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Öğe Effect of Mn content on the austenite-martensite phases and magnetic properties in Fe-Mn-Co alloys(Elsevier Science Sa, 2011) Sari, U.; Kirindi, T.The influence of the Mn content on the magnetic properties and microstructure of the Fe-Mn-Co alloys has been investigated by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Mossbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, epsilon (h.c.p.) and alpha' (b.c.c.) martensites, form in the as-quenched alloys. epsilon and alpha' martensites coexist in the Fe-Mn-Co alloys with 13.2-17.3 wt% Mn content while only epsilon martensite appears in the case of 20.7 wt% Mn. The amount of a' martensite decreases significantly while the amount oft martensite increases with an increase in Mn content. The lattice parameters of austenite increase also with increasing Mn content. In addition, Mossbauer spectra of the alloys reveal a paramagnetic character with a singlet for the gamma (f.c.c.) austenite and e martensite phases and a ferromagnetic character with a broad sextet for a' martensite phase. The magnetic character of the Fe-Mn-Co alloys changes as Mn content increases and the ferromagnetic character disappears completely in case of 20.7 wt% Mn. (C) 2011 Elsevier B.V. All rights reserved.Öğe Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy(Springer, 2011) Sari, U.; Kirindi, T.; Ozcan, F.; Dikici, M.The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, gamma(2), and alpha phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of gamma(2) phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into gamma(2) phase and equilibrium alpha phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, gamma(2), and alpha phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the gamma(2) phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.Öğe The effects of austenite phase deformation on microstructure and magnetic properties in Fe-13.4% Mn-5.2% Mo alloy(Springer, 2011) Kirindi, T.; Sari, U.The effects of austenite phase deformation on martensitic transformations and magnetic properties in Fe-13.4% Mn-5.2% Mo have been investigated by scanning electron microscopy, transmission electron microscopy, and Mossbauer Spectroscopy. The increase of plastic deformation rates on austenite phase created considerable changes in amounts of epsilon (h.c.p.) and alpha'(b.c.c.) martensite, and austenite grains size decreased. Analysis of microstructure and Mossbauer spectra show that the amount of e martensite increased at low deformation rates whereas it decreased at high deformation rate. Besides, Mossbauer spectra of the alloy reveal a ferromagnetic character with a broad sextet for alpha' martensite phase and a paramagnetic character with a singlet for the gamma (f.c.c.) austenite and epsilon martensite phases. In the other hand, the magnetic character of the alloy exhibits a different magnetic order depending on strain rates.Öğe Effects of deformation on microstructure and mechanical properties of a Cu-Al-Ni shape memory alloy(Elsevier Science Inc, 2008) Sari, U.; Kirindi, T.In Cu-11.92 wt.%Al-3.78 wt.%Ni shape memory alloy, the influence of deformation and thermal treatments on the microstructure and mechanical properties under the compression test were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Experiments show that the mechanical properties of the alloy can be enhanced by convenient heat treatments. The alloy exhibits good mechanical properties with high ultimate compression strength and ductility after annealing at high temperature. However, it exhibits brittle fracture and dramatic strain hardening, with linear stress-strain behavior after annealing at low temperature. The changes in the mechanical properties have been linked to the evolution of the degree of order, occurrence of precipitation, and variation of the grain size. From microstructural observations, it is seen that the beta(1)' (18R) and gamma(1)' (2H) martensite phases coexist at different fractions in the undeformed and deformed states. Deformation induces the changes between the beta(1)' and gamma(1)' martensites and deformation-induced martensites form at preferred orientations as mechanical twins. The beta(1)' martensite variants are twin-related with respect to the (128)(18R) mirror plane and a new orientation relationship for these twin variants is derived as (128)(A)parallel to (128)(C): [461](A)parallel to [461](C). Additionally, an increase in the amount of deformation causes martensite reorientation, de-twinning, and dislocation generation; also, the martensite plates are seen to have rearranged in the same orientation to be parallel with each other. (c) 2007 Elsevier Inc. All rights reserved.
