The effect of aging temperature in the range of 300-500°C on the structure, R martensitic transformations and mechanical characteristics of nanocrystalline Ti-50.9 at % Ni alloy with a grain/subgrain structure was studied. It was found that variation in the spatial distribution of coherent Ti3Ni4 particles in the nanostructure from their location on dislocations during low-temperature aging to precipitation at dislocation boundaries under intense aging is accompanied by a change in the morphology of the R phase from a nanodomain to a self-accommodating lamellar structure. The nanodomain structure of the R phase contributes to uniform deformation of the alloy during loading/unloading and stabilization of superelasticity. When loading the alloy with a lamellar R-phase morphology, localized deformation bands are formed by the R-phase reorientation in a Luders deformation manner.

The influence of the aging temperature in the temperature range 300–500°C on the martensitic deformation response and mechanical characteristics of the Ti–50.9 at.

The features of the grain-subgrain structure of Ti49.8Ni50.2 (at. %) alloy after megaplastic deformation by multi-axial forging at 573 K and subsequent annealing were investigated by the method of backscattered electron diffraction. It is shown that the best detection of the patterns of the grain-subgrain structure of the Ti49.8Ni50.2 alloy after a given true deformation e = 9.55 and annealing at 773 K for 2 hours, it is observed in areas without martensitic relief on the surface of the samples. It was found that the clearest diffraction patterns of backscattered electrons are observed in the central part of the grains, and with distance from the center of the grain, the quality of the Kikuchi lines deteriorates. The calculation of the equivalent grain diameter showed that the average grain size is 0.203 ± 0.053 microns. The grains have mainly an ellipse shape with an axis ratio of 0.48. Elongated grains along their length have a discrete-continuous disorientation of the crystal structure, which can reach 5 degrees per 1 micrometer.

Analysis of elastic properties of Ti49Ni51 (at

X-ray diffraction studies were conducted to examine changes in the structural-phase state and dislocation density of Ti49.8Ni50.2 alloy depending on the isochronal annealing temperature after severe plastic deformation by abc pressing at 573 K. The total true strain achieved in the alloy specimens during abc pressing was e = 9.55. Isochronal annealing was carried out for 1 h at 573, 673, 773, 873 and 973 K. Analysis of all studied specimens at room temperature revealed the coexistence of R and B19′ phases, whose relative fractions varied with annealing temperature. The high-temperature B2 phase was not detected. It was found that the most rapid decrease in the dislocation density, which was measured at 393 K (in the B2 state), occurred after annealing at 673 and 773 K. Specimens annealed at 773 K had the minimum dislocation density, which is more than an order of magnitude lower than the dislocation density immediately after abc pressing. In the same temperature range, there is a significant decrease in the root-mean-square B2 lattice microdistortions <ε2>1/2 and a slight increase in the average size of coherently diffracting domains (crystallities). After abc pressing and isochronal annealing, the main contribution to the intrinsic X-ray line broadening is made by B2 lattice microdistortions, while the contribution from crystallite size is insignificant. The obtained results show that intense recrystallization in Ti49.8Ni50.2 alloy after abc pressing at 573 K begins at T ≥ 773 K.

The development of inelastic and plastic strains is studied for Ti49.3Ni50.7 (at.

The development of inelastic and plastic strains is studied for Ti49.3Ni50.7 (at.%) alloy samples with the structure of high-temperature B2 phase in the state as received from the manufacturer under torsion. It has been established that when the strain of the samples, specified by torsion, is equal to 10.6%, the value of the accumulated plastic strain is 0.35%. Therefore, the actual yield stress of the Ti49.3Ni50.7 (at.%) alloy samples is localized at the end of the pseudo-yield plateau on the stress-strain dependence rather than at the end of the strain hardening stage, as previously thought. The results presented in the work should be taken into account in the practical use of the alloy with this composition as products for technical and medical purposes that experience tensile, bending, and torsional deformations.

Effects of the size, morphology, and spatial distribution of coherent Ti3Ni4 particles in a nanocrystalline Ti– 50.9 at.

X-ray diffraction studies were conducted to examine changes in the structural-phase state and dislocation density of Ti498Ni50.2 alloy depending on the isochronous annealing temperature after severe plastic deformation by abc pressing at 573 K. The total true strain achieved in the alloy samples during abc pressing was e = 9.55. Isochronous annealing was carried out for 1 hour at 573, 673, 773, 873 and 973 K. Room-temperature analysis of all studied samples revealed the coexistence of R and B19' phases, whose relative fractions varied with annealing temperature. The high-temperature B2 phase was not detected. It was found that the most rapid decrease in the dislocation density, which was measured at 393 K (in the B2 state), occurs after annealing the samples at 673 and 773 K. After annealing at 773 K, the dislocation density reaches a minimum, and its value decreases by more than an order of magnitude compared to the value immediately after abc pressing. In the same temperature range there is a significant decrease in the root-mean-square B2 lattice microdistortions (e2)1/2 and a slight increase in the average size of coherent scattering regions. After abc pressing and after isochronous annealing, the main contribution to the physical peak broadening is made by the B2 lattice microdistortions, while the contribution from coherent scattering regions is insignificant. The obtained results show that intense recrystallization in Ti49 8Ni50.2 alloy after abc pressing at 573 K begins at T > 773 K.

The paper reports on a nanoindentation study of the hardness H and Young’s modulus E in the B2 phase of quasi-binary TiNi-TiFe single crystals and Ti49Ni51 single and polycrystals with and with no thermoelastic martensite transformations. The study shows that the elastic properties of the alloy single crystals depend on the concentration of Fe atoms and decrease gradually with a decrease in the Fe content and with a gradual decrease in the B2-phase stability to martensite transformations. In Ti50Ni50–xFex, the dependence of the hardness H on the Fe content reveals a peak at equal Fe and Ni concentrations (25.0 at

In this paper, to analyze the elastic properties of Ti49Ni51 (at. %) and TiNi – TiFe crystals with and without martensitic transformations Every’s and Blackman’s diagrams are used as two ways to characterize the elastic properties of cubic materials. Paired correlations between the parameters (s2, s3), (s3, s1) и (F44, F12) are calculated. The evolution of the Cauchy pressure pC value depending on the content of iron atoms in the crystal lattice of alloys is considered. It is established that, regardless of the composition of the alloys, the Cauchy pressure is greater than zero and decreases almost monotonically from 100.5 to 35.0 GPa with an increase in the content of Fe atoms in the B2 crystal lattice of the TiNi – TiFe phase and an increase in its stability with respect to martensitic transformations (up to complete stabilization). This evolution of pC corresponds to the data according to which a significant component of the bonding forces in TiNi is a metallic bond, and with an increase in the concentration of Fe atoms in alloys instead of Ni atoms and approaching the composition of TiFe, the proportion of the covalent component of the bonding forces increases.

The regularities and features of the evolution of the grain–subgrain structure, phase composition and mechanical properties in Ti49.8Ni50.2 (at.%), depending on the temperature of isochronous annealings at 573–973 K are herein studied. The state of the Ti49.8Ni50.2 (at.%) alloy samples after abc pressing at T = 573 K with the given true strain e = 9.55 was taken as the initial state. It is shown that the grain–subgrain structure of the samples after annealing for 1 h in the temperature range of 573–673 K changes slightly. In samples annealed at 673 K, regions with the microband structure similar to the microstructure of a fast-frozen turbulent liquid flow were found. It has been established that during annealing at 773 K the beginning of an active recrystallization process is realized; the size of grains does not exceed the submicrocrystalline scale (~200 nm). At 873 K, the recrystallization process occurs in the entire volume of the samples; the grains with an average size of 2 ± 0.5 µm are almost equiaxed. The microstructure of the samples after annealing at 973 K (with average grain sizes of 5 ± 0.5 µm) is qualitatively similar to the microstructure of the samples after annealing at 873 K. It was found that the phase composition of the samples as a result of isochronous annealing at 573–973 K changes from R and B19’ immediately after abc pressing to a three-phase state: B2, R and B19’ phases. It is shown that the highest values of yield stress σy, ultimate tensile strength σUTS (1043 MPa and 1232 MPa, correspondingly) and low ductility (the deformation to fracture εf = 48%) are observed in the initial samples. Increasing the temperature of post-deformation annealing and, correspondingly, the development of recrystallization, led to a decrease in σy, σUTS and an increase in εf to the values of these characteristics in the coarse-grained samples (σy = 400 MPa, σUTS = 920 MPa and εf = 90%).

This paper presents the results of a transmission electron microscope study of the influence of the size, morphology, and spatial distribution of coherent Ti3Ni4 particles on the nature of the R transformation; the morphology of the R phase; and the deformation response depending on the aging temperature in nanocrystalline Ti–50.9 at.% Ni alloy with a grain–subgrain structure. It has been established that with an increase in the aging temperature, the size and spatial distribution of Ti3Ni4 particles change from being located on dislocations at an aging temperature of 300 °C to precipitation at sub-boundaries at an aging temperature of 400 °C, 450 °C. Correspondingly, the morphology of the R phase changes from nanodomain-like to a lamellar self-accommodation structure. Studies have shown that the morphology of the R phase, in turn, affects the deformation response of the material. In the case of lamellar self-accommodation morphology, localized R transformation develops in a Lüders-like manner.

The experimental results regarding the effect of warm (573 K) abc pressing with an increase in the specified true strain, e, up to 9.55, on the microstructure and crystal structure defects (dislocations, vacancies) of the Ti49.8Ni50.2 (at %) alloy are presented. It is shown that all samples (regardless of e) have a two-level microstructure. The grains–subgrains of the submicrocrystalline scale level are in the volumes of large grains. The average sizes of both large grains and subgrain grains decrease with increasing e to 9.55 (from 27 to 12 µm and from 0.36 to 0.13 µm, respectively). All samples had a two-phase state (rhombohedral R and monoclinic B19′ martensitic phases) at 295 K. The full-profile analysis of X-ray reflections of the B2 phase obtained at 393 K shows that the dislocation density increases from 1014 m−2 to 1015 m−2 after pressing with e = 1.84 and reaches 2·1015 m−2 when e increases to 9.55. It has been established by positron annihilation lifetime spectroscopy that dislocations are the main type of defects in initial samples and the only type of defects in samples after abc pressing. The lifetime of positrons trapped by dislocations is 166 ps, and the intensity of this component increases from 83% in the initial samples to 99.4% after pressing with e = 9.55. The initial samples contain a component with a positron lifetime of 192 ps (intensity 16.4%), which corresponds to the presence of monovacancies in the nickel sublattice of the B2 phase (concentration ≈10−5). This component is absent in the positron lifetime spectra in the samples after pressing. The results of the analysis of the Doppler broadening spectroscopy correlate with the data obtained by the positron annihilation lifetime spectroscopy.

Specific features of the spatial distribution of Ti 3 Ni 4 particles in the inhomogeneous grain/subgrain structure of the nanocrystalline Ti − 50.9 at.% Ni alloy are identified depending on the aging temperature. It is found out that the presence of an ensemble of internal interfaces of various types in the nanostructure promotes a heterogeneous distribution of Ti 3 Ni 4 nanoparticles in the volume of the B2 matrix, which is associated with the precipitation of particles in the region of low-angle subgrain boundaries and the suppression of the decomposition of a solid solution in nanograins with high-angle boundaries. The relationship between the evolution of the system of Ti 3 Ni 4 precipitates during heat treatment and the staging of martensitic transformations in the nanocrystalline TiNi alloy with an inhomogeneous grain/subgrain structure is investigated. It is shown that the difference in the structural-phase states of the substructure and the nanograins is the main reason for the anomalous effect of the R-phase transformation in the sequence of multistage martensitic transformations B2 ↔ R ↔ B19 '.

We develop a Floquet protocol for long-range entanglement generation in the one-dimensional quantum Potts model, which generalizes the transverse-filed Ising model by allowing each spin to have $n>2$ states. We focus on the case of $n=3$, so that the model describes a chain of qutrits. The suggested protocol creates qutrit Bell-like pairs with non-local long-range entanglement that spans over the entire chain. We then conjecture that the proposed Floquet protocol is integrable and explicitly construct a few first non-trivial conserved quantities that commute with the stroboscopic evolution operator. Our analysis of the Floquet integrability relies on the deep connection between the quantum Potts model and a much broader class of models described by the Temperley-Lieb algebra. We work at the purely algebraic level and our results on Floquet integrability are valid for any representation of the Temperley-Lieb algebra. We expect that our findings can be probed with present experimental facilities using Rydberg programmable quantum simulators and can find various applications in quantum technologies.

The mechanical properties of Ti49.8Ni50.2 (at %) alloy under tension at room temperature are studied in dependence on the true strain (e = 1.84–9.55) specified during isothermal multi-axial forging (abc-pressing). It was found that the stress at the beginning of the pseudoyield plateau does not depend on the value of the true abc-strain. It was found that after abs-pressing, already at a true strain e = 1.84, the yield stress σy was 900 ± 25 MPa, which is more than twice as high as compared to σy in the initial state of the specimens. With a further increase in the abc-strain, the yield stress continues to increase slightly and reaches 1000 ± 25 MPa at e = 9.55. In this case, the ultimate tensile strength of the samples increases by about 15%. The strain-hardening coefficient ϴ = dσ/dε at the III (linear) stage of the σ(ε) curve has a similar dependence on e. It is shown that after abc-pressing with e from 1.84 to 9.55, the yield stress and ultimate tensile increase linearly with increasing d−1/2 in accordance with the Hall–Petch relation, where d is the average grain–subgrain size.

The influence of the abc pressing temperature on the mechanical properties of the Ti49.8Ni50.2 alloy has been studied. It is shown that the decrease in the abc pressing temperature from 723 to 573 K did not lead to a significant decrease in the average size of the grain-subgrain structure. However, it caused a slight increase in the strength characteristics of the alloy while maintaining quite high ductility. Possible factors determining the lower efficiency of abc pressing in terms of its effect on mechanical characteristics compared to other SPD methods at comparable values of true strain e are discussed.

A review of the published data and methods for calculating the Poisson ratio of the TiNi intermetallic compound in the poly- and single-crystal state is performed. The results of our own research are also presented. Significant variability of the presented data is noted, which is due to differences in the thermomechanical processing of the alloys and the measurement and calculation methods used. By averaging the matrices of elastic constants and compliance coefficients using the Voigt, Reuss, and Hill approximations, we obtained the values of the parameters of the effective elastic properties of TiNi polycrystals and calculated the Poisson ratio. Using analytical expressions to calculate the values of the extreme values, the extrema of the Poisson ratio of cubic TiNi crystals are determined for standard orientations. On the basis of a number of data, TiNi crystals are auxetics (materials having negative Poisson ratio values); on the basis of other data, they are not. We found that TiNi crystals belong to the so-called partial auxetics; in this case, the signs of the inequalities (s12 < 0, s = s11 + s12 – s44/2 > 0 or s12 > 0, s = s11 + s12 – s44/2 < 0) are opposite. The values of the Poisson ratio TiNi averaged over the transverse directions of deformation are analyzed. Isosurfaces of the Poisson ratio and their sections are presented using the ELATE computer graphics package and the M-ATHCAD computer algebra program. Aspects of TiNi elastic anisotropy, its parameters, and their relationship to martensitic transformations in TiNi and alloys based on it are discussed.