EFFECT OF AGING UNDER COMPRESSIVE STRESS ALONG [100] IN Co–Ni–Ga SINGLE CRYSTALS

2009 ◽  
Vol 02 (02) ◽  
pp. 83-86 ◽  
Author(s):  
C. PICORNELL ◽  
J. PONS ◽  
E. CESARI ◽  
Y. I. CHUMLYAKOV ◽  
J. DUTKIEWICZ
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory ◽  
Critical Stress ◽  
Parent Phase ◽  
Ferromagnetic Shape Memory Alloy ◽  
Slow Recovery ◽  
Transformation Temperatures ◽  
Two Stages ◽  
Ferromagnetic Shape Memory ◽  
Pseudoelastic Behavior

The pseudoelastic behavior of a Co 49 Ni 21 Ga 30 ferromagnetic shape memory alloy under compression along [100] has been studied in the temperature range 300–500 K. In such a crystals, the effect of aging under a constant stress close to the critical stress to induce the martensitic transformation, produces its separation in two stages. This is due to the different ordering behavior of parent and martensite phases under aging. Increasing order of parent phase leads to a decrease of transformation temperatures, which in return leads to an increase in critical stress to induce the transformation. Aging of martensite produces its stabilization — increase in transformation temperatures. It is remarkable that this stabilization has a very slow recovery, as compared to other alloys systems, such as Cu-based shape memory alloys.

TEM Study of Ni-Mn-Co-In Ferromagnetic Shape Memory Alloys

2012 ◽  
Vol 186 ◽  
pp. 271-274
Author(s):  
Krystian Prusik ◽  
Katarzyna Bałdys ◽  
Danuta Stróż
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Parent Phase ◽  
Cobalt Content ◽  
Indium Content ◽  
Ferromagnetic Shape Memory Alloys ◽  
Transformation Temperatures ◽  
Ferromagnetic Shape Memory

Ferromagnetic shape memory alloys (FSMA) are relatively new smart materials group. Recently, new FSMA from NiMnX (X=Sb, Sn, In, Co+In) systems are considered as alternative to the well known NiMnGa alloys. Four alloys of the following compositions: Ni43Mn35Co4In18, Ni41Mn35Co4In20, Ni42Mn35Co5In18, Ni40Mn35Co5In20 were studied in order to determine microstructure, phase composition and martensitic transformation temperatures versus their chemical composition. Structure of the alloys was studied by optical and transmission electron microscopy (TEM). All of the studied alloys showed macrostructure consisting of radially oriented columnar grains in the direction perpendicular to the casting axis. The structure of the phases occurred in the studied alloys depended on the cobalt and indium content. For the alloys containing 20 at. % of In at room temperature only L21 parent phase was observed whereas for those containing 18 at. % of In either single phase 14M modulated martensite or mixture of 14M martensite and L21 parent phase were seen. DSC measurements showed in studied alloys single-state martensitic transformation. Decrease In content of 2 at.% caused about 80°C fall of martensitic transformation temperatures. Curie temperature Tc increases of 20°C with 1 at% rise of the cobalt content.

Effect of L21 Ordering on the Martensitic and Intermartensitic Transformations in a Ni-Mn-Ga Shape Memory Alloy

2007 ◽  
Vol 130 ◽  
pp. 127-134
Author(s):  
Concepcio Seguí ◽  
Jaume Pons ◽  
Eduard Cesari
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Single Crystal ◽  
Shape Memory ◽  
Parent Phase ◽  
Heat Treatments ◽  
Free Energies ◽  
Transformation Temperatures ◽  
Reverse Martensitic Transformation ◽  
Order Degree

The present work analyses the influence of austenite ordering on a single crystal Ni-Mn- Ga alloy which displays, on cooling, a sequence of martensitic (MT) and intermartensitic (IMT) transformations. The MT and IMT show distinct behaviour after ageing in austenite: while the MT temperatures are not affected by the performed heat treatments, the IMT shifts toward lower temperatures after quenching from increasing temperatures, progressive recovery occurring upon ageing in parent phase. Such evolution can be related to changes in the L21 order degree, in the sense that ordering favours the occurrence of the intermartensitic transformation, while it does not affect noticeably the forward and reverse martensitic transformation temperatures. The closeness of the free energies of the different martensite structures allows to explain this behaviour.

Martensitic Transformation and Shape Memory Effect of Ni53.25Mn21.75Ga25 Ferromagnetic Shape Memory Alloy

2012 ◽  
Vol 476-478 ◽  
pp. 1504-1507
Author(s):  
Hai Bo Wang ◽  
Shang Shen Feng ◽  
Pei Yang Cai ◽  
Yan Qiu Huo
Keyword(s):  
Magnetic Field ◽  
Martensitic Transformation ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Parent Phase ◽  
Transformation Strain ◽  
Scanning Calorimetry ◽  
Reversible Transformation ◽  
Ferromagnetic Shape Memory

The martensitic transformation, crystalline structure, microstructure and shape memory effect of the Ni53.25Mn21.75Ga25 (at.%) alloy are investigated by means of Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and the standard metal strain gauge technique. The XRD results showed that the Ni53.25Mn21.75Ga25 alloy is composed of cubic parent phase at room temperature. TEM observation proved that the typical twin martensite is tetragonal structure and tweed-like contrast which is typical image for the parent phase. A large reversible transformation strain, about 0.54%, is obtained in this undeformed polycrystalline alloy due to martensitic transformation and its reverse transformation. This transformation strain is also increased to 0.65% by the external magnetic field. It is believed that the effect of the magnetic field on the preferential orientation of martensitic variants increases the transformation strain.

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