M. Wroński

FCC Rolling Textures Reviewed in the Light of Quantitative Comparisons between Simulated and Experimental Textures

The crystallographic texture of metallic materials has a very strong effect on the properties of the materials. In the present article, we look at the rolling textures of fcc metals and alloys, where the classical problem is the existence of two different types of texture, the “copper-type texture” and the “brass-type texture.” The type of texture developed is determined by the stacking fault energy of the material, the rolling temperature and the strain rate of the rolling process. Recent texture simulations by the present authors provide the basis for a renewed discussion of the whole field of fcc rolling texture. We simulate the texture development with a model which allows us to vary the strength of the interaction between the grains and to vary the scheme for the calculation of the lattice rotation in the individual grains (type CL/MA or PR/PSA). For the deformation pattern we focus on {111}<110> slip without or with deformation twinning, but we also consider slip on other slip planes and slip by partial dislocations. We consistently make quantitative comparison of the simulation results and the experimental textures by means of a scalar correlation factor. We find that the development of the copper-type texture is best simulated with {111}<110> slip combined with type CL/PR lattice rotation and relatively strong interaction between the grains — but not with the full-constraint Taylor model and neither with the classical relaxed-constraint models. The development of the brass-type texture is best simulated with {111}<110> slip combined with PR/PSA lattice rotation and weak interaction between the grains. The possible volume effect of deformation twins on the formation of the brass-type texture is a controversial question which we discuss on the basis of our simulations as seen together with other investigations.

New Concept for VFTO Attenuation in GIS with Modified Disconnector Contact System

This paper investigates on a new concept for very-fast transient overvoltages (VFTOs) attenuation in gas-insulated switchgear (GIS). The concept, first introduced by the authors in this paper, involves modification of the GIS disconnector contact system in order to dissipate the VFTO energy in damping elements placed inside the GIS busbar conductor. The concept is an alternative to the state-of-the-art method where magnetic rings are placed in the space between the GIS conductor and the enclosure. The proposed arrangement has no impact on the damping element on the dielectric design of the GIS busbar, and it highly reduces the impact on the GIS thermal design. This paper presents analyses which show feasibility of the concept, through 1) principles which govern voltage conditions inside the GIS busbar and 2) full-Maxwell finite-element method electromagnetic simulations of VFTO attenuated with the use of the proposed concept.

Crystallographic Textures Variation in Asymmetrically Rolled Steel

The crystallographic texture formation in low carbon steel during asymmetric rolling was studied experimentally and analysed numerically. Modelling of plastic deformation was done in two scales: in the macro-scale using the finite element method ( FEM) and in crystallographic scale using the polycrystalline deformation model (LW model). The stress distribution in the rolling gap was calculated using FEM and next these stresses were applied in LW model of polycrystalline plastic deformation. In general, the predicted textures agree very well with experimental ones.

Effect of rolling asymmetry on selected properties of grade 2 titanium sheet

Asymmetric rolling can be used in order to modify material properties and to reduce forces and torques applied during deformation. This geometry of deformation is relatively easy to implement on existing industrial rolling mills and it can provide large volumes of a material. The study of microstructure, crystallographic texture and residual stress in asymmetrically rolled titanium (grade 2) is presented in this work. The above characteristics were examined using the EBSD technique and X-ray diffraction. The rolling asymmetry was realized using two identical rolls, driven by independent motors, rotating with different angular velocities. It was found that asymmetric rolling leads to microstructure modification and refinement. At low deformations one observes a process of grain size decrease caused by the asymmetry of rolling process. In contrast, at the medium range of deformations the microstructure refinement consists mainly in subgrain formation and grain fragmentation. Another observation is that for low to intermediate rolling reductions (≤40%) the predominant mechanisms are slip and twinning, while for higher deformation (>40%) the main mechanism is slip. It was found that grain refinement effect, caused by the rolling asymmetry, persists also after recrystallization annealing. And finally, texture homogenization and reduction of residual stress were confirmed for asymmetrically rolled samples.

Study of texture, microstructure and mechanical properties of asymmetrically rolled aluminium

Asymmetric rolling is a promising forming technique offering numerous possibilities of material properties modification and the improvement of technological process parameters. This geometry of deformation is relatively easy to implement on existing industrial rolling mills. Moreover, it can provide large volume of a material with modified properties. The study of microstructure, crystallographic texture and mechanical properties of asymmetrically rolled aluminium is presented in this work. The above characteristics were examined using EBSD technique and X-ray diffraction. The rolling asymmetry was realized using two identical rolls, driven by independent motors, rotating with different angular velocities. It was found that asymmetric rolling leads to microstructure refinement, texture homogenization and decreasing of residual stress.

Study of Microstructure, Texture and Residual Stress in Asymmetrically Rolled Titanium

Asymmetric rolling is a promising forming technique offering numerous possibilities of material properties modification and the improvement of technological process parameters. This geometry of deformation is relatively easy to implement on existing industrial rolling mills. Moreover, it can provide large volume of a material with modified properties. The study of microstructure, crystallographic texture and residual stress in asymmetrically rolled titanium (grade 2) is presented in this work. The above characteristics were examined using EBSD technique and X-ray diffraction. The rolling asymmetry was realized using two identical rolls, driven by independent motors, rotating with different angular velocities ω1 and ω2. This ensured a wide range of rolling asymmetry: A=ω1/ω2. It was found that a strong shear stress induced in the asymmetrically rolled material allowed to obtain a microstructure refinement, texture homogenization and lowering of residual stress.

On the lattice rotations accompanying slip

Abstract The texture (crystallographic texture) of a polycrystalline material is the statistical representation of the preferred orientation of the crystal lattices in the various grains. The great majority of the materials that we encounter do have a texture, some degree of preferred orientation of the crystal lattices, and this texture may have a strong effect on the properties of the materials. The texture is introduced by lattice rotations in the individual grains during processing. The present critical assessment deals with the lattice rotations during rolling of face centred cubic (fcc) metals and alloys. Sixteen years ago, a modification of the traditional procedure for the calculation of these lattice rotations was suggested, a modification that would permit a realistic modelling of the development of the brass type texture, one of the two types of texture developed during rolling of fcc materials. However, this modification was not given serious consideration by the texture community. Recently, two new independent investigations have supported the modification. We argue that this new situation should lead to a general acceptance of the modification, and we discuss the scientific and technological aspects of the modification. We also discuss possible modifications beyond that of the original suggestion.

Asymmetric rolling textures of aluminium studied with crystalline model implemented into FEM

The goal of this work was to study the asymmetric rolling process using the Finite Element Method (FEM) coupled with the deformation model of polycrystalline material. The Leffers-Wierzbanowski (LW) model was selected to be implemented into FEM. This implementation enables a study of heterogeneous plastic deformation process, like asymmetric rolling, taking into account its crystallographic nature. Our aim was to examine the crystallographic texture and mechanical properties of asymmetrically rolled aluminium 6061. The simulation results are compared with experimental textures determined by X-ray diffraction. The advantages of asymmetrical rolling over symmetrical rolling are reduced rolling normal forces and rolling torques, improvement of microstructure and producing the homogeneous crystallographic texture.

Study of Asymmetric Rolling of Titanium by the Finite Elements Method with Implemented Crystalline Model

The goal of this work was to study the asymmetric rolling process using the Finite Element Method (FEM) coupled with the deformation model of polycrystalline material. The Leffers-Wierzbanowski (LW) model was selected to be implemented into FEM. This implementation enables a study of heterogeneous plastic deformation process, like asymmetric rolling, taking into account its crystallographic nature. The asymmetric rolling was realized using two identical rolls, driven by independent motors, rotating with different angular velocities. This enabled to obtain a controlled range of rolling asymmetry. Our aim was to examine the properties of asymmetrically rolled commercially pure titanium (Grade 2).

Some Comments on Lattice Rotation in Aspect of Brass-Copper Texture Transition

The classical definition of lattice rotation leads in some cases to different textures than the definition based on the preservation of orientations of selected sample directions and/or planes. For example, if classical {111} slip is taken into account for f.c.c. materials, the former approach enables to predict both copper and brass types of rolling texture, while classical approach predicts only the first one. The analysis of rolling texture formation is done for two types of lattice rotation in function of grain-matrix interaction parameter used in a deformation model. Predicted textures and correlation factors estimating the similarity of predicted and experimental textures are presented.