Observation of bulk plasticity in a polycrystalline titanium alloy by diffraction contrast tomography and topotomography

The mechanical properties of polycrystalline metals are governed by the interaction of defects that are generated by deformation within the 3D microstructure. In materials that deform by slip, the plasticity is usually highly heterogeneous within the microstructure. Many experimental tools can be used to observe the results of slip events at the free surface of a sample; however, there are only a few methods for imaging these events in the bulk. In this article, the imaging of bulk slip events within the 3D microstructure is enabled by the combined use of X-ray diffraction contrast tomography and topotomography. Correlative measurements between high-resolution digital image correlation, X-ray diffraction contrast tomography, topotomography and electron backscattered diffraction are performed during deformation of Ti-7Al to investigate the sensitivity of the X-ray topotomography method for the observation of slip events in the bulk. High-resolution digital image correlation and electron backscattered diffraction measurements uniquely provide slip and lattice rotation activities at the surface of the specimen during deformation and are used to corroborate the diffraction contrast tomography and topotomography measurements. Much larger neighborhoods of grains were mapped by topotomography measurements than in previous studies, enabling quantitative measurements of slip transmission. Significant differences were observed between surface and bulk grains, indicating the need for 3D observations of plasticity to better understand deformation in polycrystalline materials.