Alexei Sozinov
Helsinki University of Technology
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Featured researches published by Alexei Sozinov.
ieee international magnetics conference | 2000
Oleg Heczko; Alexei Sozinov; K. Ullakko
A room temperature extensional strain of 5.1% was observed in martensitic Ni/sub 48/Mn/sub 31/Ga/sub 21/ alloy in the magnetic field of 480 kA/m. The magnitude of field-induced strain decreases with increasing external compressive stress applied in the direction of expansion. The compressive stress of about 3 MPa prevents the development of the substantial field-induced strain. Magnetization curves obtained by VSM exhibit an abrupt magnetization change and a transient hysteresis in the first quadrant. Large reversible field-induced strain and the abrupt magnetization change are due to the rearrangement or redistribution of martensitic twin variants by the applied magnetic field. It was confirmed by optical observation of movement and nucleation of martensitic twin boundaries.
Journal of Applied Physics | 2004
Nataliya Lanska; Outi Söderberg; Alexei Sozinov; Yanling Ge; K. Ullakko; V.K. Lindroos
The crystal structure of ferromagnetic near-stoichiometric Ni2MnGa alloys with different compositions has been studied at ambient temperature. The studied alloys, with five-layered (5M) and seven-layered (7M) martensitic phases, exhibit the martensitic transformation temperature (TM) up to 353 K. Alloys with these crystal structures are the best candidates for magnetic-field-induced strain applications. The range of the average number of valence electrons per atom (e/a) was determined for phases 5M, 7M, and nonmodulated martensite. Furthermore, a correlation between the martensitic crystal structure, TM and e/a has been established. The lattice parameters ratio (c/a) as a function of e/a or TM has been obtained at ambient temperature for all martensitic phases. That the paramagnetic-ferromagnetic transition influences the structural phase transformation in the Ni–Mn–Ga system has been confirmed.
ieee international magnetics conference | 2002
Alexei Sozinov; A.A. Likhachev; K. Ullakko
Summary form only given. Magnetic shape memory materials are expected to have potential for a variety of actuating devices and sensors. Magnetic-field-induced rearrangement of the crystallographic domains (twin variants) can produce a large strain similar to a stress-induced one. We have found a giant magnetic field-induced strain approximately 10% at ambient temperature in a magnetic field less then 1 T in NiMnGa seven-layered martensitic phase. The strain is contributed by twin boundary motion which was confirmed by different experimental methods. From the analysis of X-ray diffraction data it was found that crystal structure of this phase is nearly orthorhombic having lattice parameters at ambient temperature a=0.619 nm, b=0.580 nm and c=0.553 nm (in cubic parent phase coordinates). The magnetic anisotropy properties of this phase were determined on the single-variant constrained samples using the magnetization curves M(H) recorded along [100], [010] and [001] directions. We demonstrate that low twinning stresses and a high level of magnetic anisotropy energy are the critical factors for the observation of a giant magnetic field induced strain.
Applied Physics Letters | 2010
Ladislav Straka; N. Lanska; K. Ullakko; Alexei Sozinov
Ni–Mn–Ga single crystals with a twinning stress of about 0.1 MPa were studied. They showed a tendency to stay in a single variant state and to retain only one or very few twin boundaries during martensite reorientation induced by an external stress or magnetic field. This makes the crystals problematic for application in a magnetic actuator. To solve the issue, we introduced many parallel twin boundaries into the crystals by bending. However, this twin microstructure was not stable under cycling load. Additionally, it exhibited a twinning stress of 0.8 MPa—about ten times higher than a crystal with a single boundary.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 1999
Valentin G. Gavriljuk; Hans Berns; C. Escher; N.I. Glavatskaya; Alexei Sozinov; Yu.N. Petrov
The effect of nitrogen and carbon on the strengthening of the austenitic steel Cr18Ni16Mn10 by grain boundaries is studied. It is established in accordance with previous results that, in contrast to carbon, nitrogen markedly increases the coefficient k in the Hall-Petch equation. Because of a pronounced planar slip induced by nitrogen and the absence of any noticeable segregation of nitrogen atoms at the grain boundaries, nitrogen austenite presents an excellent object for testing different existing models of grain boundary strengthening (pile-up of dislocations, grain boundary dislocation sources, work hardening). Based on the analysis of available data and measurements of interaction between nitrogen or carbon atoms and dislocations it is shown that the nitrogen effect can be attributed to a strong blocking of dislocation sources in grains adjacent to those where the slip started.
Encyclopedia of Materials: Science and Technology (Second Edition) | 2016
Ilkka Aaltio; Alexei Sozinov; Yanling Ge; K. Ullakko; V.K. Lindroos; Simo-Pekka Hannula
The magnetostrictive materials exhibit a strain caused by the orientation of the magnetic moment when exposed to a magnetic field. A particular class of magnetostrictive materials is called magnetic shape memory (MSM) alloys or ferromagnetic shape memory alloy (FSMA) materials, which can change their shape remarkably when subjected to magnetic field. In the following, the MSM materials are introduced and their extraordinary structure, properties, and performance are described.
Smart Structures and Materials 2003: Active Materials: Behavior and Mechanics | 2003
Alexei Sozinov; A.A. Likhachev; Nataliya Lanska; Outi Söderberg; K. Ullakko; V.K. Lindroos
Magnetic shape memory materials are expected to have a high potential in practical applications. Several ferromagnetic materials exhibiting the large magnetic-field-induced strain have been found in recent years. The largest field-induced strain is observed in Ni-Mn-Ga system. The most important experimental results on crystal structure, magnetic anisotropy and twinning stress of martensitic phases in Ni-Mn-Ga having tetragonal five-layered, orthorhombic seven-layered and tetragonal non-layered crystal structures are reported. Depending on the martensite crystal structure Ni-Mn-Ga alloys are able to show a really giant strain response (approximately 6% in tetragonal five-layered or 10% in orthorhombic seven-layered martensitic phase) in a magnetic field less than 1 T. Contrary to these two phases, a detectable field-induced strain is not observed in non-layered tetragonal martensitic phase in Ni-Mn-Ga system. Effect of crystal structure is in a good agreement with calculation of the magnetic-field-induced strain based on the model developed by authors. The effect of composition on appearance of undesirable non-layered tetragonal martensitic phase in Ni-Mn-Ga system is discussed based on the new experimental results.
Smart Structures and Materials 2001: Active Materials: Behavior and Mechanics | 2001
A.A. Likhachev; Alexei Sozinov; K. Ullakko
Present publication gives a detailed report about the experimental results obtained concerning the effect of external constant stress on the magnetic field controlled strain response during the cyclic change of the magnetic field. Simultaneously we represent a brief overview of the most important structural and magneto-mechanical properties of Ni48Mn30Ga22 - family magnetic shape memory alloys. We also discuss the physical mechanism of this effect using our last model developments.
Journal of Applied Physics | 2011
Ladislav Straka; Hannu Hänninen; N. Lanska; Alexei Sozinov
We demonstrate experimentally the existence of triple twins in Ni-Mn-Ga magnetic shape memory single crystals with a modulated five-layered martensite structure using optical observations andx-ray diffraction. Subsequently, we investigate the response of the crystals with triple-twin segments to compressive loading up to several MPa. Such loading typically resulted in an abrupt rearrangement of the twin microstructure to a configuration with many fine twins (1–10 µm in size) ending at a twin boundary. This type of twin microstructure exhibited recoverable deformation with up to 0.3% macroscopic strain and an estimated 2.5% local strain, while the recoverable strain was much smaller for other studied microstructure configurations. The results indicate that by the creation of a suitable twin microstructure, the originally pseudoplastic or magnetoplastic material can be made rubberlike elastic or magnetoelastic with the macroscopic recoverable strain comparable to 2.5%.
SPIE's 9th Annual International Symposium on Smart Structures and Materials | 2002
A.A. Likhachev; Alexei Sozinov; K. Ullakko
Present article briefly summarizes the mechanism of magnetic shape memory, main modeling principles and most important information about the main structural, magnetic and mechanical properties related to a family of non- stoichiometric Ni-Mn-Ga alloys. We also first consider in details the problems of energy balance, energy losses, optimization of work output and estimation of thermodynamic efficiency for Ni-Mn-Ga based MSMAs.