European Symposium on Martensitic Transformations

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Authors: Mikhail P. Kashchenko, Vera G. Chashchina
Abstract: Basic directions in the theory of martensitic transformations are briefly listed. Solutions of several important problems in the context of dynamic theory of reconstructive martensitic transformations are reviewed. The FCC-BCC (BCT) transformation in iron alloys is used as an example. Main attention is paid to concept links. In particular, the key role of the concept of initial exited state for realization of transformations with crystal growth at supersonic speed is shown. The leading value of this concept both for calculation of critical rates of austenite cooling and for estimation of scales of incubatory times at bainitic transformation is marked as well.
Authors: Michaël Peigney
Abstract: The peculiar properties of shape-memory alloys are the result of a solid/solid phase transformation between different crystallographic structures (austenite and martensite). This paper is concerned with the theoretical prediction of the set of strains that minimize the effective (or macroscopic) energy. Those strains, classically refered to as recoverable strains, play a central role in shape memory effect displayed by alloys such as NiTi or CuAlNi. They correspond to macroscopic strains that can be achieved in stress-free states. Adopting the framework of nonlinear elasticity, the theoretical prediction of stress-free strains amounts to find the austenite/martensite microstructures which minimize the global energy. Closed-form solutions to that problem have been obtained only in few special cases. This paper aims at complementing existing results on that problem, essentially by deriving bounds on the set of stress-free strains.
Authors: Georgiy Firstov, Andrei Timoshevski, Yuri Koval, Sergey Yablonovski, Jan Van Humbeeck
Abstract: This article is dedicated to the estimation of the relative stability for B2, B19`, B33 and Cm phase in ZrCu-ZrNi-ZrCo intermetallic compound row through the ab-initio electronic structure calculations and subsequent crystal structure Rietveld refinement. The information about electronic and crystal structure of phases in Zr-based intermetallics will allow selecting for this high temperature shape memory alloy such alloying elements that will significantly improve shape memory behavior through definite structural changes.
Authors: Vyacheslav Gundyrev, Vitaly Zel'dovich
Abstract: The criterion of an estimation of a reality of the mechanism of deformation of a lattice at martensite transformation is proposed. The most real mechanism of deformation of a lattice in FeNi alloy with the twinned martensite is determined. The Kurdjumov-Sachs shear on a plane (111) fcc in a direction [11-2] fcc is the basic component of deformation of a lattice in the given mechanism.
Authors: Hoang Anh Pham, Takuya Ohba, Shigekazu Morito, Taisuke Hayashi, Tadashi Furuhara, Goro Miyamoto
Abstract: The effect of titanium carbide (TiC) on morphology of low-carbon steel martensite was studied by means of electron backscatter diffraction (EBSD). The nucleation and growth of new morphology subunits such as packet, block and sub-block are observed in the area surrounding of micron-sized TiC particles. The misorientation from a fitted orientation relationship between martensite and austenite near TiC particle is larger than the average misorientation with a localized characteristic. The position of new morphology subunits has a well correspondence with the area in vicinity of TiC particle, which has large misorientation. The micron-sized TiC particle plays a role of stress concentrator in austenite during martensitic transformation which suppresses growth of one martensite variant while stimulates nucleation and growth of another one.
Authors: Fei Xiao, Kaname Yashima, Takashi Fukuda, Tomoyuki Kakeshita
Abstract: We have investigated superelastic behavior of an Fe-30.8Pd (at.%) alloy. This alloy transforms from a FCC parent phase to a FCT martensite phase at 255 K with a latent heat of 38 J/mol. When a compressive stress is applied in the [001] direction above the transformation temperature, the specimen exhibits a large elastic-like strain of more than 3% under relatively small stress of 100 MPa. The large elastic-like strain mainly comes from the elastic strain of the parent and martensite phases. The transformation strain also contributes to the strain, but it decreases linearly with increasing temperature and stress. The transformation strain || is extrapolated to be about 1.4 % under zero stress, and 0 % under 100 MPa. Probably a critical point, at which first order nature of the transformation disappears, exists for the FCC to FCT transformation in Fe-Pd alloys.
Authors: Lajos Daróczi, Tarek El Rasasi, Dezső L. Beke
Abstract: Abstract. Thermoelasic martensitic transformations are controlled by the local equilibrium of chemical and non-chemical free energy contributions (D and E being the dissipative and elastic energies, respectively). The derivatives of non-chemical free energies ( ) as a function of the transformed martensite fraction (ξ) can be expressed from the experimental data obtained from the temperature-elongation, temperature-resistance, etc hysteresis loops. This method, developed in our laboratory, was used for the investigation of non complete, partial thermoelastic transformation cycles. In the first set of experiments the subsequent cycles were started below the Mf temperature and the maximum temperature was decreased gradually from a value above Af (series U). In the second (L) set the cycles were started above the Af and the minimum temperature was gradually increased from a value below Mf. In the third (UL) set the minor loops were positioned into the centre of the two phase region (i.e. the cycling was made with an increasing T temperature interval with T0.5 and <0.5, respectively. On the other hand the d() functions show a maximum at about the central point of the sub-cycles, and deviate considerably from the d() function obtained from the full cycles. This is also reflected in the  dependence of the integral value of the dissipative energy, D(): its value for the partial loops is lower than the dissipative energy calculated from the full cycle for the same transformed fraction interval. An opposite tendency (i.e. higher values for the partial loops) was obtained for the integral value of the elastic energy, E. The relative values of the dissipated energies, D, (calculated from the areas of the minor loops and normalized to the area of the major loop) are not very sensitive to the details of the cycling process, i.e. they are very similar for all sets.
Authors: M. Carmen Gallardo, F. Javier Romero, Julia Manchado, José María Martín Olalla, Antoni Planes, Eduard Vives, Ekhard K.H. Salje, Ricardo Romero, Marcelo Stipcich
Abstract: The first-order diffusionless structural phase transition in Cu67.64Zn16.71Al15.65 is characterized by jerky propagation of phase front related to the appearance of avalanches. In this work we describe a full analysis of this avalanche behaviour using calorimetric heat-flux measurements and the results are compared with acoustic emission (AE) measurements.
Authors: Vladimir I. Nikolaev, Gennady A. Malygin, Serguey A. Pulnev, Pavel N. Yakushev, Victor M. Egorov
Abstract: Abstract. The paper is a presentation of two new phenomena which have been recently revealed and investigated by authors in well-known shape memory alloys such as Cu-Al-Ni and Ni-Fe-Ga. The first is a strong decrease of the martensitic transfornation heat evolved (absorbed) in single crystals of Cu-13.5 wt. % Al - 4.0 wt. % Ni alloy in the course of their in-situ calorimetric study under constrained shape memory deformation conditions. The second is a burst character of emerg-ing shape memory strain in the course of heating single crystals of Ni49Fe27Ga18CoSubscript text6 ferromagnetic alloy. The crystals were preliminary compressed along [110] crystallographic axis for the purpose of giving them a shape memory deformation. As a result of burst martensitic transition, the monocrystalline samples standing on a hard base and loaded additional weight of 400 g threw up this weight on 66 mm height .

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