Papers by Keyword: Severe Deformation

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Authors: Minoru Umemoto, Yoshikazu Todaka, Yukinori Watanabe, Jin Guo Li, Koichi Tsuchiya
Authors: Alexander Spuskanyuk, Yan Beygelzimer, Viktor Varyukhin
Authors: Jong Kap Kim, Woo Jin Kim
Abstract: Equal-channel angular pressing (ECAP) is an efficient method of improving strength of metallic alloys through (sub) grain refinement to, typically, the sub-micrometer level by introducing intensive plastic strain into materials through repetitive pressing. In the present study, the post-ECAP aging effect on strength of age hardenable aluminum alloys (6061, 2024, 7075 Al) was examined and it could be concluded that pre-ECAP solid solution treatment combined with post-ECAP low-temperature aging provided much more significant room-temperature strengthening effect than conventional ECAP processing routes without involving special heat treatments.
Authors: Jozef Zrník, Libor Kraus, Miroslav Cieslar, Peter Sláma
Abstract: In this study, the relationship between the structure and properties of commercial purityaluminium (AW-1199) was investigated by applying constrained groove pressing (CGP) method.The refinement of the coarse grain aluminium microstructure to submicrocrystalline size by largeplastic strain at room temperature defined. The impact of various strains upon microstructurechanges is investigated using transmission electron microscopy (TEM) and electron back scatterdiffraction (EBSD). A mixture of subgrains produced by grains subdivision and polygonizedsubgrains formed locally due to dynamic recovery was found in the deformed aluminium. Thetensile properties and resulting hardness are related to microstructural evolution induced by CGP. Asubstantial impact of straining upon the increasing in tensile strength was observed after the firstpass. Further strain increase had an insignificant effect on tensile strength but was accompanied byductility loss. The post deformation annealing effect was then explored with aim to increase theductility. The results indicate that changes in strength and ductility may be related to formation of abimodal structure.
Authors: Ulrich Froebel
Abstract: Forged and extruded TiAl products suffer from structural and chemical inhomogeneities that reduce the reliability of components. In an attempt to improve the homogeneity of the material, the feasibility of cyclic axial deformation and cyclic torsional deformation superimposed with compression, where much higher strains can be imparted into the material than during forging and extrusion, were investigated. Accordingly, during torsion superimposed with compression pronounced shear localization and cracking occurs. These difficulties can largely be overcome by cyclic axial deformation.
Authors: Ho Sup Sim, Kon Bae Lee, Hyung Ryul Yang, Hoon Kwon
Abstract: Effect of the severe deformation by multi-pass rolling on microstructure and tensile properties was analyzed in terms of rolling temperature, plate thickness, and cooling rate for a modified API X65 steel containing B. The plates, 80 and 50 mm thickness, were rolled six times by 20%/pass (total 75%) to 20 and 12 mm, at 1023 K of unrecrystallized γ region or 973 K of intercritical (α+γ) region, and then quenched in water or oil. All specimens except one oil-quenched condition showed relatively high UTS 700-830 MPa and the continuous yielding(YR~0.6), typical mode of the (ferrite + martensite (bainite)) dual phase microstructure. In contrast, one oil-quenched specimen with the 973 K-20 mm condition, exhibited the discontinuous yielding (YR~0.8), indicating that the microstructure basically consists of ferrite plus pearlite, as well as a relatively low UTS 660 MPa. The degree of deformation really occurring within materials, i.e., strain hardening seems to be enhanced with a decrease in deformation temperature. As the degree of deformation increases, the remaining austenite, not dynamically transformed to fine ferrite, becomes increasingly unstable. A lower hardenability of this remaining austenite thus would lead to a higher possibility to transform into the (ferrite + pearlite) structure of lower strength rather than the (ferrite + martensite (bainite)) of higher strength.
Authors: Ho Sup Sim, K.S. Lee, Kon Bae Lee, Hyung Ryul Yang, Hoon Kwon
Abstract: Secondary hardening and fracture behavior in the high Co-Ni steels containing W, has been studied in terms of severe deformation, Cr addition, and austenite condition. Two kinds of Co- Ni steels, containing the only W(W steel), and the W and Cr(WCr steel), were severely rolled and followed by direct quenching(DQ). In comparison with undeformed specimens, reaustenitizing( RA) was performed. DQ specimens exhibited higher impact toughness as well as higher hardness, as compared to RA specimens. The aging kinetics of the WCr steel was accelerated due to the Cr addition. While the W steel showed the intergranular embrittlement in the high temperature RA condition, in addition, the WCr steel exhibited the transgranular mode of mostly dimple type.
Authors: Fuqian Yang, Lingling Peng, Kenji Okazaki
Abstract: The localized deformation behavior of annealed Al and Al severely deformed by ECAE process was determined by using microindentation test. Using the method proposed by Tabor, the indentation stress-strain curves of annealed Al and as-ECAE deformed Al were constructed, which display similar work-hardening behavior. For annealed Al, the altitude of the indentation stressstrain curves is a function of the indenter size. A master curve then is constructed, which displays different work-hardening behavior. For the ECAE deformed Al, the indentation stress-strain curves are independent of the indenter size, suggesting that the microstructure inside the as-ECAE deformed Al is different from the annealed Al.
Authors: Ho Sup Sim, Ki Seop Cho, Kon Bae Lee, Hyung Ryul Yang, Hoon Kwon
Abstract: Applying the severe deformation, the mechanical properties related to secondary hardening were investigated. The Mo-Cr-Co-Ni steels containing (5-13)wt% Co and (8-14)wt% Ni were severely rolled at 850 °C, followed by direct quenching(DQ). DQ specimens were then isothermally aged at 475°C. Ni additions promoted aging kinetics, accompanied by a little enhancement in hardness. In contrast, Co additions enhanced the peak hardness, but did not induce a remarkable aging acceleration. In the 13Co addition group, an actual secondary hardening, that is, the peak hardness is higher than the as-quenched hardness. Variation in peak hardness(Rc) in alloys is summarized as follows; 14Ni-13Co(57.2) ≒ 11Ni-13Co(57.1) > 8Ni-13Co(56.5) > 11Ni- 9Co(56.2) > 8Ni-9Co(54.4) > 11Ni-5Co(53.4).
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