Effective structural unit analysis in hexagonal close-packed alloys - reconstruction of parent β microstructures and crystal orientation post-processing analysis.

Ruth Birch,Thomas Benjamin Britton

doi:10.1107/s1600576721011584

Abstract

Materials with an allotropic phase transformation can form microstructures where grains have orientation relationships determined by the transformation history. These microstructures influence the final material properties. In zirconium alloys, there is a solid-state body-centred cubic (b.c.c.) to hexagonal close-packed (h.c.p.) phase transformation, where the crystal orientations of the h.c.p. phase can be related to the parent b.c.c. structure via the Burgers orientation relationship (BOR). In the present work, a reconstruction code, developed for steels and which uses a Markov chain clustering algorithm to analyse electron backscatter diffraction maps, is adapted and applied to the h.c.p./b.c.c. BOR. This algorithm is released as open-source code (via github, as ParentBOR). The algorithm enables new post-processing of the original and reconstructed data sets to analyse the variants of the h.c.p. α phase that are present and understand shared crystal planes and shared lattice directions within each parent β grain; it is anticipated that this will assist in understanding the transformation-related deformation properties of the final microstructure. Finally, the ParentBOR code is compared with recently released reconstruction codes implemented in MTEX to reveal differences and similarities in how the microstructure is described.

Highlights

Burgers reported on the body-centred cubic to hexagonal close-packed orientation relationship (OR) in zirconium (Burgers, 1934) that had been previously reported by Vogel & Tonn (1931) using X-ray rotation photograph examination of very large zirconium crystals
For the parent microstructures, the initial reconstruction output [Fig. 6(3)] is based on the grain groupings identified using the Markov clustering (MCL) algorithm – the grain boundaries present are the non-Burgers orientation relationship’ (BOR) boundaries identified at step (ii)
The MTEX reconstruction algorithm does not include any of the post-processing analysis that we have described for the ParentBOR code

Summary

Introduction

Burgers reported on the body-centred cubic to hexagonal close-packed orientation relationship (OR) in zirconium (Burgers, 1934) that had been previously reported by Vogel & Tonn (1931) using X-ray rotation photograph examination (which would be called a variant of X-ray Laue diffraction) of very large zirconium crystals. This OR is known as the ‘Burgers orientation relationship’ (BOR). This transformation is important to understand the processing and performance of titanium, zirconium and hafnium alloys, which all have the allotropic phase diagram for high atomic fractions of the base metal in the alloy. Regions of common orientation appear due to the BOR and anisotropy within the strain path which leads to regions of (near) common orientation. Reports of these features vary in the literature, where they are broadly called ‘microtextured regions’ The only difference is that the loading conditions and safety considerations in their engineering applications will vary

Results

Discussion

Conclusion