Non-destructive 3D characterization of microtextured regions in the bulk of Ti-6Al-4V alloy

Abstract

In this study we present spatially resolved texture and orientation maps from a cube-shaped sample of Ti-6Al-4V alloy, reconstructed by means of texture tomography (TT). Unlike grain resolved 3DXRD techniques which require "spotty" diffraction patterns, TT can reconstruct local (voxelized) orientation distribution function (ODFs) from continuous diffraction patterns collected in a 3D scanning procedure. Reconstructions of the same sample, scanned in two different settings and subsequent EBSD analysis parallel to one of the sample faces show excellent mutual agreement and validate the single-axis data collection and reconstruction procedure for this class of materials. The reconstruction reveals the presence and the 3D shape of several micro-textured regions, showing a sharp unimodal texture of the $α$-phase with a clear link of the orientation and spatial alignment of these zones to the rolling, transverse and normal directions of the rolled material.

Figures (4)

• Figure 1: ND IPF maps of a TD-ND plane close to the front surface of the sample cube. a,c) show the orientation of the $\alpha$-phase and b,d) show the orientation of the $\beta$-phase as found by a,b) EBSD and c,d TT respectively. As only a small fraction (2.7%) of the points were indexed as $\beta$ phase by EBSD, the indexed points are plotted as enlarged circles for easier visualization. e,f) shows the texture index computed from the TT reconstructions.
• Figure 2: Examples of measured scanning-diffraction data. a) Normalized scattering pattern from a single sample position after azimuthal regrouping. b) Normalized intensity summed over $hk\ell$-orders and azimuthal angle at a fixed sample height as a function of tomographic angle $\omega$ and scanning $y$-position. c,d) Normalized intensities of a single detector segment, both from the $0002$ diffraction ring at azimuthal angles marked in a). Experimental sample-averaged pole figures of the e) $\alpha$-phase $\{10\overline{1}0\}$ and f) $\beta$-phase $\{110\}$ reflection. The axis of the manual rotation is marked by $\mathbf{n}$ and the sense and magnitude is indicated by a red arrow.
• Figure 3: a) 3D rendering of the reconstructed cube colored by texture index. b) only regions of high texture index coloured by the inverse pole figure color of the mean orientation. c-e) $(0001)$ pole figures of c) regions with low texture index, d) regions with high texture index, and e) a single textured region. f-h) $(10\overline{1}0)$ pole figure of the same three textures as c-e).
• Figure 4: Stacked-histograms of voxel-by-voxel orientation error of two independent reconstructions after back-interpolation to a common coordinate system for the a) $\alpha$ and b) $\beta$ phases, respectively. c) Pearson correlation coefficient as a function of spatial resolution and d) as a function of angular resolution. Definition of correlation is provided in the supplementary information.