High energy white beam x-ray diffraction studies of strains in engineering materials and components
Keywords: residual stress
X-ray diffraction

The primary aim of this research was to develop and improve the experimental method and data interpretation for strain measurements using diffraction methods to gain a better understanding of micromechanical deformation and anisotropy of lattice strain response. Substantial part of the research was devoted to the development of the laboratory high energy X-ray diffractometer (HEXameter) for bulk residual strain evaluation.
White beam energy dispersive X-ray diffraction was chosen as the principal diffraction mode due to its extreme efficiency in utilising X-ray flux and its ability to capture large segments of diffraction patterns. The specimens that have been examined were real engineering components, mechanically deformed specimens and thermally treated specimens, ranging from dynamic in-situ measurements to ex-situ materials engineering. For the real engineering components, a wedge coupon from the trailing edge of a Ti64 wide fan blade and a turbine combustion casing were examined. Among the mechanically deformed specimens that have been measured were shot-peened steel plates, elasto-plastically bent bars of Mg alloy and cold expanded Al disks. Amongst the thermally deformed specimens, laser-formed steel plates, thermal spray coatings, a manual inert gas weld of Al plates, a friction stir weld of Al plates and Ni tubes and a quenched Ni superalloy cylinder used for strain tomography were studied. In-situ loading experiments have also been carried out, such as experiments on pointwise mapping of grain orientation and strain using the 3DXRD microscope at the ESRF and in-situ loading experiments on titanium alloy, rheo-diecast and high pressure diecast Mg alloy, IN718 Ni-base superalloy and Al2024 aluminium alloy. Experimental results from X-Ray diffraction and strain tomography were used to achieve a better understanding of the material properties. Some results were compared with polycrystal Finite Element model predictions
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Amongst the most prominent research achievements are the development on the HEXameter laboratory instrument, including: (i) the development of special collimation systems for the detectors and the source tube; (ii) the development of a twin-detector setup (that allows for simultaneous determination of strain in two mutually orthogonal directions); (iii) improved alignment procedures for better performance; and (iv) the adaptation of instrumentation for efficient scanning of both large and small components, that included choosing and adapting translation devices, programming of the translation system and designing sample mounting procedures.
In this research several approaches to data treatment were investigated. Quantitative phase analysis, single peak fitting (using custom Matlab routines and GSAS) and full pattern fitting (with individual pattern data refined by GSAS and batch refinement done by invoking GSAS via a Matlab routine) were applied. Different Matlab routines were written for specific experimental setups; and various analysis methods were selected and used for refinement depending on the requirements of the measurement results interpretation.
16 papers were published, ensuring that the results of this thesis are readily available to other researchers in the field.