Precession electron diffraction assisted characterization of deformation in alpha and alpha + beta titanium alloys

Ultra-fine grained materials with sub-micrometer grain size exhibit superior mechanical properties when compared with conventional fine-grained material as well as coarse-grained materials. Severe plastic deformation (SPD) techniques have been shown to be an effective way to modify the microstructure in order to improve the mechanical properties of the material. Crystalline materials require dislocations to accommodate plastic strain gradients and maintain lattice continuity. The lattice curvature exists due to the net dislocation that left behind in material during deformation. The characterization of such defects is important to understand deformation accumulation and the resulting mechanical properties of such materials. However, traditional techniques are limited. For example, the spatial resolution of EBSD is insufficient to study materials processed via SPD, while high dislocation densities make interpretations difficult using conventional diffraction contrast techniques in the TEM.;A new technique, precession electron diffraction (PED) has gained recognition in the TEM community to solve the local crystallography, including both phase and orientation, of nanocrystalline structures under quasi-kinematical conditions. With the assistant of precession electron diffraction coupled ASTARAEE, the structure evolution of equal channel angular pressing processed commercial pure titanium is studied; this technique is also extended to two-phase titanium alloy (Ti-5553) to investigate the existence of anisotropic deformation behavior of the constituent alpha and beta phases.