientation (0.008 ) of the grains are higher than those for the ideal simulations, and the errors in an experiment will depend on the 'true' experimental errors. The algorithms dealing with strained samples are validated using a simulation for 3000 grains with mimicked experimental errors. The centre-of-mass position, crystallographic orientation, normal strain tensor components and shear strain tensor components of the grains were determined with mean errors of 8 mm, 0.006 , 5.2 Â 10 À5 and 2.8 Â 10 À5 , respectively. The possibility of obtaining grain-level information for thousands of grains with a high speed of acquisition makes the technique very attractive for in situ studies of thermomechanical processes in polycrystalline materials. research papers J. Appl. Cryst. (2012). 45, 705-718 Hemant Sharma et al. Grain characterization II 707

A fast methodology to determine the characteristics of thousands of grains using three-dimensional X-ray diffraction. I. Overlapping diffraction peaks and parameters of the experimental setup A data-analysis methodology is presented for the characterization of threedimensional microstructures of polycrystalline materials from data acquired using three-dimensional X-ray diffraction (3DXRD). The method is developed for 3DXRD microscopy using a far-field detector and yields information about the centre-of-mass position, crystallographic orientation, volume and strain state for thousands of grains. This first part deals with pre-processing of the diffraction data for input into the algorithms presented in the second part . J. Appl. Cryst. 45, 705-718] for determination of the grain characteristics. An algorithm is presented for accurate identification of overlapping diffraction peaks from X-ray diffraction images, which has been an issue limiting the accuracy of experiments of this type. The algorithm works in two stages, namely the identification of overlapping peaks using a seeded watershed algorithm, and then the fitting of the peaks with a pseudo-Voigt shape function to yield an accurate centre-of-mass position and integrated intensity for the peaks. Regions consisting of up to six overlapping peaks can be successfully fitted. Two simulations and an experiment are used to verify the results of the algorithms. An example of the processing of diffraction images acquired in a 3DXRD experiment with a sample consisting of more than 1600 grains is shown. Furthermore, a procedure for the determination of the parameters of the experimental setup (global parameters) without the need for a calibration sample is presented and validated using simulations. This is immensely beneficial for simplifying experiments and the subsequent data analysis. research papers J. Appl. Cryst. (2012). 45, 693-704 Hemant Sharma et al. Grain characterization I 695

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This work reports the procedure for selection of alloying elements to refine the microstructure of hardfacing Ni-Cr-B-Si-C alloys by providing in situ formed nucleation agents. It is concluded that the refining element should be able to spontaneously produce precipitates at high temperatures with little solubility in their Cr-rich counterparts. After exploring the theoretical backgrounds on how to select the refining element, Nb and Zr were selected and the phase formation reactions of Zr-or Nb-modified Ni-Cr-B-Si-C alloys were calculated using Thermo-Calc Ò simulations. Detailed microstructural analyses of the rapidly solidified samples deposited from the modified alloys showed that addition of Nb in specific quantities induces a significant microstructural refinement in the original Ni-Cr-B-Si-C alloy without deteriorating its high hardness. The Nb-modified alloy could be used to further investigate the viability of microstructural refinement as an effective toughening mechanism for Ni-Cr-B-Si-C and similar alloy systems.

Ultrasonic impact treatment (UIT) is a relatively novel technique applied to the toe of welded joints to improve the fatigue life by changing the weld geometry and the residual stress state. In this study, the stress relaxation due to ultrasonic impact treatment is investigated on a six pass welded high strength quenched and tempered steel section. Stress measurements in two orthogonal directions were conducted by energy dispersive synchrotron X-ray diffraction. Results show that the application of only ultrasound to a welded component re-distributes the residual stresses more uniformly, while mechanical impacts in combination with ultrasound is an effective way to release the residual stresses. After welding, diffraction peak broadening due to the lattice distortion, characterised by the full width at half maximum (FWHM), is observed in the region of the weld toes. Ultrasonic impact treatment reduces the FWHM at these locations.

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In multipass welding, each successive thermal cycle will introduce local melting, solid state phase transformations, grain growth, grain refinement, recrystallisation and recovery, all of which lead to a complicated stress state. Most stress measurements performed on multipass welded components represent the final residual stress state. Information concerning stress evolution on a pass-by-pass basis is difficult to find. In this investigation, six pass welds were made on high strength quenched and tempered steel sections, and depth resolved strain measurements in two orthogonal directions were carried out after each weld pass using energy dispersive synchrotron X-ray diffraction. The residual stresses were calculated using biaxial Hooke's law. A thermalmetallurgical-mechanical welding model was constructed and validated with temperature and pass-by-pass stress measurements, which improves the reliability of the model. Cross-sectional stress distributions are presented after each pass, revealing the weld stress development in multipass welds.