Strain mapping of individual grains using diffraction contrast tomography

This research project will aim to undertake a fundamental study of the early stages of plastic deformation in two types of polycrystalline alloys, low interstitial steel and commercially pure titanium (each material has a very distinct crystal structure, which has a strong impact on the deformation mechanisms), by using diffraction contrast tomography (DCT) on high-energy synchrotron x-ray radiation beam lines. Diffraction contrast tomography is a novel polycrystal grain and orientation mapping technique, which allows one to simultaneously characterize nondestructively and in 3D the grain shape and crystallographic orientation of a large number of grains in a polycrystalline material. This technique has been implemented at the European Synchrotron Radiation Facility (ESRF) beamline ID19 only very recently and substantial progress in terms of data analysis has led to the reconstruction of 1000 grains in aluminum and steel samples. To date, all diffraction contrast tomography work has been on fully recrystallised and undeformed material due to the limited contrast and diffused diffraction spots when working with material of high mosaicity. The aim of this project is to take DCT to the next level enabling the measurement the development of elastic strain between individual grains during the onset of plastic deformation. This elastic strain develops due to the crystallographic anisotropy of grains and can be used to study deformation mechanisms. Such measurements will be achieved by enhancements of the scanning procedures during DCT experiments and advances in the data analysis routine. The data recorded in this way will for the first time provide grain to grain strain/stress information, which can be used to develop and validate crystal plasticity finite element modeling.