Papers by Keyword: Ultrafine Grained Material

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Authors: Ke Jing Yang, Yulia Ivanisenko, J. Markmann, Hans Jorg Fecht
Abstract: In situ tensile tests were conducted on ultra fine grained (UFG) pure Pd and Pd-x% Ag (x=20, 60) alloys of different stacking fault energies (SFEs) with the aim to study the general features of the deformation process of UFG materials as well as the peculiarities brought by the alloying. Grey scale correlation analysis (GSCA) was used to determine the true strain as well as the surface flow within the gauge length. It was shown that the largest values of strength and uniform elongation were obtained in Pd-20% Ag alloy. The GSCA revealed different macroscopic flow processes in this sample as compared with pure Pd and Pd-60% Ag alloy. In particular, pure Pd and Pd-60% Ag alloy demonstrated rapid localization of plastic flow in the neck area, whereas Pd-20% Ag samples showed a large contribution of homogenous deformation even after neck formation. It has been proposed that larger strain hardening capacity of Pd-20% Ag alloy is related to its lower SFE as compared with that of pure Pd: the lower is the SFE, the more difficult is the cross slip and climb of split dislocations, which leads to enhanced dislocation storage and, ultimately, to increased strain hardening. At the same time, further decrease of SFE in Pd-60% Ag sample leads to development of deformation twinning and consequent reduction of strain hardening. The dimpled structure of fracture surfaces in the samples will also be discussed in relationship to these findings.
Authors: Miroslav Karlík, Margarita Slámová, Petr Homola, P. Sláma, Miroslav Cieslar
Abstract: Mechanical properties and microstructure of twin-roll cast (TRC) pure aluminium, Al-Fe-Mn-Si (AA8006) and Al-Mg (AA5754) alloy sheets ARB processed at ambient and elevated temperatures (200, 250, 300 and 350°C) were investigated. Processing at elevated temperatures results in better bonding but it produces smaller increases in hardness. AA8006 specimens were processed without any problems up to 7 cycles. The alloy AA5754 suffered from severe edge and notch cracking since the first cycle. The strength was evaluated from tensile test and microhardness measurements; the microstructure was examined using light microscopy, and transmission electron microscopy. The microstructure was compared to that of conventionally cold rolled (CCR) specimens with true strain ε of 0.8, 1.6, 2.4 and 3.2 corresponding to the strain induced by 1 to 4 ARB cycles. The work hardening of alloy AA8006 saturated after the 3rd cycle, whereas the hardness of alloy AA5754 increased steadily up to the 5th cycle. Very fine grain structure with large fraction of high angle boundaries was observed in both alloys after two cycles of ARB. The grains were refined to submicrometre and nanometre size (down to 90 nm in alloy AA5754). Intensive post-dynamic recovery was observed in AA8006 specimens. The recovery is less pronounced in the AA5754 alloy with high concentration of solute atoms in solid solution.
Authors: Hyoung Seop Kim
Abstract: Equal channel angular pressing (ECAP) is a convenient forming procedure among various severe plastic deformation processes. It is based on extruding material through specially designed entry and exit channel dies to produce an ultrafine grained microstructure. The properties of the materials obtained depend on the plastic deformation behaviour during ECAP, which is governed mainly by the die geometry, the material itself and the processing conditions. As the mechanical properties of the severely deformed material are directly related to the deformation history, understanding the phenomena associated with strain and strain rate development in the ECAP process is very important. In this study, the results of continuum modelling of ECAP are described in order to understand strain and strain developments. For this purpose, the results of modelling ECAP using the finite element method and analytical solution are presented for various geometric conditions. It was concluded that although deformation is nonuniform due to geometric effects, the strain and strain rate values obtained by the analytical solutions are not much different from the average results of the finite element method.
Authors: Dong Hyuk Shin, Jong Ryoul Kim, Yong Jun Oh, Kyung Tae Park
Authors: Anna Urbańczyk-Gucwa, Kinga Rodak, Adam Płachta, Joanna Sobota, Zbigniew Rdzawski
Abstract: The results of the microstructure and hardness investigations of the Cu-0.8Cr alloy after application of severe plastic deformation (SPD) implemented by rolling with the cyclic movement of rolls (RCMR) are presented in this paper. Performed substructure investigations showed that using the RCMR method can refine the microstructure of Cu-0.8Cr alloy to the ultrafine scale. The structure of the Cu-0.8Cr alloy was analyzed using light microscope (LM) and scanning transmission electron microscope (STEM). The quantitative studies of the substructure was performed with "MET-ILO" software, on the basis of images acquired on STEM microscope.
Authors: Radik R. Mulyukov, Ayrat A. Nazarov, Renat M. Imayev
Abstract: Principles of fabrication of ultrafine grained bulk and sheet materials for superplastic deformation by the methods of multiple isothermal forging and warm rolling are formulated. New data on superplastic behaviour of commercial alloys, on diffusion bonding of similar and dissimilar materials, and superplastic forming of titanium alloys are presented. The recent application of the diffusion bonding and superplastic forming technology for the production of hollow blades is demonstrated.
Authors: Michael Sevier, Seongeyl Lee, M. Ravi Shankar, Henry T.Y. Yang, Srinivasan Chandrasekar, W. Dale Compton
Abstract: The deformation field associated with chip formation in plane strain (2-D) machining has been simulated using the finite element method (FEM), with the objective of developing 2-D machining as an experimental technique for studying very large strain deformation phenomena. The principal machining parameters are the tool rake angle, cutting velocity and the friction at the toolchip interface while the deformation field parameters are strain, strain rate and temperature. The relation between rake angle and the shear strain in the deformation zone is studied for the low-speed cutting of lead. This correspondence is validated by comparison with measurements of the deformation parameters made by applying a Particle Image Velocimetry (PIV) technique to highspeed photographic image sequences of the deformation. It is shown that plastic strains in the range of 1-15 can be realized in a controlled manner by appropriate choice of the rake angle. The unique capabilities offered by 2-D machining for studying micro- and nano- mechanics of large strain deformation, and the creation of ultra-fine grained materials are highlighted in the context of these results.
Authors: Ruslan Valiev, Rinat K. Islamgaliev, N.F. Yunusova
Authors: Emmanuel Bouzy, Jean-Jacques Fundenberger, Thierry Grosdidier
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