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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 The magnetic properties of martensitic phase in Fe-Ni-Mn alloys: Mossbauer spectroscopy observation(Springer, 2005) Aktürk, S.; Durlu, Tahsin Nuri…Öğe New observations on the formation of athermal martensite in Fe-Ni-Mo alloys(Elsevier Science Sa, 2007) Yasar, Eyüp; Güngüneş, Hakan; Aktürk, S.; Durlu, Tahsin NuriThe thermally induced gamma-epsilon and gamma-alpha' martensitic transformation in Fe-30%Ni-x%Mo alloys with different Mo contents have been studied by transmission electron microscopy (TEM). Observations reveal that alpha' martensite is found in alloys containing 0.8, 1.8, and 2.6% Mo, and 8 martensite in the alloy containing 5%Mo. The first three display the Kurdjumov-Sachs (K-S) orientation relationship between gamma and alpha', while the other displays the Shoji-Nishiyama (S-N) orientation relationship between gamma and epsilon. (c) 2006 Elsevier B.V. All rights reserved.Öğe Vickers microhardness studies of Fe-Mn binary alloys(Elsevier Science Bv, 2004) Bektes, M.; Uzun, O.; Aktürk, S.; Ekinci, A.E.; Uçar, N.The room temperature microhardness of Fe-Mn binary alloys with different compositions was measured using a Vickers microhardness tester in the applied load ranging from 0.245 to 4.9 N. A significant indentation size effect was observed for each sample at low indentation test loads. The classical Meyer's law and proportional specimen resistance model were used to analyze the microhardness behaviour. It was found that the Fe-Mn binary alloys become harder with increasing Mn composition and this can be attributed to solid-solution hardening.
