Papers by Keyword: Ultrafine Grained Material

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Authors: Tibor Kvačkaj, Robert Kočiško, Michal Besterci, T. Donič, Imrich Pokorný, T. Kuskulič, Katarína Sülleiová, M. Molnárová, A. Kováčová, Michal Kvačkaj
Abstract: Equal channel angular pressing (ECAP) is a material processing method for developing an ultrafine-grained (UFG) structure by introducing severe plastic deformation (SPD) in a bulk material with no changes in its cross-section. Numerous analytical and numerical studies on equal channel angular pressing have been performed in recent years. The present work focuses on the effects of die geometry width is defined by the angle between two channels Φ, angle on outer corner of die Ψ (or radius R) and angle within internal corner (or radius r) of die on average effective strain after one pass route. Next, there are analyses of strength properties, plastic properties, fracture mechanism, as well as analyses of Cu structure evolution after SPD by ECAP technology, in the paper. The sixteen passes through the ECAP matrix were realized using route C. The following experimental results and their analyses, the biggest increase of strength and microhardness was proved already after 4th pass. Valuation of fracture surfaces shows that after 12th pass plastic fracture is transformed from transcrystalline ductile mixed fracture. After 4th pass, the avarage grain size decreased from initial approximate size 7 µm to 200 nm, whereby the average grain size was changeless after subsequent deformations. Possible mechanism of high-angle boundary nanograins evolution consists of formation of cell structure, subgrains that transform with the increase of deformation into nanograins with big-angle misorientation.
Authors: Yan Beygelzimer, O. Prokof'eva, R. Kulagin, Viktor Varyukhin, Sergey Synkov
Abstract: It is shown that for ultrafine grained materials obtained with severe plastic deformation methods, the value of elongation up to fracture does not determine ductility, while the reduction of area up to fracture does determine it. The latter characteristic gives information about how an alloy structure resists the formation of discontinuity flaws under deformation in a hard stress state. We show that for a commercial grade titanium that underwent Twist Extrusion (TE), the value of , and thus ductility, is higher in the UFG state than in the coarse-grained state.
Authors: Taro Maekawa, Hiromoto Kitahara, Nobuhiro Tsuji
Abstract: Microstructures and mechanical properties of Fe-15wt.%Cr-10wt.%Ni alloy ARB processed by various cycles were studied. The starting material showed lath martensite structure. However, the austenitic phase became stable by the high straining (ARB) above Af temperature. The volume fraction of austenitic phase greatly increased to around 90 % by 2 ARB cycles and nearly saturated at about 95 % after higher ARB cycles. The grain refinement progressed during the ARB, which leaded to the formation of ultrafine lamellar UFG austenitic microstructure with mean lamellar spacing of about 300 nm. The UFG Fe-Cr-Ni alloy performed both high strength and large elongation. Especially, the yield strength of the alloy ARB processed by 5 cycles reached to 900 MPa, and the total elongation was 40 %. The good ductility of the present specimens was attributed to the occurrence of transformation-induced plasticity (TRIP).
Authors: Igor V. Alexandrov, Roza G. Chembarisova
Abstract: A grain size is known to be one of the factors which define mechanical properties of metallic materials. At the same time the mechanisms which regulate the deformation behavior of bulk ultrafine-grained (UFG) metals produced by the severe plastic deformation method are still a subject for intensive study and fixed ambiguously. The report presents the developed model and the results of its application for kinetic modeling of the deformation behavior of coarse-grained (CG) and UFG Ti. Modeling has been carried out considering the possible contribution of dislocation slip and ageing. Conclusions about the role of the investigated mechanisms in the appearance of the peculiarities of the deformation behavior of CG and UFG Ti have been made.
Authors: Petr Král, Jiří Dvořák, Vàclav Sklenička
Abstract: Experiments were conducted on an Al-0.2wt.%Sc alloy to evaluate the effect of equalchannel angular pressing (ECAP) on its creep behaviour. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route BC up to 8 ECAP passes. Creep tests in tension were performed on the as-pressed samples at 473 K under an applied stress range between 10 to 50 MPa. For comparison purposes, some creep tests were performed also on the unpressed alloy. Following ECAP and creep testing, samples were prepared for examination by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back scattering diffraction (EBSD) unit. The observation of the surface of the ECAPed samples after creep exposure showed the occurrence of mesoscopic shear bands. The EBSD data reveal that these bands are separated by high angle grain boundaries. The creep resistance of an alloy is a little decreased after one ECAP pass. However, successive ECAP pressing lead to a noticeable decrease of the creep properties. Thus, the Al-0.2wt.%Sc alloy processed by 8 ECAP passes exhibited faster creep rate by about two and/or three orders of magnitude than the unpressed alloy when creep testing at 473 K and at the same applied stress. The detrimental effect of ECAP on the creep resistance is probably a consequence of a synergetic effect of mesoscopic sliding of groups of grains along shear bands, more intensive grain boundary sliding and creep cavitation in creep of the ultrafine-grained material.
Authors: Dmitriy Gunderov, Alexander Lukyanov, Egor Prokofiev, Anna Churakova, Vladimir Pushin, Sergey Prokoshkin, Vladimir Stolyarov, Ruslan Valiev
Abstract: The article represents results of influence of different severe plastic deformation (SPD) techniques on TiNi alloys. It is demonstrated that strength and shape memory effect (SME) of TiNi can be significantly enhanced due to formation of ultrafine-grained (UFG) and nanocrystalline (NC) structures by SPD. Influence of equal channel angular pressing (ECAP), high pressure torsion (HPT), multi-step SPD deformations (ECAP plus cold rolling) on structure, mechanical and functional properties of TiNi alloys is considered. There are represented first results of influence of equal channel angular pressure-Conform (ECAP-C) on TiNi alloys, which is a perspective technology for industrial fabrication of UFG metals and alloys.
Authors: B. Baudelet, J. Languillaume, G. Kapelski
Authors: Hyoung Seop Kim, Min Hong Seo, Sun Ig Hong, Hong Rho Lee, Byong Sun Chun, Kap Ho Lee
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