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Atomic Ordering Behavior of CoTi Alloy with Addition of Transition Metals

Hussain Abid, Ziya Amer Bashir, Atiq Shabbar, Saleem Muhammad, Ullah Mahtab, Ahmad Sajjad, Ahmad Naseeb

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 2

425--430

The statistical-thermodynamic theory of ordering and electronic theory of ordering in the pseudo-potential approximation was used to study the influence of ternary addition of some transition metals on the atomic ordering behavior of Co0.5(Ti1-xMx)0.5 alloys with M = Fe, Pt, re, V, Cr, Mn, Ni, Cu, Zn, Zr, Ag, Hf or Au up to a concentration of 1 at.%. The partial ordering energies, order-disorder phase transformation temperatures and partial short range order parameters have been calculated for these alloys. The analysis shows that the impurity elements in Co0.5(Ti1-xMx)0.5 alloys can be divided into two main groups on the basis of lattice site occupancy i.e. M = V, Cr, Mn, Cu, Zn, Zr, Ag, Hf and Au mainly substitute for Co sublattice sites whereas M = Fe, Ni, Pt or re mainly substitute for Ti sublattice sites. Further, the order-disorder transformation temperatures were found to either increase or remain nearly unchanged by the addition of ternary impurities in the CoTi alloy depending on the absolute value of the partial ordering energies. Alloys of Ti with V, Cr, mn, Cu, Zn, Zr, Ag, Hf or Au in place of Co and alloys of Co with Fe, Ni, Pt or Re in place of Ti can be predicted for future. The results of the present analysis are in good agreement with the available experimental data on these alloys.

Prestress state evolution during thermal activation of memory effect in concrete beams strengthened with external SMA wires

Debska A., Gwozdziewicz Piotr, Seruga A., Balandraud X., Destrebecq J. F.

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 4

659--673

The memory effect of shape-memory alloys (SMAs) has opened interesting perspectives to create prestress states in concrete elements. However, the procedure has not been yet fully resolved due to the complex thermomechanical behavior of these alloys, in addition to the practical difficulties of mechanical coupling between SMA and concrete elements. The present study deals with tests on the development of prestressing forces in concrete beams during the thermal cycle required in the procedure. Pre-stretched nickel–titanium wires were externally placed on concrete prismatic beams equipped with strain gauges. As concrete rupture may occur during the heating by the Joule effect, a compromise must be found between the SMA pre-stretch level and the maximum temperature to be applied before returning to ambient temperature. A macroscopic model was developed to analyze this compromise. The complex thermomechanical response of SMAs implies a particular attention in the definition of the ambient temperature and heating conditions for the creation of prestress states in concrete components.

Effect of cold deformation to transformation temperatures of Ni-Ti shape memory alloys

Yildiz C., Kucukyildirim B. O., Akdogan Eker A.

Archives of Materials Science and Engineering

2014

Vol. 66, nr 1

37--44

Purpose: of this paper is to predict the effect of cold deformation to transformation temperatures of Ni–Ti SMA and clarify the relation between cold forming ratio and the parameters of thermo mechanical process. Design/methodology/approach: 25% and 50% cold formed Ni–Ti wire specimens are investigated for defining the relation between the ratio and the parameters of thermo mechanical processes of without annealing and with annealing at 450°C for 30 minutes and 600°C for 30 minutes. Moreover, Differential Scanning Calorimeter (DSC) measurements are applied to the specimens for obtaining the transformation temperatures. Findings: According to DSC measurements, start and finish temperatures of transformation of austenite, martensite and rhombohedral phases are calculated. Hence, their changes are related to deformation and annealing, so it can be implied that cold deformation process leads to increases in the temperature ranges, slow occurrences of transformation and also the shape memory property lowers. Research limitations/implications: It is observed that some specimens exhibit rhombohedral phase transformation and this affects the martensite phase transformation temperatures and results. Thus, annealing time can be increased to determine both positive and negative effect to transformation properties for further research. Moreover, the grainsize and form may also be effective, so this case should be studied. Practical implications: can be stated as suitable transformation temperatures must be paid attention to desired service temperatures of products those are made of Ni–Ti SMAs, otherwise they may exhibit unexpected shape change due to the affected transformation temperature. Originality/value: is that Ni–Ti SMAs may be exposed to cold deformation when they are manufactured for being given any product shape, so with this research it can be determined that if their transformation temperatures change or not. Besides, it can be implied that they change and so this study presents the changes, the intervals of start and finish temperatures relevant to the cold forming ratio.