Materials Science Forum Vols. 783-786

Abstract: The effect of strain path on work hardening and texture for a super austenitic stainless steel was investigated using both experiments and modeling. Compression deformation tests by stepwise changing loading direction in two and three dimensions were performed on cubic specimens at room temperature. The results were compared to uniaxial compression with equal accumulative strain, up to 20%, and uniaxial tension with equal final strain, up to 10% elongation of the longest side. The textures in all samples were analyzed using pole figures from EBSD analysis. Because of the high stacking fault energy of this super austenitic stainless steel, the texture was dominated by <110>-fiber texture in the compressive direction for the uniaxial compression, <111>- and <100>-fiber texture in the tensile direction for the uniaxial tensile test, and a combination of all these for the cube deformation. The density of the texture was much weaker for samples where the loading direction altered, if samples with equal accumulated strain were compared. The cube deformation was also modeled using a crystal plasticity model. The crystal plasticity model consists of a representative volume element (RVE) containing crystal grains with random orientations. The Taylor assumption was used for homogenization between the macro-and subscale. The material parameters in the crystal plasticity model were determined by calibration of its macroscopic response to experimental data. The simulated textures correspond rather well to the experimental results, but the work hardening should be completed to take into account kinematic hardening.

Abstract: Electrodeposition is an advanced synthesis technique which involves the creation of a coating or free-standing material through an electrolytic process. Organic additives such as saccharin have been frequently used in electroplating operations to moderate deposit growth rates and to control film quality. In the present study, plating of Nickel without additives has resulted in a sub-microcrystalline microstructure and a <110>-fibre texture in growth direction. Structural units in form of groups of grains possessing a common <110>-zone axis in growth direction and low-Σ relationships between them have been found in the microstructure by use of EBSD. Upon annealing, grain growth sets in. However, the structural units and the texture are preserved up to 550°C. This means that the structural units stabilize the microstructure; there is no orientation change when grain growth occurs (e.g. by twinning). The low-Σ boundaries of the structural units are described in detail and texture development upon annealing is discussed in connection with results from previous studies on Ni and Ni-alloys of different initial texture.

Abstract: In the present work some new approaches have proposed for the grain oriented steel fabrication. This approach employs the new system of VC nanoprecipitates in the combination with dynamic continuous annealing for secondary recrystallization. The new system of VC inhibitors and dynamic annealing was applied to the grain oriented steel in order to obtain abnormal grain growth with Goss crystallographic orientation and considerably reduces the preparation time as the whole process lasts only several minutes. The EBSD analysis shown that suggested procedure led to evolution of the sufficiently strong {110}<001> Goss texture, which is comparable to that obtained in the conventionally treated GO steels. Moreover, the steels treated by this new method have the comparable final magnetic properties as the materials passed the conventional long – time heat treatment.

Abstract: The objective of this paper is to identify the predominant crystallographic relations between deformed state and recrystallized grains during the early stages of recrystallization of fcc metals with medium and low stacking fault energy. The experimental investigations, based on SEM/EBSD measurements, have focused on the transformations which occur in plane strain compressed single crystals with stable orientations. After annealing the disorientation across the recrystallization front 'defines' the final rotation by angles in the ranges of 25-35^o and 45-55^o around axes mostly grouped near the <122>, <012>, <112> and <111> directions located around the normals of all four {111} slip planes.

Abstract: Equal-channel angular pressing (ECAP) was applied to 16mass%Cr steel sheets for one pass prior to cold rolling in order to improve formability and alleviate ridging of the sheets. Effect of channel angle of ECAP (90° and 120°) on the deformation microstructure and the subsequent recrystallization was focused. One-pass ECAP indeed modified the cold-rolled microstructures, texture and subsequent recrystallization as compared with that in cold rolling alone. In particular, grain-scale shear bands were introduced during ECAP in otherwise hard-to-recrystallize <001>//ND grains by ECAP, and they facilitated the recrystallization. However, the effect of reducing the channel angle from 120°to 90°on the recrystallization and the formability was limited in spite of higher shear strain imposed on the sheets.

Abstract: Rolling texture evolution of pure nickel, and nickel – cobalt alloys containing 20wt.%, 40wt.%, 60wt.% cobalt content has been studied to very large true strain (ε ~ 4). The texture evolution in pure nickel and Ni-20Co was very similar, and resulted in typical Cu-type rolling texture. Microstructural analyses showed that the deformation was mostly slip dominated up to 95% beyond which it shear bands. Deformation twinning was a major deformation mechanism up to 50% reduction, and at higher strains, microstructure showed extensive shear banding. The evolution of final Goss texture in low SFE Ni-Co alloys could be explained based on the twin fraction and shear band volumes which showed grains preferably oriented towards Goss.

Abstract: The crystallographic textures of flow formed parts are of great scientific interest as they result from a complex deformation mode that comprises strain components in the axial and hoop directions. In general they resemble those of the rolling type but with slight differences. The present paper analyses the effects of certain process parameters, such as roller contact angle, feed rate, and preform hardness, since these are crucial in defining the forces acting in each principal direction of the component. Additionally, the development of a texture gradient through the wall thickness is also discussed. Texture predictions from a crystal plasticity finite-element model were also employed to support the experimental data and interpret the deformation mechanisms. Finally, the diverse nature of the flow formed textures is verified by annealing treatments at 700°C, which yields the typical gamma-fibre encountered in rolled ferritic steels upon recrystallisation in conjunction with the strengthening of the (113)[1-10] component.

Abstract: After equal channel angular pressing (ECAP) at room temperature in 08%C-18%Cr-10%Ni-Ti steel grain-subgrain structure with the size of structural elements of 100-250 nm, volume of high angle boundaries (HAB) about 59% and 38% of martensite is formed. ECAP at 400°C results in fully austenitic structure with the structural element size of 100-400 nm and volume of HAB ~54%. ECAP increases the ultimate tensile strength of 08%C-18%Cr-10%Ni-Ti steel by 1.5 - 2 times, the yield stress by 3.8 - 5.2 times, the fatigue limit - by 1.4 - 1.7 times, however the ductility is reduced. Fatigue strength is enhanced by the refinement of the structure and twinning in the austenite during ECAP and due to intensive dynamic twinning, partial martensitic transformation and increasing of the volume of HAB during cyclic deformation.

Abstract: High-Pressure Torsion (HPT) is widely used to refine the structure of metallic materials through the use of severe plastic deformation. This technique is used in this report to process different magnesium alloys using various processing conditions. The high hydrostatic pressure allows processing of these materials at room temperature without cracking. The structure was characterized and hardness distribution was determined at different areas of the processed samples. The results show significant structure refinement and increased hardness. The evolution of the structure and hardness depends on the alloying and HPT processing conditions.

Abstract: Discs of monolithic AA6061 and AA6061 reinforced with SiC_p were processed via combination of hot compaction of the mixed powders followed by high pressure torsion (HPT). HPT processing was investigated using incremental revolutions up to four, under pressures of 1 and 3 GPa. Structural evolution of the powders before and after HPT processing was investigated using scanning electron microscope (SEM). HPT processing of AA6061 discs produced a trimodel structure with micron-scale grains, subgrains and nanoscale substructure of 29, 1.9 μm, and 250 nm, respectively. Reinforcement with SiC_p resulted in a refined structure with micron-scale grains, subgrains and nanoscale substructure of 25, 1.9 μm, and 184 nm respectively. The presence of SiC_p at the triple junctions and along the grain boundaries enhanced the rate of strain hardening of the Al-matrices and significantly refined the grain size. More pronounced refinements of the grains, subgrains, and substructures were observed with increasing the HPT pressure up to 3 GPa.