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Nowadays, all thermo-mechanical effects, associated with the martensitic structural phase transitions, are still in the focus of scientists and engineers, especially once these phenomena are taking place at elevated temperatures. The list of the materials, undergoing high-temperature martensitic transformation, is constantly widening. Still, industrial application of these materials, called hightemperature shape memory alloys, is far enough due to the lack of understanding of the peculiarities of the high-temperature martensitic transformation and shape memory effect. The present work attempts to show how the development of the proper directions for high-temperature shape memory alloys' improvement might lead to the creation of essentially new functional materials.Keywords Martensitic phase transformation Á Crystal and electronic structure Á Shape memory behaviour Á High temperature shape memory alloys Á High entropy alloys

Abstract. It was shown very recently that despite high thermal stability some high entropy alloys, namely, intermetallic compounds of TiZrHfCoNiCu family, undergo martensitic transformation and exhibit shape memory effect [1]. It was also found that X-ray diffraction patterns taken from those compounds resemble qualitatively ones of B2 ordering type for austenitic state and B19` -for martensite. It is going to be shown [2] that the ordered structure of austenite phase is not B2 but is a result of group-subgroup transition down to triclinic P1 space group. Present paper reports onto the results of electron structure modelling combined with crystal structure analysis with the help of experimental data Rietveld refinement performed for TiZrHfCoNiCu intermetallics. Crystal structures of austenite and martensite phases for these high entropy intermetallics will be discussed.

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The present study is dedicated to the microstructure characterization of the as-cast high entropy intermetallics that undergo a martensitic transformation, which is associated with the shape memory effect. It is shown that the TiZrHfCoNiCu system exhibits strong dendritic liquation, which leads to the formation of martensite crystals inside the dendrites. In contrast, in the CoNiCuAlGaIn system the dendritic liquation allows the martensite crystals to form only in interdendritic regions. This phenomenon together with the peculiarities of chemical inhomogeneities formed upon crystallization of this novel multicomponent shape memory alloys systems will be analyzed and discussed.

Phase equilibria in the Ni-Zr system were experimentally reinvestigated by means of differential thermal, electron microprobe, X-Ray diffraction and metallographic analyses of the alloys, which were prepared by arc melting and then annealed at 900°C during 2 weeks. The temperatures of equilibria reactions in Ni-Zr systems were specified and phase diagram Ni-Zr was reconstructed.

The crystal structure changes in Ni 3 Ta were experimentally investigated by X-ray powder diffraction of alloys prepared by arc melting, ground and annealed in the temperature range 673-1173 K for 1 day. It was found that an increase of the annealing temperatures leads to a change of the product of the transformation of the high-temperature tetragonal phase from monoclinic to orthorhombic. The changes are promoted by recovery and recrystallization processes. Some oxidation at the higher annealing temperatures led to the reappearance of the phase with monoclinic structure.