E. S. Belosludtseva

High-temperature shape memory effect and the B2-L10 thermoelastic martensitic transformation in Ni-Mn intermetallics

The properties and structure of the martensitic phase of alloys with a near-stoichiometric equiatomic Ni50Mn50 composition, as well as martensitic transformations in them, are investigated in a wide temperature range by measuring the resistivity and thermal expansion coefficient and applying transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. It is found that Ni50Mn50 and Ni49Mn51 alloys experience the B2 → L10 highly reversible thermoelastic martensitic transformation and its related high-temperature deformation of the transformation and shape memory effect. Critical temperatures, volume (ΔV/V = ∓1.7%) and linear size effects attributed to the direct and reverse martensitic transformations, and the high-temperature dependences of the martensitic and austenite lattice parameters are determined. It is found that the morphology of tetragonal L10 martensitic represents a hierarchy of thin coherent sheets of submicrocrystallites and nanocrystallites with plane near-{111}L10 habit boundaries, the crystallites being pairwise twinned according to the {111}〈11

Magnetic and structural phase transitions and the tetragonality of thermoelastic martensite in quasi-binary Heusler alloys Ni2 + xMn1 − xGa

\bar 2

Fine structure and mechanical properties of the shape-memory Ni 50 Ti 32 Hf 18 alloy rapidly quenched by spinning

〉L10 ∥ {011}〈-1

Crystallographic features of the structure of a martensite packet of the NiMn intermetallic compound

\bar 1

Peculiarities of the phase composition and structure of the high-entropy FeWMoCrVSiMnC multicomponent steel

〉B2 twinning shear scheme.

Magnetically controlled thermoelastic martensite transformations and properties of a fine-grained Ni54Mn21Ga25 alloy

This paper reports on the results of investigations into the structure of martensite and the electronic and magnetic properties of Ni2 + xMn1 − xGa alloys in the concentration range 0.12 ≤ x ≤ 0.39. The concentration dependences of the critical temperatures and the anomalous behavior of the degree of tetragonal distortion of the martensite have been discussed, as well as the changes in the parameters characterizing the electronic and magnetic subsystems in the thermoelastic martensitic transition L21 ↔ M, which occurs in atomically ordered L21-type alloys upon doping in the range 0.12 ≤ x ≤ 0.39 at different temperatures. The temperature and concentration dependences of the magnetic properties have been determined for the state of the single-phase L21 austenite (at T > TC and Af) and martensite (at T < TC and Mf), which undergoes the transition from a modulated 10M- or 14M-type structure to a nonmodulated (NM) tetragonal structure.

Thermoelastic martensitic transformations in ternary Ni50Mn50–zGaz alloys

We have reported the results of investigations of the structure and chemical and phase compositions of the amorphous Ni50Ti32Hf18 alloy prepared by rapid quenching from melt by spinning and subjected to heat treatments. The specific features of the fine polycrystalline alloy structure formation depending on the heat-treatment mode have been studied by transmission and scanning electron microscopy, chemical microanalysis, electron diffraction, and X-ray diffraction analysis. According to the data on the temperature behavior of electrical resistivity, critical temperatures of devitrification and subsequent thermoelastic martensitic transformation B2 → B19′ have been determined. The mechanical properties in different heat-treatment modes have been investigated.

Effect of titanium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni—Mn—Ti alloys

Optical microscopy, scanning electron microscopy, and X-ray diffraction are used to show that a pseudosingle crystal forms upon cooling of an alloy Ni49Mn51 single crystal below the temperature of the β→θ (bcc → fct) transformation. At room temperature, this pseudosingle crystal has the structure of tetragonal L10 martensite with parameters a = 0.3732 nm and c = 0.3537 nm and a tetragonality c/a = 0.94775. The temperatures of the forward and reverse B2 → L10 transformations are determined. The crystallographic features of martensite packet formation are analyzed. As shown by EBSD, neighboring martensite packets always have three kinds of tetragonal martensite plates, which are in a twin position and have different tetragonality axis directions. Repeated heating and quenching of the pseudosingle crystal result in recrystallization with the formation of coarse grains. The packet structure of the tetragonal martensite is retained in this case, and the sizes of the packets formed within a grain decrease by a factor of 2–3 as compared to the initial pseudosingle crystal.

Features of Martensitic Transformation and Fine Structure of Intermetallic Compound Ni 50 Mn 50

We report on the results of analysis of the phase composition, structure, and hardness of high-entropy FeWMoCrVSiMnC multicomponent steel subjected to synthesis and subsequent thermal treatment. Analysis is carried out using the methods of analytic transmission and scanning structural and orientational electron microscopy, optical metallography, X-ray energy-dispersive spectroscopy, X-ray phase and structural analyses, and Rockwell measurements of hardness. It is found that steel has a high hardness (62 HRC) and is in ultra-fine-disperse composite martensite-multicarbide state. All carbides are distributed uniformly over the steel volume and have nano- and submicrometer scales depending on the carbide type.

Thermoelastic Martensitic Transitions and Shape Memory Effects: Classification, Crystal and Structural Mechanisms of Transformations, Properties, Production and Application of Promising Alloys

Comparative studies of physical characteristics (the electrical resistivity, the magnetic susceptibility, the magnetization, the bending deformation, and the degree of shape recovery during subsequent heating) of the Ni54Mn21Ga25 ferromagnetic alloy as-cast and rapidly quenched from melt have been performed in the temperature range 2–400 K. The results are compared to the results of studying the structural–phase transformations by transmission and scanning electron microscopy and X-ray diffraction. It is found that the rapid quenching influences the microstructure, the magnetic state, the critical temperatures, and the specific features of thermoelastic martensite transformations in the alloy. It is found that the resource of the alloy plasticity and thermomechanical bending cyclic stability demonstrates a record-breaking increase in the intercritical temperature range and during subsequent heating.