P.S. Bate

Bio: P.S. Bate is an academic researcher from University of Manchester. The author has contributed to research in topics: Grain boundary & Grain growth. The author has an hindex of 17, co-authored 21 publications receiving 1276 citations.

Crystallographic variant selection in Ti–6Al–4V

Abstract: Transformation textures in the two-phase alloy Ti–6Al–4V have been studied Samples were heated into the fully β phase condition and then slow cooled to allow diffusional transformation to α This produced a microstructure of grain boundary α encircling colonies of Widmanstatten α Electron backscattered diffraction (EBSD) texture measurements showed that the α texture was markedly sharper than that calculated on a basis of equal variant probability, indicating that significant variant selection was occurring during diffusional transformation Investigation of the α variants produced across prior β grain boundaries has shown that the selection of variants during transformation is highly dependant on the crystallography of those boundaries The effect of this crystallographic variant selection on the transformation texture has been modelled

Orientation averaging of electron backscattered diffraction data

Abstract: The use of data averaging to improve the angular precision of electron backscattered diffraction (EBSD) maps is discussed. It is shown that orientations may be conveniently and rapidly averaged using the four Euler-symmetric parameters which are coefficients of a quaternion representation. The processing of EBSD data requires the use of an edge preserving filter and a modified Kuwahara filter has been successfully implemented and tested. Three passes of such a filter have been shown to reduce orientation noise by a factor of approximately 10. Application of the method to deformed and recovered aluminium alloys has shown that such data processing enables small subgrain misorientation (< 0.5 degrees ) to be detected reliably.

Modelling texture development during equal channel angular extrusion of aluminium

Abstract: The deformation textures that develop in aluminium during ECAE (without rotation of the billet) have been investigated experimentally and modelled using the FC-Taylor approach, for two different die angles (90 and 120°), by using actual deformation histories measured from scribed marker grids. This has shown that the deformation during ECAE can best be described in terms of streamline coordinates and involves a simple shear parallel to the streamline, which becomes aligned with the final extrusion direction, and a plane strain tension and compression component that develops as the material enters and leaves the dies deformation zone. The textures observed were similar to those found following torsion straining and had the main components {001}〈110〉 and {112}〈110〉 along a B partial fibre. However, in the case of ECAE, the positions of maximum intensity were rotated by ~15–20° about the transverse direction (TD). Similar textures were seen for even and odd numbers of extrusion passes, suggesting that the TD rotation is not caused by alignment of the fibre direction with the die’s ‘shear plane’, as has been previously reported. In contrast, texture simulations showed that this rotation occurs as a consequence of the additional plane strain compression component in ECAE deformation.

Deformation mechanisms and plastic anisotropy in magnesium alloy AZ31

Abstract: The magnesium alloy AZ31 shows a significant drop in the normal anisotropy between room temperature and ∼200 °C. It has been suggested in the literature that this drop could be the result of grain boundary sliding (GBS). This paper further examines the notion of GBS at these temperatures through observation of surface relief, grain boundary shearing, and quantification of intergranular and intragranular strain distributions. It was found that there is negligible grain boundary sliding at any test temperature. The only significant change in deformation behaviour between 25 and 150 °C is an increase in the homogeneity of slip at the higher test temperature. It is concluded that the drop in normal anisotropy with increased test temperature is unlikely to result from GBS, and more likely to be the result of an increase in pyramidal slip activity at higher test temperatures.

Diffusion creep and superplasticity in aluminium alloys

Abstract: The plastic deformation of two classes of fine-grained aluminium alloys at elevated temperatures and slow strain rates have been investigated One class of material, Al–Cu–Zr, was processed to develop banded microstructures; the other class, based on Al–(Mg)–Mn, had near-equiaxed microstructures In both classes, superplastic behaviour was found in the variants with the higher solute content The evolution of the banded microstructures and the results from surface grid measurement in the Al–(Mg)–Mn alloys give results which indicate that the superplasticity is primarily a result of diffusion creep, and the effect of solute is proposed to be via an enhancement of solvent self-diffusion

Large-scale 3D random polycrystals for the finite element method: Generation, meshing and remeshing

Abstract: A methodology is presented for the generation and meshing of large-scale three-dimensional random polycrystals. Voronoi tessellations are used and are shown to include morphological properties that make them particularly challenging to mesh with high element quality. Original approaches are presented to solve these problems: (i) “geometry regularization”, which consists in removing the geometrical details of the polycrystal morphology, (ii) “multimeshing” which consists in using simultaneously several meshing algorithms to optimize mesh quality, and (iii) remeshing, by which a new mesh is constructed over a deformed mesh and the state variables are transported, for large strain applications. Detailed statistical analyses are conducted on the polycrystal morphology and mesh quality. The results are mainly illustrated by the high-quality meshing of polycrystals with large number of grains (up to 10 5 ), and the finite element method simulation of a plane strain compression of e = 1.4 of a 3000-grain polycrystal. The presented algorithms are implemented and distributed in a free (open-source) software package: Neper.

Effect of build geometry on the β-grain structure and texture in additive manufacture of Ti6Al4V by selective electron beam melting

Abstract: With titanium alloys, the solidification conditions in Additive Manufacturing (AM) frequently lead to coarse columnar ?-grain structures. The effect of geometry on the variability in the grain structure and texture, seen in Tisingle bond6Alsingle bond4V alloy components produced by Selective Electron Beam Melting (SEBM), has been investigated. Reconstruction of the primary ?-phase, from ?-phase EBSD data, has confirmed that in bulk sections where in-fill ?hatching? is employed growth selection favours columnar grains aligned with an ? direction normal to the deposited powder layers; this results in a coarse ?-grain structure with a strong ? fibre texture (up 8 x random) that can oscillate between a near random distribution around the fibre axis and cube reinforcement with build height. It is proposed that this behaviour is related to the highly elongated melt pool and the raster directions alternating between two orthogonal directions every layer, which on average favours grains with cube alignment. In contrast, the outline, or ?contour?, pass produces a distinctly different grain structure and texture resulting in a skin layer on wall surfaces, where nucleation occurs off the surrounding powder and growth follows the curved surface of the melt pool. This structure becomes increasingly important in thin sections. Local heterogeneities have also been found within different section transitions, resulting from the growth of skin grain structures into thicker sections. Texture simulations have shown that the far weaker ?-texture (~ 3 x random), seen in the final product, arises from transformation on cooling occurring with a near random distribution of ?-plates across the 12 variants possible from the Burgers relationship.

Grain structure formation during friction stir welding observed by the ‘stop action technique’

Abstract: Experiments have been carried out to ‘freeze’ the friction stir welding process by stopping the tool and immediately quenching the work piece in an Al-2195 plate welded under typical conditions. Sectioning through the ‘frozen’ weld keyhole with the tool in place has allowed the microstructure development, leading to the formation of the ultrafine grained nugget material, to be directly observed as fresh material encounters the deformation field surrounding the rotating pin. The grain refinement process is shown to be driven by grain subdivision at the colder periphery of the tools deformation zone, and the geometric effects of strain, which together reduce the overall high angle boundary spacing with increasing deformation. However, it also involves thermally activated high angle grain boundary migration, which increases as the temperature rises towards the tool. The higher temperature latter stages of the refinement process are closely reminiscent of geometric dynamic recrystallisation seen in high strain hot torsion experiments. The nugget grain structure has also been found to become more equiaxed and coarsens slightly, due to static annealing in the thermal wake of the tool.

Texture evolution in equal-channel angular extrusion

Abstract: The focus of this article is texture development in metals of fcc, bcc, and hcp crystal structure processed by a severe plastic deformation (SPD) technique called equal-channel angular extrusion (ECAE) or equal-channel angular pressing (ECAP). The ECAE process involves very large plastic strains and is well known for its ability to refine the grain size of a polycrystalline metal to submicron or even nano-size lengthscales depending on the material. During this process, the texture also changes substantially. While the strength, microstructure and formability of ECAE-deformed metals have received much attention, texture evolution and its connection with these properties have not. In this article, we cover a multitude of factors that can influence texture evolution, such as applied strain path, die geometry, processing conditions, deformation inhomogeneities, accumulated strain, crystal structure, material plastic behavior, initial texture, dynamic recrystallization, substructure, and deformation twinning. We evaluate current constitutive models for texture evolution based on the physics they include and their agreement with measurements. Last, we discuss the influence of texture on post-processed mechanical response, plastic anisotropy, and grain refinement, properties which have made ECAE, as well as other SPD processes, attractive. It is our intent to make SPD researchers aware of the importance of texture development in SPD and provide the background, guidance, and methodologies necessary for incorporating texture analyses in their studies.

Design of a novel Mn-based 1 GPa duplex stainless TRIP steel with 60% ductility by a reduction of austenite stability

Abstract: We report on the microstructure, texture and deformation mechanisms of a novel ductile lean duplex stainless steel (Fe–19.9Cr– 0.42Ni–0.16N–4.79Mn–0.11C–0.46Cu–0.35Si, wt.%). The austenite is stabilized by Mn, C, and N (instead of Ni). The microstructure is characterized by electron channeling contrast imaging (ECCI) for dislocation mapping and electron backscattering diffraction (EBSD) for texture and phase mapping. The material has 1 GPa ultimate tensile strength and an elongation to fracture of above 60%. The mechanical behavior is interpreted in terms of the strength of both the starting phases, austenite and ferrite, and the amount, dispersion, and transformation kinetics of the mechanically induced martensite (TRIP effect). Transformation proceeds from austenite to hexagonal martensite to near cubic martensite ( c ! e ! a 0 ). The e-martensite forms in the austenite with an orientation relationship close to Shoji– Nishiyama. The a 0 -martensite nucleates at the intersections of deformation bands, especially e-bands, with Kurdjumov–Sachs and