This study analyzes the influences of Zr addition on the martensitic transformation behavior, microstructural evolution, mechanical properties and superelasticity effect of arc-melted Ti-12V-4Al-xZr (x = 0, 0.5, 1, 1.5 and 2 wt.%) high temperature shape memory alloys (HTSMA). The results revealed that the austenite transformation temperatures and activation energy values decreased linearly when the Zr addition was greater than 0.5 wt.%. The Ti-V-4Al (wt.%) and Ti12V-4Al-0.5Zr (wt.%) alloys were composed of α″ martensitic phase, while the others consisted of predominant α″ martensitic phase and a small amount of the β austenite phase. The thickness of martensitic plates in the alloys reduced with increased Zr addition. Hardness and reduced elastic modulus values calculated from load-depth curves of the alloys also decreased with increasing Zr addition. Along with the increase in the Zr addition, the alloys’ superelasticity behavior decreased at room temperature (24 °C), while this behavior increased at the high temperatures (450 °C).
In this work, YBa2-xCsxCu3O7-δ (x= 0.05, 0.1, 0.2 and 0.3 wt. %) samples were prepared by using solid state reaction method. Some electrical, physical and structural properties of these compounds were examined by using SEM (scanning electron microscopy), XRD (X-ray diffraction), electrical resistivity, critical current density and AC susceptibility measurements, respectively. On the basis of the SEM measurements, it would seem that increasing the amount of Cs doping, the porous structures decrease and the grain size increases up to approximately 50 μm. Unit cell parameters were calculated by employing XRD measurements. On the basis of the data obtained from X-ray diffraction, Cs atoms displaced Ba atoms in the crystal structure. From the measurements of electrical resistivity at 80 K-120 K temperature, it was determined that the highest transition temperature was 91.5 K after addition of 0.05 wt. % Cs. The critical transition temperature was decreased by increasing the amount of Cs doping. Critical current density measurements on the same samples showed that as the amount of Cs doping increases, the values of Jc decrease. AC magnetic susceptibility measurements showed a sharper transition to the superconducting state in YBa2-xCsxCu3O7-δ (x= 0.05, 0.1, 0.2 and 0.3 wt.%) samples with the increase in the additive amount.
In this study, the effects of Zr addition on phase transformation temperatures, microstructure of Ti-12V-4Al (wt. %) high temperature shape memory alloys (HTSMAs) manufactured using melt-spinning technique were investigated. During heating, differential scanning calorimetry (DSC) curves showed that austenite transformation temperature of Ti-12V-4Al (wt. %) meltspun ribbon was single-stage transformation and Ti-12V-4Al-0.5Zr (wt. %) melt-spun ribbon was two-stage transformation. In the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyzes, unveiled that the melt-spun ribbons consisted of martensite, austenite and R phases. Transmission electron microscopy (TEM) analysis showed that the thickness of martensite plates in ribbons was thinned by the addition of Zr.
High temperature shape memory alloys (HTSMAs) are widely used in many fiels such as industry, biomedical, aerospace, etc. In order to expand the usage areas of these alloys, it is necessary to improve the materials, especially the martensitic transformation temperatures should be controlled. Third elements are often added to the material to control the martensitic transformation temperature. Ti-12V-8Al (wt. %) alloy, which is prepared for use in aircraft engines in the aviation industry, is a good choice due to its low density. In this study, Ti-12V-8Al (wt. %) alloy was prepared with the help of arc-melting technique. The martensite-austenite transformation temperatures, phase formations, microstructure of Ti-12V-8Al (wt. %) alloy were examined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM) respectively. In the DSC test, it was determined that the martensitic transformation temperature reduced according as the heating rate of the alloy. In XRD and SEM measurements, it was observed that the alloy has α″ martensitic phases as well as some β austenite phases. Thermal activation energies of the alloy were founded by Kissinger and Ozawa techniques. It was concluded that the activation energy amounts computed by these two techniques are parallel to each other.
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