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Öğe Effect of cooling conditions on the magnetic properties of bainite transformation in an Fe-2%Mn-0.5%Cr alloy(Elsevier Science Bv, 2008) Ocak, S.; Aktürk, S.; Talas, S.; Aktaş, H.The effect of cooling conditions on the magnetic properties of bainitic reaction in Fe-2%Mn-0.5%Cr alloy have been investigated using Mossbauer spectroscopy. Results showed that the bainite phase is magnetically ordered and the amount of magnetic bainite increases by decrease in grain size or increase in cooling rate. It is also shown that the retained austenite has paramagnetic behavior. The morphology of the alloy has been analyzed by using scanning electron microscopy (SEM) in heat-treated specimens at different cooling rates. In addition, the bainite start (B-s) and finish (B-f) temperatures and reverse transformation start (A(s)) and finish (A(f)) temperatures have been investigated by using differential scanning calorimetry (DSC) system for different heat treatment conditions. (C) 2008 Elsevier B.V. All rights reserved.Öğe Effect of plastic deformation on magnetic properties of Fe-40%Ni-2%Mn austenitic alloy(Journal Iron Steel Research Editorial Board, 2007) Büyükakkaş, Selva; Aktaş, H.; Aktürk, S.The effects of plastic deformation on the magnetic properties of austenite structure in an Fe-40%Ni-2%Mn alloy is investigated by using Mossbauer spectroscopy and Differential Scanning Calorimetry (DSC) techniques The morphology of the alloy has been obtained by using Scanning Electron Microscopy (SEM). The magnetic behaviour of austenite state is ferromagnetic. After plastic deformation, a mixed magnetic structure including both paramagnetic and ferromagnetic states has been obtained at the room temperature. The volume fraction changes, the effective hyperfine fields of the ferromagnetic austenite phase and isomery shift values have also been determined by Mossbauer spectroscopy. The Curie point (Tc) and the Neel temperature (T-N) have been investigated by means of DSC system for non-deformed and deformed Fe-Ni-Mn alloy. The plastic deformation of the alloy reduces the T-N and enhances the paramagnetic character of austenitic Fe-Ni-Mn alloy.Öğe Isothermal martensite formation in a magnetically ordered austenite phase of an Fe-32%Ni-0.4%Cr alloy(Elsevier Science Sa, 2005) Aktürk, S.; Güner, M.; Aktaş, H.In this study, the isothermal martensitic transformation has been examined in an austenitic Fe-Ni-Cr alloy. The magnetic properties of the austenite phase are investigated with Mossbauer spectroscopy and the results showed that the Fe-32%Ni-0.4%Cr alloy in the austenite state is magnetically ordered. In the austenite state, the six peaks of the ferromagnetic phase of Fe-32%Ni-0.4%Cr alloy were observed in the Mossbauer spectrum. The effective hyperfine field of the ferromagnetic (or antiferromagnetic) austenite phase was determined as 31.9 T and the isomer shift value was determined as -0.19 mm/s. We also investigated the austenite-martensite phase transformation observed upon cooling in the Fe-Ni-Cr alloy by scanning electron microscopy (SEM). (C) 2004 Published by Elsevier B.V.Öğe Mossbauer studies on an AISI 1137 type steel(Indian Acad Sciences, 2006) Güler, Emre; Aktaş, H.An AISI 1137 type medium carbon steel was studied by means of scanning electron microscopy and Mossbauer spectroscopy. This steel in as received state at room temperature was ferritic. Different heat treatments on related steel exhibited different microstructures such as pearlite and bainite. Also magnetism of these product phases was determined as 32.7 T and 32.6 T relatively where ferromagnetism of ferritic phase in as received state was 33.05 T. Mossbauer parameters such as isomer shifts and % volumes were also determined before and after transformations.Öğe Some aspects of thermally induced martensite in Fe-30% Ni-5% Cu alloy(Elsevier Science Bv, 2007) Güner, M.; Güler, E.; Yaşar, E.; Aktaş, H.Kinetical, morphological, crystallographical and several thermal properties of thermally induced martensite in the austenite phase of Fe-30% Ni-5% Cu alloy were investigated. Scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) techniques were used during study. Kinetics of the transformation was found to be as athermal type. SEM and TEM observations revealed alpha' (BCC) martensite formation in the austenite phase of alloy by thermal effect. These thermally induced alpha' martensites exhibited a thin plate-like morphology with twinnings. (C) 2007 Elsevier B.V. All rights reserved.
