Grain boundary character distribution derived from three-dimensional microstructure reconstruction

H Pirgazi,L A I Kestens

doi:10.1088/1757-899x/82/1/012086

Abstract

Manual serial sectioning which includes consecutive steps of sample preparation and Electron Back Scattering Diffraction (EBSD) measurement was employed to extract the twodimensional (2D) sections of a pure nickel sample and to reconstruct the three-dimensional (3D) microstructure. A general alignment algorithm based on the minimization of misorientation between two adjacent sections has been developed to accurately align the sections. By employing this alignment algorithm, any in-plane (translational) and rotational misalignment as well as the planparallelity can be corrected. Surface triangulation technique was used to reconstruct the grain boundary surfaces. The Grain Boundary Character Distribution (GBCD) was derived from reconstructed grain boundaries. The results show that a smoother grain boundary plane can be obtained after precise translational and rotational alignment and correction of planparallelity.The relative grain boundary energy was computed as a function of the five grain boundary parameters based on equilibrium at triple lines. The results show that the grain boundary planes carrying a Σ3 type misorientation are dominantly parallel to the {111} crystal plane, which indicates the presence of coherent twin boundaries. It was observed that coherent Σ3 type boundaries exhibit the minimum relative grain boundary energy, which is approximately 57% smaller than the average of all Σ3 boundaries, including also incoherent twin boundaries.

Highlights

Many microstructural features can be characterized with conventional 2D techniques, there remain many important microstructural properties that can only be measured in three-dimensions (3D). it is well-known that a full description of grain boundary planes is done with 5 parameters: 3 parameters of misorientation across the grain boundary and 2 parameters of the normal to the grain boundary plane [1]
The results show that the grain boundary planes of Σ3 type of misorientations are dominantly terminated by {111} crystal planes, which indicates the presence of coherent twin boundaries
A general alignment algorithm was used to correct in-plane and rotational misalignment as well as the planparallelity, which resulted in a better reconstruction of the 3D microstructure, illustrated by smoother grain boundary planes

Summary

Introduction

Many microstructural features can be characterized with conventional 2D techniques, there remain many important microstructural properties (e.g. detailed grain boundary features) that can only be measured in three-dimensions (3D). it is well-known that a full description of grain boundary planes is done with 5 parameters: 3 parameters of misorientation across the grain boundary and 2 parameters of the normal to the grain boundary plane [1]. Serial sectioning has been the most widely used method to acquire 3D data at the macro/microscale of opaque materials. In this technique, a series of closely spaced parallel sections reveal the third dimension of the microstructure. The usual method for serial sectioning involves the cyclic removal of parallel layers of the sample, followed by imaging (e.g. by EBSD) of the planar sections [4, 8]. The removal of the material for serial sectioning can be performed with different methods: e.g. mechanical polishing, chemical polishing, Focused Ion Beam (FIB) tomography and laser or electrical discharge ablation [5]

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