Fundamentals of Deformation and Annealing

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Authors: Yuriy Perlovich, Margarita Isaenkova, Vladimir Fesenko
Abstract: The substructure inhomogeneity of real textured metal materials was studied by use of the X-ray method of Generalized Pole Figures. Main regularities of substructure inhomogeneity were revealed for the first time. Substructure conditions of grains in rolled material form an extremely wide spectrum and vary by passing from texture maxima to texture minima, where residual deformation effects are most significant. The distribution of residual elastic microstrains in the orientational space of rolled material shows the distinct cross-wise system, consisting in alternation of quadrants with predominant microstrains of opposite signes.
Authors: A.Ya. Kochubey, Vladimir Serebryany, V.N. Timofeev
Abstract: Ductility of Mg – alloys is linked to a shortage of independent slip systems. Basaltextured samples of Mg-Al-Zn alloy are examined for presence of dislocations of different types after hot compression tests of cast samples and cold compression tests of hot-rolled samples. The JEM-1000, electron transmission microscope with an accelerating voltage of 750 kV using a dark field–weak beam method of observation and the g·b=0 invisibility criterion as a basic method of the analysis of Burgers vectors, is used to analyse the samples. Dislocations with Burgers vectors , [c] and are found. The results are used to evaluate the dislocation density and determine the possible dislocation reactions.
Authors: Roumen H. Petrov, Leo Kestens, Yvan Houbaert
Abstract: TRIP-assisted steel with a composition of 0.2%C, 1.5%Mn, 1.5% Al was studied in the undeformed state and after the application of 20% tensile strain parallel to rolling the direction of the sheet. The microstructure and microtexture of the steel sheets were examined in detail by means of electron backscattered diffraction (EBSD) in order to quantify the microstructural constituents and to study the strain distribution. The evolution of the microtexture and the distribution of the specific texture components between the BCC and FCC phases were studied as a function of the external strain. The strain localization and strain distribution between the structural constituents were quantified on the base of the local misorientation maps. The full constraint Taylor model was used to predict the texture changes in the material and the results were compared to the experimental findings. Comparing the local misorientation data it was found that at low strains the ferrite accommodates approximately 10 times more deformation than the retained austenite. The strain localizes initially on the BCC-FCC phase boundaries and then is spread in the BCC constituents (ferrite and bainite) creating a deformation skeleton in the BCC phase. The composite-like strengthening behaviour in TRIP-aided steel at 20% deformation might be expressed by the decreasing free path of dislocations in ferrite due to the enlarging and thickening of the multiphase skeleton as plastic deformation progresses, without changing significantly the main texture components in the material.
Authors: Hiromi Miura, Taku Sakai, Takanori Ueno, Nobuhiro Fujita, Naoki Yoshinaga
Abstract: A Ni-30 mass% Fe alloy with dispersed coarse oxide particles, ranging from 1 to 3 μm in diameter, was multi-directionally forged (MDF) at temperatures between 773 K and 873 K at a true strain rate of 1 x 10-3 s-1 in vacuum. For comparison, a particle-free Ni-Fe alloy was also prepared and MDFed. At 873 K, an obvious flow softening occurred during MDF especially in the alloy with dispersed particles, while work hardening followed by steady-state flow appeared at 773 K in both alloys. With increasing cumulative strain, the average grain size became gradually finer. However, the evolved microstructure was quite different depending on temperature and dispersion of particles. At 873 K, in the alloy with particles, equi-axed fine grains of about 1.3 μm in average was uniformly evolved at a cumulative strain of Σε = 2.4, while at 773 K the microstructure was still inhomogeneous. The above experimental results suggest important role of coarse particles to stimulate grain refinement.
Authors: Martin Hafok, Reinhard Pippan
Abstract: By using techniques of severe plastic deformation a metallic material can be subjected to an enormous strain that is not achievable by conventional methods of deformation. In this study nickel single crystals with different crystallographic orientation and nickel polycrystals were deformed by high pressure torsion. All nickel samples were processed up to the evolution of a saturation microstructure where no further hardening of the material can be observed. In this region all samples develop a similar microstructure and micro-texture. The differences in the fragmentation of the microstructure and the micro-texture development between the single crystals and the polycrystalline aggregate were examined using EBSD. A major difference between single crystals and polycrystals was not only the microstructure evolution at low equivalent strains, but also the development of a stable micro-texture, which is achieved earlier by the use of a polycrystalline aggregate.
Authors: J. Kusnierz
Abstract: The changes in the tensile properties, in relation to the phenomenon of shear banding are investigated in copper, rolled at liquid nitrogen temperature and then recrystallized, after initial processing by Equal-Channel Angular Extrusion (ECAE) at room temperature. Increases in ductility and strength up to the fourth pass of ECAE processing were noted, then a decrease of both properties was observed. The decrease was accompanied by twinning and shear banding. In rolled samples, pre-cooled down to the temperature of liquid nitrogen and initially recrystallized, the twinning and shear banding mechanisms were the most probable mechanisms responsible for lowering the mechanical properties.
Authors: Suk Hoon Kang, Jae Hyung Cho, Joon Sub Hwang, Jong Soo Cho, Yong Jin Park, Jung Tak Moon, Kyu Hwan Oh
Abstract: Cold drawn gold wires are widely applied in electronic packaging process to interconnect micro-electronic components. They basically provides a conducting path for electronic signal transfer, and experience thermo-mechanical loads in use. The mechanical stability of drawn gold wires is a matter of practical concern in the reliable functioning of electronic devices. It is known that mechanical properties of materials are deeply related to the microstructure. With appropriate control of deformation and heat processes, the mechanical properties of final products, such as tensile strength and elongation can be improved. Severe plastic deformation by torsion usually contributes to grain refinement and increment of strength. In this study, microstructure variations with torsion strain followed by drawing and heat treatment were investigated. Analyses by focused ion beam (FIB) and electron backscattered diffraction (EBSD) were carried out to characterize the effect of deformation and heat treatment on the drawn gold wires. Pattern quality of EBSD measurements was used as a quantitative measure for plastic deformation.
Authors: O.V. Mishin, Andrew Godfrey
Abstract: Microstructure and boundary populations were investigated in a superplastic Al-5.5%Mg- 2.2%Li-0.12%Zr alloy hot-deformed by equal channel angular extrusion. The microstructure was found to be inhomogeneous and revealed deformation structures being subdivided by both low- and high-angle boundaries.
Authors: A.W.F. Smith, D.N. Crowther, P.J. Apps, Philip B. Prangnell
Abstract: It is well known that the refinement of grain size in metals leads to a significant improvement in specific mechanical properties. Processing schedules have been investigated aimed at producing an homogeneous ultra-fine ferrite and spheroidised carbide aggregate microstructure in high carbon (CMn) steels (0.6-1.2wt%C), via conventional ‘warm’ rolling and innovative Equal Channel Angular Extrusion (ECAE). Suitable deformation schedules were determined from dilatometry and thermo-mechanical Gleeble simulations. Evidence of an ultra-fine ferrite and carbide aggregate microstructure following ‘warm’ rolling was observed. A significant improvement in tensile strength, particularly proof stress was also noted in comparison to material deformed at higher temperatures. Concurrent ECAE experiments investigated microstructural evolution with incremental strain. Extensive analysis was carried out using various techniques, including high resolution Electron Back Scattered Diffraction (EBSD). Evidence of ferrite grain refinement was noted in a eutectoid composition steel. A sub-micron ferrite structure was observed following high strains (ε~3.33) and the mechanical properties exhibited a marked increase in tensile strength.
Authors: S.L.A. Valcke, M.R. Drury, J.H.P. de Bresser, G.M. Pennock
Abstract: Calcite deformed by high temperature creep develops a heterogeneous microstructure consisting of deformed and recrystallised grains. The deformed grains either contain homogeneously distributed subgrains of similar size, or heterogeneously distributed small subgrains at grain boundaries (mantle subgrains) and relatively large subgrains in the core of grains (core subgrains). This paper demonstrates a method using electron backscattered diffraction (EBSD) to distinguish between the different types of grains and subgrains and to measure their sizes separately. In geological materials the average subgrain size, regardless of the subgrain type, is often used to estimate the deformation stress. However, this paper shows that mantle and core subgrain types only show a weak or no stress dependence.

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