Browsing by Author "Seyedmohammadi, Seyedveghar"

Now showing 1 - 6 of 6

Metadata only
Addressing the strength-ductility trade-off in a thermomechanical-processed high entropy alloy
(Elsevier, 2023-12-15) Radi, Amin; Işıl, Canay; Seyedmohammadi, Seyedveghar; Kim, H. S.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Işıl, Canay; Seyedmohammadi, Seyedveghar
High entropy alloys (HEAs) have garnered significant attention due to their exceptional mechanical behavior. However, the influence of secondary phases and dislocation substructures has yet to be thoroughly investigated. This study focuses on the incorporation of the decomposed η-phase within a face-centered cubic (FCC) microstructure at different recrystallization levels, aiming to achieve adequate ductility while maintaining strength at gigapascal levels. Various characterization techniques were employed to analyze the microstructure of both homogenized and annealed+aged conditions. Implementing a sub-micron grain size distribution and introducing a favorable dislocation substructure significantly enhanced the mechanical properties of yield strength, ultimate tensile strength, and ductility, reaching up to 1291 MPa, 1450 MPa, and 17.5%, respectively. The results highlight the influential role of grain size in facilitating the generation of geometrically necessary dislocations during plastic deformation.
Metadata only
Effect of a multi-phase structure on the damping response of a novel high entropy alloy
(Elsevier, 2022-12-01) Işıl, Canay; Radi, Amin; Seyedmohammadi, Seyedveghar; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Işıl, Canay; Radi, Amin
In this study, dynamic behavior of a novel multi-phase high entropy alloy (HEA) was investigated. Thermo-mechanical processes containing an 80 % thickness reduction at room temperature rolling followed by annealing at 750 °C and 850 °C were applied to modify the microstructure and the resulting damping properties of the HEA. Annealing at 750 °C introduced the BCC phase, while at 850 °C, the sigma phase was prevalent in the microstructure, leading to over 1 GPa strength with decent ductility in the latter condition. The storage modulus and the internal friction values of the annealed alloys are noticeably improved, indicating that application of suitable heat treatments could enhance both the mechanical response and the damping performance of this HEA.
Metadata only
Effect of processing parameters on the phase transformation of a high temperature copper-based shape memory alloy
(Springer, 2023-11) Seyedmohammadi, Seyedveghar; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Seyedmohammadi, Seyedveghar
In the present study, the influence of the processing parameters on the transformation temperatures and microstructural evolution in a copper-based shape memory alloy was investigated. Five times remelting in identical conditions was conducted to investigate the effect of successive remelting on the microstructural and thermal behavior of the alloy. Samples were hot rolled up to 25, 50, 75, and 90% reduction in thickness after heating at 900 °C. It was demonstrated that one-time remelting is required to achieve a target alloy composition. Thermal hysteresis remained almost constant with elevation in the rolling strain imposed. Furthermore, increased rolling reduction led to decreased enthalpy and entropy levels.
Metadata only
Effects of aging on the microstructure and phase transformation behavior of cu-al-mn shape memory alloy
(Trans Tech Publications Ltd, 2021) Seyedmohammadi, Seyedveghar; Radi, Amin; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Seyedmohammadi, Seyedveghar; Radi, Amin
In the present study, the effects of artificial aging heat treatment on the transformation temperatures and hardness of Cu-Al-Mn shape memory alloy have been investigated. The aging processes have been performed on the one-time re-melted and 90% rolled samples. Differential scanning calorimetry reveals that reverse transformation is present for the re-melted sample which is aged at 400°C. However, in 90% rolled condition, this transformation takes place at 200°C and 300°C. Hardness examination shows that the aged specimens possess higher values in hardness in comparison to un-aged samples at all studied temperatures. Although, the peak-aged condition was demonstrated at 300°C for the re-melted sample, the rolled sample displayed increased hardness levels up to 500o C. Based on the DSC measurements and microstructural observations, it can be asserted that the thermo-mechanical processing including rolling plus aging at 300o C provides favorable transformation characteristics for shape memory behavior.
Metadata only
On the low-cycle fatigue behavior of a multi-phase high entropy alloy with enhanced plasticity
(Elsevier, 2023-08) Radi, Amin; Sajadifar, S.; Seyedmohammadi, Seyedveghar; Krochmal, M.; Bolender, A.; Wegener, T.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Seyedmohammadi, Seyedveghar
A multi-phase non-equiatomic FeCrNiMnCo high entropy alloy (HEA) was fabricated using vacuum induction melting. Thermo-mechanical treatments consisting of cold rolling and annealing at 750 °C and 850 °C were employed to improve the mechanical properties of the HEA in focus. Tensile experiments revealed that yield strength and ultimate tensile strength levels can be enhanced significantly after thermo-mechanical processing (TMP). At the same time, ductility remains at an adequate level. Strain-controlled low-cycle fatigue (LCF) experiments were carried out in order to assess the mechanical properties of this HEA under cyclic loading conditions. At the same strain amplitude, the stress levels of the processed samples were considerably higher than that of the as-received counterpart. Similarly, fatigue lives of the former could surpass the base condition at the strain amplitudes of 0.2% and 0.4%; however, at the higher strain amplitudes, cyclic softening was observed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) results revealed that phase transformation from face-centered cubic (FCC) to body-centered cubic (BCC/B2) took place at a higher occurrence with increasing strain amplitude (0.2% to 0.6%). Furthermore, transmission electron microscopy (TEM) studies confirm that upon tensile deformation additional plasticity mechanisms, i.e., deformation twinning and phase transformation, contribute to the overall mechanical behavior of the multi-phase HEA.
Metadata only
Thermo-mechanical processing and phase transformation behavior of Cu-Al-Mn shape memory alloy
(2021-08-18) Seyedmohammadi, Seyedveghar; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Başol, Altuğ Melik; İpekoğlu, M.; Department of Mechanical Engineering; Seyedmohammadi, Seyedveghar
Thermo-mechanical Processing And Phasetransformation Behavior Of Cu-al-mn Shape Memory Alloy. Cu-Al-Mn shape memory alloys have attracted noticeable interest between copper-based SMAs, due to the high ductility and wide transformation temperature range. Furthermore, because of the unique mechanical and thermal properties, these alloys have extensive applications in industries which is comparable to NiTi-based SMAs. The alloying composition, production methods, and heat treatment conditions are the effective parameters on the phase transformation temperatures and mechanical properties. In the current thesis, the Cu86Al12Mn2 wt.% was manufactured by conducting an induction melting method under vacuum. The phase transformation temperatures and microstructure development were examined by considering the different re-melting times, rolling, and heat treatment conditions. Based on the literature, the re-melting process is necessary to achieve a homogeneous alloy after the casting process, however, there is a lack of information related to the effect of numbers of re-melting on both microstructure and mechanical properties of these alloys. Therefore, the re-melting process in the conditions same as initial casting was subjected to obtain the effective re-melting time for achieving a homogeneous alloy. It was found that one-time re-melting is required and enough to achieve a homogeneous alloy. The thermal analysis test results for all re-melted samples demonstrated stabilization of transformation temperatures after the re-melting process. In order to investigate the influence of plastic deformation on thermal and mechanical behavior, the rolling process on one-time re-melted samples was done in different rolling conditions. A hot rolling process at 900°C was considered based on the calculation of workability for current alloy. Grain refinement was observed with increasing the thickness reduction during the rolling process from 25% to 90%, which subsequently increased the transformation temperatures as well. Studying re-melt and plastic deformation is not the only aim of this research work. Another important aspect is the aging heat treatment. Thus, the aging responses of 25% and 90% rolled samples were investigated at 300°C and 400°C with various durations. It was found that after aging at 400°C for more than 60 minutes, γ' precipitates were produced in the sample. Also, by increasing the aging time to 480 minutes at 400°C, vast distribution of coarse γ' precipitates was observed. Moreover, the differential scanning calorimetry (DSC) results of the 90% rolled sample which was aged at 400°C for 480 minutes illustrated the loss of shape memory effect. Last but not least, the impact of thermo-mechanical processing on the superelasticity and shape memory properties of Cu-Al-Mn alloy was also explored. The shape memory effect was evaluated by the bending test, and the response was about 90% strain recovery in rolled samples. However, the aged samples illustrate about 50% strain recovery. No superelasticity behavior (SE) was observed over Af temperature. As a summary, the effects of casting parameters and aging conditions on the phase transformation temperature and mechanical behavior of Cu-Al-Mn alloy were investigated. It was found that one-time re-melt with vacuum induction melting (VIM) method and hot rolling followed by a solutionizing process is required to manufacture the SMA. Aging over Af temperature showed an increase in hardness value to 320 Hv, and loss of shape memory effect. These findings are caused by the generation of the γ' precipitates after 480 minutes of aging at 400°C.