A method for crystallographic mapping of an alpha-beta titanium alloy with nanometre resolution using scanning precession electron diffraction and open-source software libraries

Abstract

An approach for the crystallographic mapping of two-phase alloys on the nanoscale using a combination of scanned precession electron diffraction and open-source python libraries is introduced in this paper. This method is demonstrated using the example of a two-phase alpha / beta titanium alloy. The data was recorded using a direct electron detector to collect the patterns, and recently developed algorithms to perform automated indexing and analyse the crystallography from the results. Very high-quality mapping is achieved at a 3nm step size. The results show the expected Burgers orientation relationships between the alpha laths and beta matrix, as well as the expected misorientations between alpha laths. A minor issue was found that one area was affected by 180{\deg} ambiguities in indexing occur due to this area being aligned too close to a zone axis of the alpha with 2-fold projection symmetry (not present in 3D) in the Zero Order Laue Zone, and this should be avoided in data acquisition in the future. Nevertheless, this study demonstrates a good workflow for the analysis of nanocrystalline two- or multi-phase materials, which will be of widespread use in analysing two-phase titanium and other systems and how they evolve as a function of thermomechanical treatments.