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1

Electronic structure and possible martensitic transformation in Ni2FeIn alloy

Gu Y., Xue F, Zhao G, Liu G., Liu Y., Li S.

Materials Science Poland

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2014

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Vol. 32, No. 3

396—401

EN

The electronic structure and magnetic properties of Heusler alloys (Ni2FeIn) have been studied by first principle calculations. The possible tetragonal martensitic transformation has been predicted and the structure optimization was made on cubic austenitic Ni2FeIn in Cu2MnAl type. The equilibrium lattice constant of austenitic Ni2FeIn is 6.03 A° . In tetragonal phase, the global energy minimum occurs at c=a = 1.29. The corresponding equilibrium lattice constants for martensite Ni2FeIn are a = b = 5.5393 °A and c = 7.1457 A° , respectively. In the austenitic phase, EF is located at the peak in the minority DOS for c=a = 0.96 to 1.20, but in the martensitic phase, EF moves to the bottom of the valley in the minority DOS, reducing the value of N(EF ) effectively. Both austenitic and martensitic phases are ferromagnetic and the Ni and Fe partial moments contribute mainly to the total moments. Therefore, the martensitic transformation behavior in Ni2FeIn is predicted.

2

Large Deformation Constitutive Theory for a Two-Phase Shape Memory Alloy

Panoskaltsis V., Polymenakos L. C., Soldatos D.

Engineering Transactions

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2014

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Vol. 62, iss. 4

355–-380

EN

In this work we examine significant theoretical issues related to the constitutive modelling of a two-phase shape memory alloy which undergoes large deformations. For this purpose, we propose a new generalized plasticity based model. The model is based on a standard fractions approach and considers a local multiplicative decomposition of the deformation gradient into elastic and inelastic (transformation induced) parts, as its basic kinematic assumption. We also assess the ability of the model in simulating several patterns of the complex behavior of the material in question, by three representative numerical examples. These examples comprise a standard uniaxial tension problem, a torsion problem and an additional problem dealing with non-conventional pseudoelastic response.

3

The effect of lattice distortion on the course of the martensitic transformations in NiTi shape memory alloys

Stróż D., Chrobak D.

Inżynieria Materiałowa

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2010

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Vol. 31, nr 3

272-275

EN

The analysis of the influence of precipitation processes as well as dislocation structure on the transformation course and its characteristic parameters in NiTi shape memory alloys was carried out in the work. In order to describe structural changes caused by thermo-mechanical treatment, transmission electron microscopy technique was applied; the study included in situ observations during cooling and heating the specimen in the microscope. The structural changes were related to the evolution of the martensitic transformation determined from the differential scanning calorimetry (DSC) measurements. It was found that the non-homogeneity of stress fields caused by presence of coherent precipitates or by specific dislocation structure results in a multi-stage martensitic transformation. The transformation is preceded by the R-phase transition. Also this transformation can occur in many stages. A thermodynamical model of the multi-stage martensitic transformations occurring in the two-component NiTi alloys was elaborated, which allows anticipation of the transformation sequences in these alloys.

PL

W pracy przeprowadzono analizę wpływu procesów wydzieleniowych oraz struktury dyslokacyjnej na przebieg przemiany martenzytycznej w stopach z pamięcią kształtu NiTi. W badaniach zastosowano technikę transmisyjnej mikroskopii elektronowej, w tym obserwacje podczas chłodzenia i grzania in situ w mikroskopie. Zmiany struktury powiązano z ewolucją przebiegu przemian wyznaczoną metodą różnicowej kalorymetrii skaningowej. Stwierdzono, że niejednorodność zniekształceń sieciowych, wywołanych obecnością w stopie koherentnych cząstek lub specyficzną strukturą dyslokacyjną, powoduje, iż przemiana martenzytyczna zachodzi wielostopniowo. Jest ona poprzedzona przemianą w fazę R. Także ta przemiana może zachodzić wielostopniowo. Opracowano termodynamiczny model wielostopniowej przemiany martenzytycznej, pozwalający przewidzieć sekwencje przemian w dwuskładnikowych stopach NiTi.