Phase transformation temperatures and physical characteristics of NiTiCo shape memory alloys produced by arc melting met
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Phase transformation temperatures and physical characteristics of NiTiCo shape memory alloys produced by arc melting method Cengiz Tatara , Murat Kurt Faculty of Science, Department of Physics, Firat University, Elazig, Turkey Received: 14 April 2020 / Accepted: 31 August 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The effect of cobalt addition with different proportions into Ni50−x Ti50 Cox x 2, 4, and 6 wt%) shape memory alloys was investigated. The alloys were produced by arc melting method and then some characteristics, including microstructure, phase transformation temperatures, and magnetic properties, were analyzed. Additionally, the determination of the crystal structure on the alloy’s microstructural phases, changes in chemical composition proportions, phase transformation temperatures, and magnetization were investigated at room temperature using XRD, SEM–EDX, DSC, and PPMS, respectively. As a consequence of these measurements, the absorbed and released energies and transformation temperatures exhibit an obvious decrease with the increase of Co addition into the alloys. The microhardness results revealed that the second phase of the alloys has higher hardness compared to the matrix phase. Moreover, with the increase of Co addition into the alloy, Gibbs free energy showed a regular increase while elastic energy exhibited irregular changes. The increase of Co addition to the alloys increased the magnetization property of the alloys.
1 Introduction Martensite transformation is a first-order diffusionless structural phase transformation between a high-temperature austenite phase and a low-temperature martensite phase [1–3]. Thermoelastic martensite transformations are diffusionless crystal structural changes that proceed with the shear motion of crystallographic planes at the transformation interface. Furthermore, thermoelastic martensite transformation is both a mechanical process and a thermal transformation process. Owing to this unique combination, specific thermodynamic conditions have been established to express the effects of stress and temperature, as the external driving forces, in the transformation. One of the most important and applicable groups of alloys that belongs to the functional materials is the shape memory alloys (SMAs), which have attracted much attention because of their superior characteristics, good mechanical properties, and superb corrosion resistance. Among available SMAs, near-equiatomic NiTi alloy is regarded as the most workable and useful alloy because of its superelasticity (SE) coupled with the shape memory effect (SME) [4–8]. One limitation of NiTi SMA is the maximum martensite transformation temperature
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(100 °C); however, it can be elevated by adding a third element such as Pt, Au, Pd, Hf, Zr and Co with sufficient amount [9–13]. Adding a third element or a slight change i
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