Materials Science Forum Vols. 495-497

Abstract: The nucleation stage of secondary recrystallization has never been considered in detail. During the present study, nucleation of abnormal grain growth in ULC steel was studied. A specific nucleation mechanism was identified. This mechanism involved the disappearance of low angle grain boundaries, which gave rise to the onset of a local grain coalescence mechanism that clusters grains that were only separated by low angle grain boundaries. The impact of the nucleation stage remained visible in the texture that was obtained after complete abnormal grain growth.

Abstract: Dynamic recrystallization and texture development in polycrystalline copper have been investigated. Specimens were deformed in channel-die plane strain compression to true strains from 0.1 to 0.7 within the temperature range 200°C to 600°C, and the resulting microstructures were investigated with the use of high resolution electron backscatter diffraction (EBSD). Dynamic recrystallization in copper was initiated by the bulging of pre-existing high angle grain boundaries (HAGB), and occurred primarily by strain induced boundary migration (SIBM). Increasing misorientations from parent to dynamically recrystallizing grains indicated the occurrence of lattice rotations within the bulges, leading, in some cases to the formation of a HAGB behind the bulge. Discrimination between recrystallized and deformed components in material which had partially undergone dynamic recrystallization was carried out, followed by texture analysis. This revealed most of the recrystallized material to have orientations close to that of the deformed material, however, some remote orientations were observed which could not be related to the deformation texture by twin or 40° <111> relationships.

Abstract: The crystallographic relationship between the g and a phases in samples of the Gibeon meteorite and a TRIP steel was investigated by means of EBSD techniques. The orientations of the two phases were measured and are represented in pole figures. The results are compared to predictions made on the basis of the Bain, Kurdjumov-Sachs (K-S), Nishiyama-Wassermann (NW), Greninger-Troiano (G-T) and Pitsch orientation relationships. The local misorientation between individual fcc and bcc crystals along their common interface was measured to demonstrate the way in which the exact orientation relationship varies along the boundary. The local orientations within lamellae and laths of kamacite and bainite are compared to that in recrystallised ferrite polygons. The occurrence of variant selection during the transformation of deformed austenite is analyzed using a recent dislocation-based model.

Abstract: Recrystallization (RX) textures in FCC materials have defied modelling for quite a long time despite the major micro-mechanisms influencing the texture development are currently considered understood. FCC materials are coarsely classified in high and low stacking fault energy materials with a rather continuous transition between them. Both extreme kinds will give rise, after rolling deformation and later RX, to what are called Cube and Brass texture patterns. Besides long discussions, not still settled, about the influence of twinning on deformation textures, attempts of simulating RX textures have been unsuccessful. The current contribution will show SelfConsistent (SC) plus RX modelling taking into account accumulated deformation energy and misorientation angles between neighbouring crystals. Starting from grains characterized by previous SelfConsistent simulations, nucleation is probabilistically allowed on each crystal whenever the accumulated energy is larger than certain threshold. Grain boundary mobility is commanded by a probability function of the misorientation angles also calculated by the SC model. The modelling is able to predict the right trend for many of the literature experimental data without resorting to other more sophisticated variables.

Abstract: Deformation and primary-recrystallization textures in nickel alloys with some metals (Nb, to 5.4%; W, to 7.4; Re, to 4.1%; Mo, to 9.3%; V, to 10.1%; Mn, to 22.1%; Al, to 12.0% and Cr, to 22.0%) has been studied depending on the content of alloying elements and the rolling temperature. The dependence of the type of recrystallization texture on the component composition of the deformation texture has been established.

Abstract: The orientations of the inherited tetragonal (resp. cubic) variants are calculated from the parent hcp orientation in the case of a strict orientation relation. The numbering of the variants is proposed, as well as the misorientations between them. Conversely, a method for calculating the parent hcp orientation from a sufficient number of inherited variants is proposed. It is based on orientation correlating and orientation averaging, and it is particularly useful when the inherited variants are not exactly related to the parent orientation by a strict orientation relation or when the orientations of the inherited volumes slightly vary at different locations of the variant. The method is illustrated by considering the a to g phase transformation taking place in TiAl-based alloys

Abstract: Grain boundary engineering has been applied to different materials in order to increase properties particularly sensitive to intergranular phenomena. This work analyses the micromechanisms that allow the control of the amount of special boundaries which respect coincidence site lattice theory. α-brass, a lead alloy, Inconel 625 and Inconel 600 were submitted to different thermomechanical treatments and were analyzed via electron backscatter diffraction in order to characterize their grain boundaries. The occurrence of thin twins in some crystal directions during the deformation step seems to determine the results obtained as well as strain induced boundary migration.

Abstract: Texture formation during secondary recrystallization depends on the nature of secondary recrystallization process itself. So microstructure evolution and texture development during secondary recrystallization should be discussed concurrently. The main goal of the paper is studying of the effect of internal stresses on grain boundary motion or, more generally, the interaction of grain boundaries with stress fields and the effect of deformation inhomogeniety on grain boundary mobility during secondary recrystallization. Considering transformation from normal grain growth to secondary recrystallization, the attempt was made to characterize the microstructure and to relate it to the processes of nucleation and growth of new rains. The nucleation process is heterogeneous. The data allow us to assume that the nuclei are strain free grains.

Abstract: The effect of five ideal texture components ({001}<110>, {112}<110>, {111}<110>, {111}<112> and {554}<225>) typical in interstitial free (IF) steels on the development of ears was investigated using crystal plasticity finite element method (CPFEM). For the polycrystal model, the material behavior is described using crystal plasticity theory where each integration point in the element is considered to be a single grain of polycrystalline IF steel. The experimental earing profile for a IF steel was also compared to the earing profile predicted by CPFEM.

Abstract: The drawing textures of aluminum, copper, gold, silver, and Cu-7.3% Al bronze wires are approximated by major <111>+minor <100>, except silver wire, which can have the <100> texture at extremely high reductions. The <111> component in the drawing textures of aluminum, copper, gold, and silver transform to the <100> component after recrystallization. On the other hand, the <111> deformation texture of the Cu-7.3% Al bronze wire, which has very low stackingfault- energy, remains unchanged after recrystallization. The Brass component {110}<112> in rolling textures of high stacking-fault-energy metals such as aluminum and copper alloys changes to the Goss orientation {110}<001> after recrystallization. However, the Brass orientation in rolling textures of low stacking-fault-energy fcc metals such as brass appears to change to the {236}<385> orientation after recrystallization. These results seem to be related to the stability of dislocations during annealing.