Study on Phase Transformation Orientation Relationship of HCP-FCC during Rolling of High Purity Titanium

High purity titanium (Ti) thin strip was prepared by rolling with large deformation and was characterized by the means of Transmission Electron Microscopy (TEM), selected area diffraction (SAED) pattern, high-resolution (HRTEM) analysis, as well as Transmission Kikuchi Diffraction (TKD). It is found that there are face-centered cubic (FCC) Ti laths formed within the matrix of hexagonal close packing (HCP) Ti. This shows that the HCP-FCC phase transition occurred during the rolling, and a specific orientation relationship (OR) between HCP phase and FCC phase obeys ⟨0001⟩α// ⟨001⟩FCC and {100}α//{110}FCC. The ORs of HCP-FCC phase transition are deeply studied by TKD pole figure and phase transformation matrix. It is found that the derived results via pole figure and transformation matrix are equivalent, and are consistent with TEM-SAED analysis results, which proves that these two methods can effectively characterize the ORs of HCP-FCC phase transition and predict possible FCC phase variants.

Relation of quartz c-axis pole figures to deformation processes and flow

<p>Quartz c-axis pole figures are hugely popular for the estimation of various deformation conditions, such as strain state, slip system interpretation or deformation temperature. Most of these relations are purely empirical. Here we present quantitative results of the relation between microstructure and quartz c-axis pole figure data to add to the insights between deformation processes and texture development. We analyze EBSD data of experimentally sheared quartzite (kinematic vorticity number Wk = 0.9, experiments of Heilbronner & Tullis, 2006), a mylonitic quartzite from Eriboll (Wk = 0.5, Lloyd’s pers. collection) and a deformed quartz vein from the Tonale line (Wk = 0.4, Stipp & Kunze, 2008). All samples are composed of deformed old grains and recrystallized (by bulging and/or subgrain rotation) and deformed grains in variable proportions.</p><p>C-axis pole figures can be decomposed into several components (girdles and point maxima) which occupy distinct positions. These components can be related to two simple microstructural parameters, aspect ratio and long axis direction of grains. While the grain shape evolution in each of the samples differ in detail, they have several features in common:<br>1) c-axes of equiaxed grains occupy a position close to the inferred instantaneous shortening direction,<br>2) c-axes of grains with higher aspect ratios contribute to single girdle distributions,<br>3) the girdle position depends on the grain long axis direction,<br>4) grains with long axes parallel to the foliation (inferred XY plane of finite strain) provide highest c-axis concentrations in the center of the pole figure,<br>5) grains contributing to an oblique grain shaped foliation (“freshly” recrystallized, deformed grains) show elongated, peripheral maxima grading into single girdles inclined with the sense of shear and<br>6) grain shapes which relate to antithetic flow (in the low Wk samples), relations 3-5 hold, with the exception that the resulting peripheral maximum or girdle is also inclined against the sense of shear.</p><p>We interpret the individual c-axis pole figure components to reflect contributions from different processes which relate to oriented nucleation or growth (in the case of bulging recrystallization), as well as to a grains’ strain history. This strain history depends on the ratio of how fast a grain is straining (by glide) to how fast it is recrystallizing. The final c-axis pole figure of a polycrystalline aggregate simply reflects the weighted mixture of these components based on the synchronous contribution of each process.</p><p>The individual contribution of each process depends on several parameters (e.g., stress as a driving force for local grain boundary migration, grain boundary mobility, or rate of deformation among others). Since many of these parameters are also temperature-dependent, we suggest, for instance, that the variability of the c-axis opening angle with temperature is merely the result of the temperature different dependencies of the contributing processes. Hence, it is unsurprising that the so-called c-axis opening angle cannot be universally applied as a thermometer and is a good example of unrelated cause and correlation and may be expected to give arbitrary results.</p><p>References:</p><p>Heilbronner, R., Tullis J., 2006 https://doi.org/10.1029/2005JB004194, 2006.<br>Stipp, M. and Kunze, K., 2008  https://doi.org/10.1016/j.tecto.2007.11.041, 2008.</p>

Study of the texture of polycrystalline FCC materials using one incomplete direct pole figure

The article deals with the algorithm for texture analysis of polycrystalline materials using one direct pole figure (DPF). It is shown that the incomplete direct polar figure {111} for fcc materials contains the necessary information about the material texture. The algorithm provides identification of the preferred texture components in a multicomponent texture material and determination of their properties. The proposed algorithm is as follows. The upper hemisphere of the digital representation of the DPF is scanned by a polar complex of vectors that are normal to the reflection planes. Then the reliability parameters for each orientation are calculated and a set of the most reliable orientations is formed. The chosen orientations are recalculated to the Rodrigues space wherein the preferred texture components are formed by clustering. At the same time, an iterative algorithm with symmetry operators is used to avoid the umklapp effect. Each texture component is represented by the following parameters: Rodrigues mean vector, Miller indices, and Euler angles. The share and scattering of the texture component are also calculated. A method for selecting the optimal number of clusters providing presentation of the texture with the desired degree of detail is proposed. This is achieved by comparing two incomplete direct pole figures taken for {111} and {200} to select the maximum cluster scattering value on which the number of formed predominant texture components depend. The developed algorithm seems promising for rapid texture analysis, in analysis of sharp and weak textures and when there are less than three DPFs.

Multi-scale phase analyses of strain-induced martensite in austempered ductile iron (ADI) using neutron diffraction and transmission techniques

The content of strain-induced martensite in austempered ductile iron has been quantitatively determined using three different kinds of neutron methods: (1) high-resolution powder diffraction with subsequent standard Rietveld refinement, (2) phase quantification using pole figure measurements and (3) Bragg edge neutron transmission. The accuracy and scope of applications of these neutron diffraction and imaging techniques for phase quantification have been compared and discussed in detail. Combination of these methods has been confirmed as effective for dealing with problems like peak overlap in multi-phase materials and texture formation after plastic deformation. Further, the results highlight the potential of using single peak pole figure data for quantitative phase analysis with high accuracy.

Revealing the Subsurface Basal 〈a〉 Dislocation Activity in Magnesium Through Lattice Rotation Analysis

A method was proposed in this study to reveal the subsurface basal dislocation activity in Mg-Y alloy and determine the corresponding Burgers vector. This is achieved by correlating the slip directions of dislocations to the lattice rotation represented by the {0001} pole figure. The identified basal slip system by this approach was verified by micro-Laue diffraction. This method can be applied as a complementary method to the conventional slip trace analysis to study the dislocation behavior of Mg alloys.

Mechanism of Secondary Deformation of Extruded AZ31 Magnesium Alloy by Viscoplastic Self-Consistent Model

The viscoplastic self-consistent (VPSC) model is used to establish a combination of different deformation mechanisms. By using this model, axial tension and compression tests of extruded AZ31 magnesium alloy at room temperature are simulated. The influence of secondary deformation mechanism (prismatic <a> slip, pyramidal <c + a> slip, and 101¯1 compression twin) on mechanical response and texture evolution is expounded. Increased activity of the prismatic <a> slip is conducive for the improvement of flow stress in mechanical response during axial tension and for the splitting of pole densities in the {0002} pole figure during axial compression. However, increased activity of the pyramidal <c + a> slip causes the basal texture to transfer to the extrusion direction in the {0002} pole figure during axial compression. The 101¯1 compression twinning has a negligible influence on the plastic deformation and mechanical response of AZ31 magnesium alloy during axial tension and compression. However, the 101¯1 compression twinning should be included in VPSC modeling to predict the texture evolution accurately.

Elucidating the relationship between nanoparticle morphology, nuclear/magnetic texture and magnetic performance of sintered SrFe12O19 magnets

The relationship between nanoparticle morphology, self-induced atomic/magnetic texture and magnetic properties of high-performance hexaferrite magnets is elucidated using neutron/X-ray pole figure analysis and neutron/synchrotron powder diffraction.