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Öğe THE EFFECT OF CHROMIUM ADDITION ON PHYSICAL PROPERTIES OF Cu-Al BASED HIGH TEMPERATURE SHAPE MEMORY ALLOY(Polska Akad Nauk, Polish Acad Sciences, Inst Metall & Mater Sci Pas, 2018) Cirak, Z. Deniz; Kok, M.; Aydogdu, Y.Cu-Al-based high temperature shape memory alloys are preferred commonly due to their cheap costs and shape memory properties. In recent years, studies have been conducted on developing and producing a new type of Cu-Al based shape memory alloy. In this study, the CuAl-Cr alloy system, which has never been produced before, is investigated. After production, the SEMEDX measurements were made in order to determine the phases in the Cu84-xAl12Crx+4 (x = 0, 4, 6) (weight %) alloy system; and precipitate phases together with martensite phases were detected in the alloys. The confirmations of these phases were made via x-ray measurements. The same phases were observed by XRD diffractogram of the alloys as well. The values of transformation temperature of alloys were determined with Differential Scanning Calorimetry (DSC) at 20 degrees C/min heating rate. According to the DSC results, the transformation temperature of the alloys varies between 320 degrees C and 350 degrees C. This reveals that the alloys show high temperature shape memory characteristics.Öğe The effect of Sn content on mechanical, magnetization and shape memory behavior in NiMnSn alloys(Elsevier Science Sa, 2016) Aydogdu, Y.; Turabi, A. S.; Kok, M.; Aydogdu, A.; Yakinci, Z. D.; Aksan, M. A.; Yakinci, M. E.The effects of the composition alteration on the magnetization and shape memory behavior of Ni50Mn40-xSn10+x (x = 0, 1, 2, 3) alloys were systematically investigated by thermal, magnetic and mechanical experiments. Phase transformation from ferromagnetic austenite to weakly magnetic martensite was observed during thermal cycling under magnetic field and transformation temperatures were decreased with increasing Sn (or decreasing Mn). Moreover, the saturation magnetization of martensite increased with Sn content. Ni50Mn40Sn10 showed the recoverable strain of 2.1% during thermal cycling under 300 MPa and the reversible superelastic strain of 2% at 190 degrees C. Mechanical experiments exhibited that the largest compressive deformation of about 7% at 650 MPa occurred in Ni50Mn39Sn11 while Ni50Mn40Sn10 had fractured at 4% and 390 MPa at room temperature. (C) 2016 Elsevier B.V. All rights reserved.Öğe The effects of boron addition on the magnetic and mechanical properties of NiMnSn shape memory alloys(Springer, 2016) Aydogdu, Y.; Turabi, A. S.; Aydogdu, A.; Kok, M.; Yakinci, Z. D.; Karaca, H. E.The effects of boron addition on the microstructure, magnetic, mechanical, and shape memory properties of Ni50Mn40-xSn10Bx (at.%) (x = 1, 2, 3, 4, 6, 8) polycrystalline alloys were systematically investigated. It was revealed that transformation temperatures, magnetic behavior, mechanical, and shape memory properties can be tailored by B content. Transformation temperatures were decreased while saturation magnetization was increased with the addition of boron. In addition to magnetic behavior, ferromagnetic austenite transforms to weakly magnetic martensite, and then, martensite becomes ferromagnetic during cooling. The low amount of B addition (up to 4 %) to NiMnSn creates the second phase which provides higher strength and ductility. However, the high volume fraction of the second phase reduces the shape recovery because the phase transformation does not occur in the second phase. Brittleness takes place when the B amount is more than 6 % in NiMnSnB alloys. The amount of boron content in the NiMnSnB alloys plays a significant role to modify the magnetic, mechanical, and shape memory properties.Öğe Effects of In-situ and Ex-situ Heat-Treatment Procedures on the Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System(Springer, 2011) Yakinci, M. E.; Aydogdu, Y.; Aksan, M. A.; Balci, Y.; Altin, S.Superconducting MgB2 thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 mu m thick MgB2 films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T (c) and T (zero) of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12x10(6) A cm(-2) for ex-situ annealed films and 4.01x10(6) A cm(-2) for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.Öğe The effects of substituting B for Cu on the magnetic and shape memory properties of CuAlMnB alloys(Springer Heidelberg, 2016) Aydogdu, Y.; Turabi, A. S.; Aydogdu, A.; Vance, E. D.; Kok, M.; Kirat, G.; Karaca, H. E.The effects of B addition on the magnetization, mechanical and shape memory properties in Cu70-xAl24-Mn6Bx at.% (x = 0, 1, 2, 3, 4) alloys have been investigated. The ductility was decreased, while the strength was improved with B addition. Transformation temperatures were increased with B content due to increased e/a ratio. Martensite start temperature of B-free CuAlMn was found to be 37.3 degrees C and increased to 218.8 degrees C with 4 % B addition. B-free CuAlMn exhibited shape memory effect with a recoverable strain of 2.25 % under 200 MPa and a perfect superelasticity with a recoverable strain of 2.5 % at 163 degrees C. B addition degraded the shape memory properties and eventually resulted in the lack of recoverable strain. In addition, saturation magnetization was increased with B content. Moreover, the addition of B slightly decreased the ductility of the alloy. It was found that the magnetization, mechanical and shape memory properties CuAlMn alloys can be tailored by quaternary alloying with B.Öğe Electrical and optical properties of ZnO-Fe2O3-SiO2 composite prepared by SOL-GEL method(Amer Inst Physics, 2007) Canbay, C. Aksu; Altin, S.; Aydogdu, A.; Aydogdu, Y.; Yakinci, E.The semiconductor composite was prepared from ZnO, Fe2O3 and SiO2 transition metal oxides by sol-gel method. The surface morphology of the prepared samples were investigated by scanning electron microscopy (SEM). The activation energies of the samples in the extrinsic and intrinsic regions were found as 0.75 eV and 0.77 eV for ZFS-1 and 0.22 eV and 0.32eV for ZFS-2. The value of the optical band gap of the composite samples were calculated from the absorption coefficient depending on photon energy. The optical band gap of the samples were found as 1.60 eV and 1.70 eV for ZFS-1 and ZFS-2, respectively.Öğe Magnetic field induced martensitic transition in Fe doped Ni-Mn-Sn-B shape memory ribbons(Elsevier Sci Ltd, 2019) Kirat, G.; Aksan, M. A.; Aydogdu, Y.In this study, effect of the Fe-doping on the microstructural evolution, phase transformation and magnetoresistance properties of the Ni-Mn-Sn-B magnetic shape memory ribbons fabricated by melt-spinning technique were investigated. While the phase transition temperatures from austenite to martensite in the undoped ribbon was very close to room temperature, it was found that they decreased by the Fe-doping, which was attributed to decrease in the e/a value with the Fe-content. A voltage change of 5 mu V at a constant current of 1 mA and at 283 K and in the magnetic range of 0-10 kOe was obtained, which is good value obtained for the Heusler alloys. The resistivity data measured in the martensitic - austenite transition region was overlapped at similar to 90 kOe, which is clear evidence for the magnetic field-induced one way martensitic transition. The ribbons showed an antiferromagnetic behavior at low magnetic field and a ferromagnetic behavior at high magnetic fields. The Fe-doping to the Ni-Mn-Sn system caused a significant increase in the magnitude of the magnetization. The results showed that the melt-spinning technique used in the production of magnetic shape memory strips is very promising for magnetic sensor applications.Öğe Nano-sized Spherical MgB2 Superconducting Powder Fabrication Using MHz Range Ultrasonic Spray Pyrolysis (USP) System(Springer, 2011) Yakinci, M. E.; Aksan, M. A.; Balci, Y.; Altin, S.; Onal, Y.; Aydogdu, Y.We have fabricated 40-150 nm sized MgB2 superconducting spherical powders by using a 2.4 MHz ultrasonic spray pyrolysis system and consecutive high temperature heating and powder collection chamber. Various chemical solutions, which contain Mg, B, de-ionized water, acetone and LAPSA in different concentrations and gas atmosphere, were used to obtain MgB2 superconducting powders. Microstructural, transport and magnetic characterizations of the powders were performed using XRD, SEM-EDX, R-T, M-H analysis and critical current density calculations, which is found in the range of 10(6) Acm(-2), indicating improved flux pinning properties.Öğe Synthesis and Characterization of MgB2 Thin Films Prepared by 2.4 Mhz Ultrasonic Spray Pyrolysis System(Springer, 2011) Yakinci, Z. D.; Aydogdu, Y.Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al2O3(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB2 superconductors. After an in-situ heating process, similar to 600-1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM-EDX, R-T, and M-H analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB2 films were discussed. The best T (c) and T (zero) results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al2O3(001) substrates. Magnetic properties of the MgB2 films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum J(c)(mag) value was calculated to be 4.0x10(6) A cm(-2) at 10 K for 0 T for the film deposited on the Al2O3(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.Öğe Thermal and magnetic properties of Ni51Mn28.5Ga19.5B magnetic-shape-memory alloy(Springer, 2014) Kok, M.; Yakinci, Z. D.; Aydogdu, A.; Aydogdu, Y.Ni51Mn28.5Ga19.5B magnetic shape-memory alloy was produced in Arc melter under vacuum. The crystal structure of the produced alloy was determined by using XRD. The XRD analysis results indicated the presence of two phases; namely the martensitic phase that the alloy was determined to display non-modulated martensitic phase and the gamma phase characteristics. DSC was used to determine the transformation temperature, the thermodynamic quantities of martensitic transformation and the activation energy in the Ni51Mn28.5Ga19.5B alloy. The austenite transformation temperature and activation energy of transition were found as 46.92 A degrees C and 303.12 kJ mol(-1) respectively. The 1 % presence of the boron element in the alloy was observed to play a significant role in the transition temperature as indicated by the comparison of the values obtained in this study with those available in the literature. The magnetic properties of this alloy were determined using the PPMS instrument. The magnetic saturation value was determined as 66 emu g(-1).Öğe Thermoelectric and mechanical properties of Mg-Al-Sb alloys(Springer, 2015) Altin, E.; Oz, E.; Erdem, M.; Demirel, S.; Aydogdu, Y.; Altin, S.We fabricated Mg-Al-Sb alloy by arc melting system. Microstructural analyses were performed and it was found that only Mg3Sb2 and AlSb phases formed for different heat treatment conditions. The phase transition at 580 degrees C according to DTA analysis was determined as partial melting and it was supported by phase analyses studies in the literature. The resistivity results showed the metallic and the semiconducting type behavior depending on the heat treatment temperatures. The thermal conductivity measurement was performed in the range of 2-300 K and the data were analyzed by the sum of lattice and carrier components. The thermopower data showed negative and positive values which indicate the sign of total carriers. The linear temperature dependence of thermopower indicates metallic type characteristic of the samples. Mechanical properties of the sample showed two type hardness values dependent on heat treatment temperature.Öğe Thickness Dependence of Critical Current Density in MgB2 Films Prepared by Thermal Evaporation Method(Springer, 2011) Yakinci, Z. D.; Aydogdu, Y.MgB2 films with the thickness of 350 to 1150 nm have been prepared on the Al2O3 (001) single crystal substrates from high purity B and Mg powder by the thermal evaporation method. Films were then heat treated ex-situ under Mg vapor at 950 A degrees C to achieve actual MgB2 stoichiometry. Thickness of the films, so the deposition time, was varied to investigate its influence on critical current density of the films. The films fabricated were analyzed by means of microstructural, transport, and magnetic properties. The best T (c) and T (zero) values were obtained to be 39.5 K and 38 K, respectively, and decreased with increasing the thickness. We found that the critical current density of the films prepared is highly thickness dependent. The maximum J(c)(mag) value was calculated to be 3.18x10(6) A cm(-2) at 10 K and zero field for 1150 nm thick films but dropped drastically by thickness.
