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15 pages, 3143 KiB

Open AccessArticle

Crystal Structure Defects in Titanium Nickelide after Abc Pressing at Lowered Temperature

by Aleksandr Lotkov, Victor Grishkov, Roman Laptev, Yuri Mironov, Dorzhima Zhapova, Natalia Girsova, Angelina Gusarenko, Elena Barmina and Olga Kashina

Materials 2022, 15(12), 4298; https://doi.org/10.3390/ma15124298 - 17 Jun 2022

Cited by 5 | Viewed by 1958

Abstract

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 Ti_49.8Ni_50.2 (at %) alloy [...] Read more.

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 Ti_49.8Ni_50.2 (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. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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16 pages, 12221 KiB

Open AccessArticle

Mechanical Behavior and Structural Characterization of a Cu-Al-Ni-Based Shape-Memory Alloy Subjected to Isothermal Uniaxial Megaplastic Compression

by Vladimir Pushin, Nataliya Kuranova, Alexey E. Svirid and Yurii Ustyugov

Materials 2022, 15(10), 3713; https://doi.org/10.3390/ma15103713 - 22 May 2022

Cited by 5 | Viewed by 2263

Abstract

For the first time, uniaxial megaplastic compression was successfully applied to a polycrystalline shape-memory Cu-Al-Ni-based alloy. The samples before and after uniaxial megaplastic compression were examined by methods of X-ray diffraction, optical, electron transmission, and scanning microscopy. The temperature dependences of electrical resistance [...] Read more.

For the first time, uniaxial megaplastic compression was successfully applied to a polycrystalline shape-memory Cu-Al-Ni-based alloy. The samples before and after uniaxial megaplastic compression were examined by methods of X-ray diffraction, optical, electron transmission, and scanning microscopy. The temperature dependences of electrical resistance and the mechanical properties of the alloys under uniaxial tension were also measured. The mechanical behavior under uniaxial megaplastic compression in isothermal conditions in the range of 300–1073 K was studied using the Instron 8862 electric testing machine. The microstructure, phase composition, and martensitic transformations in the eutectoid alloy (Cu-14wt.%Al–4 wt.%Ni) were studied. The radical refinement of the grain structure of the initial hardened D0₃ austenite was found under controlled isothermal compression, due to dynamic recrystallization in the temperature range 673–1073 K and velocities of 0.5–5 mm/min. Compression at 873–1073 K was accompanied by simultaneous partial pro-eutectoid decomposition with the precipitation of the γ₂ phase. Compression at temperatures of 673 and 773 K—that is, below the eutectoid decomposition temperature (840 K)—was accompanied by the precipitation of disperse γ₂ and α phases, and ultradisperse B2’ particles. Cooling of the deformed alloy to room temperature after performing each regime of compression led to thermoelastic martensitic transformation, together with the precipitation of the β′ and γ′ phases. The formation of a fine-grained structure produced an unusual combination of strength and plasticity of the initially brittle alloy both under controlled uniaxial compression, and during subsequent tensile tests at room temperature. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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12 pages, 7670 KiB

Open AccessArticle

New Metastable Baro- and Deformation-Induced Phases in Ferromagnetic Shape Memory Ni₂MnGa-Based Alloys

by Vladimir Pushin, Alexander Korolyov, Nataliya Kuranova, Elena Marchenkova and Yurii Ustyugov

Materials 2022, 15(6), 2277; https://doi.org/10.3390/ma15062277 - 19 Mar 2022

Cited by 6 | Viewed by 2010

Abstract

Structural and phase transformations in the microstructure and new metastable baro- and deformation-induced phases of the Ni₅₀Mn_28.5Ga_21.5 alloy, typical of the unique class of ferromagnetic shape memory Heusler alloys, have been systematically studied for the first time. Phase [...] Read more.

Structural and phase transformations in the microstructure and new metastable baro- and deformation-induced phases of the Ni₅₀Mn_28.5Ga_21.5 alloy, typical of the unique class of ferromagnetic shape memory Heusler alloys, have been systematically studied for the first time. Phase X-ray diffraction analysis, transmission and scanning electron microscopy, and temperature measurements of electrical resistivity and magnetic characteristics in strong magnetic fields were used. It was found that in the course of increasing the pressure from 3 to 12 GPa, the metastable long-period structure of martensite modulated according to the 10M-type experienced transformation into a final non-modulated 2M structure. It is proved that severe shear deformation by high pressure torsion (HPT) entails grainsize refinement to a nanocrystalline and partially amorphized state in the polycrystalline structure of the martensitic alloy. In this case, an HPT shear of five revolutions under pressure of 3 GPa provided total atomic disordering and a stepwise structural-phase transformation (SPT) according to the scheme 10M → 2M → B2 + A2, whereas under pressure of 5 GPa the SPT took place according to the scheme 10M → 2M → B2 → A1. It is shown that low-temperature annealing at a temperature of 573 K caused the amorphous phase to undergo devitrification, and annealing at 623–773 K entailed recrystallization with the restoration of the L2₁ superstructure in the final ultrafine-grained state. The size effect of suppression of the martensitic transformation in an austenitic alloy with a critical grain size of less than 100 nm at cooling to 120 K was determined. It was established that after annealing at 773 K, a narrow-hysteresis thermoelastic martensitic transformation was restored in a plastic ultrafine-grained alloy with the formation of 10M and 14M martensite at temperatures close to those characteristic of the cast prototype of the alloy. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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11 pages, 3298 KiB

Open AccessArticle

Structure and Phase State of Ti_49.4Ni_50.6 (at%) Hydrogenated in Normal Saline

by Victor Grishkov, Aleksandr Lotkov, Dorzhima Zhapova, Yuri Mironov, Victor Timkin, Elena Barmina and Olga Kashina

Materials 2021, 14(22), 7046; https://doi.org/10.3390/ma14227046 - 20 Nov 2021

Cited by 5 | Viewed by 1390

Abstract

The paper analyzes the surface structure and phase state of Ti_49.4Ni_50.6 (at%) hydrogenated at 295 K in normal saline (0.9% NaCl aqueous solution with pH = 5.7) at 20 A/m² for 0.5–6 h. The analysis shows that the average [...] Read more.

The paper analyzes the surface structure and phase state of Ti_49.4Ni_50.6 (at%) hydrogenated at 295 K in normal saline (0.9% NaCl aqueous solution with pH = 5.7) at 20 A/m² for 0.5–6 h. The analysis shows that the average hydrogen concentration in the alloy increases with the hydrogenation time t_H as follows: slowly to 50 ppm at t_H = 0.5–1.5 h, steeply to 150 ppm at t_H = 1.2–2 h, and linearly to 300 ppm at t_H = 2–6 h. According to Bragg–Brentano X-ray diffraction data (θ–2 θ, 2 θ ≤ 50°, CoKα radiation), the alloy in its scanned surface layer of thickness ~5.6 µm reveals a TiNiH_x phase with x = 0.64 and x = 0.54 after hydrogenation for 4 and 6 h, respectively. The structure of this phase is identifiable as an orthorhombic hydride similar to β₁–TiFeH_0.94 (space group Pmcm), rather than as a tetragonal TiNiH_x hydride with x = 0.30–1.0 (space group I4/mmm). Time curves are presented to trace the lattice parameters and volume change during the formation of such an orthorhombic phase from the initial cubic B2 phase in Ti_49.4Ni_50.6 (at%). Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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13 pages, 3829 KiB

Open AccessArticle

Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy

by Francesca Villa, Adelaide Nespoli, Francesca Passaretti and Elena Villa

Materials 2021, 14(14), 3770; https://doi.org/10.3390/ma14143770 - 6 Jul 2021

Cited by 5 | Viewed by 2478

Abstract

Among NiTi-based alloys, one of the most promising and exploited alloys is NiTiCu, since the addition of Cu in substitution of Ni in the binary equiatomic NiTi has a significant influence on the martensitic transformation and the thermomechanical properties of the system. A [...] Read more.

Among NiTi-based alloys, one of the most promising and exploited alloys is NiTiCu, since the addition of Cu in substitution of Ni in the binary equiatomic NiTi has a significant influence on the martensitic transformation and the thermomechanical properties of the system. A high content of Cu improves the damping properties at the expense of phase homogeneity and workability. The present study focuses on an alloy with a high copper content, i.e., 20 at.%. For this specific composition, the correlation between the thermal treatments, microstructure, formation of secondary phases, and damping properties are investigated by several analyses. The microscopic observation, together with the compositional analysis, allowed the determination of four different phases in the alloy. Both the calorimetry and dynamic thermo mechanical measurements, which confirmed the high damping ability of the alloy, provided a characterization of the martensitic transition. Finally, the electron backscatter diffraction (EBSD) analysis detected the different crystallographic structures (i.e., cubic austenite, orthorhombic martensite, and cubic (face-centered) NiTi₂) and their orientation in the different phases. Therefore, the present work aims to improve the knowledge of the role of secondary phases in the optimization of the NiTiCu20 alloy as a valuable alternative to typical alloys used for damping purposes. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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12 pages, 6609 KiB

Open AccessArticle

Microstructure Formation in Cast TiZrHfCoNiCu and CoNiCuAlGaIn High Entropy Shape Memory Alloys: A Comparison

by Tetiana A. Kosorukova, Gregory Gerstein, Valerii V. Odnosum, Yuri N. Koval, Hans Jürgen Maier and Georgiy S. Firstov

Materials 2019, 12(24), 4227; https://doi.org/10.3390/ma12244227 - 16 Dec 2019

Cited by 14 | Viewed by 3990

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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12 pages, 2400 KiB

Open AccessArticle

The Effect of Hydrogen on Martensite Transformations and the State of Hydrogen Atoms in Binary TiNi-Based Alloy with Different Grain Sizes

by Anatoly Baturin, Aleksandr Lotkov, Victor Grishkov, Ivan Rodionov, Yerzhan Kabdylkakov and Victor Kudiiarov

Materials 2019, 12(23), 3956; https://doi.org/10.3390/ma12233956 - 28 Nov 2019

Cited by 9 | Viewed by 2580

Abstract

The analysis presented here shows that in B2-phase of Ti_49.1Ni_50.9 (at%) alloy, hydrogenation with further aging at room temperature decreases the temperatures of martensite transformations and then causes their suppression, due to hydrogen diffusion from the surface layer of specimens [...] Read more.

The analysis presented here shows that in B2-phase of Ti_49.1Ni_50.9 (at%) alloy, hydrogenation with further aging at room temperature decreases the temperatures of martensite transformations and then causes their suppression, due to hydrogen diffusion from the surface layer of specimens deep into its bulk. When hydrogen is charged, it first suppresses the transformations B2↔B19′ and R↔B19′ in the surface layer, and when its distribution over the volume becomes uniform, such transformations are suppressed throughout the material. The kinetics of hydrogen redistribution is determined by the hydrogen diffusion coefficient D_H, which depends on the grain size. In nanocrystalline Ti_49.1Ni_50.9 (at%) specimens, D_H is three times greater than its value in coarse-grained ones, which is likely due to the larger free volume and larger contribution of hydrogen diffusion along grain boundaries in the nanocrystalline material. According to thermal desorption spectroscopy, two states of hydrogen atoms with low and high activation energies of desorption exist in freshly hydrogenated Ti_49.1Ni_50.9 (at%) alloy irrespective of the grain size. On aging at room temperature, the low-energy states disappear entirely. Estimates by the Kissinger method are presented for the binding energy of hydrogen in the two states, and the nature of these states in binary hydrogenated TiNi-based alloys is discussed. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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18 pages, 3410 KiB

Open AccessArticle

Hybrid Shape Memory Alloy-Based Nanomechanical Resonators for Ultrathin Film Elastic Properties Determination and Heavy Mass Spectrometry

by Ivo Stachiv and Lifeng Gan

Materials 2019, 12(21), 3593; https://doi.org/10.3390/ma12213593 - 31 Oct 2019

Cited by 10 | Viewed by 2684

Abstract

Micro-/nanomechanical resonators are often used in material science to measure the elastic properties of ultrathin films or mass spectrometry to estimate the mass of various chemical and biological molecules. Measurements with these sensors utilize changes in the resonant frequency of the resonator exposed [...] Read more.

Micro-/nanomechanical resonators are often used in material science to measure the elastic properties of ultrathin films or mass spectrometry to estimate the mass of various chemical and biological molecules. Measurements with these sensors utilize changes in the resonant frequency of the resonator exposed to an investigated quantity. Their sensitivities are, therefore, determined by the resonant frequency. The higher resonant frequency and, correspondingly, higher quality factor (Q-factor) yield higher sensitivity. In solution, the resonant frequency (Q-factor) decreases causing a significant lowering of the achievable sensitivity. Hence, the nanomechanical resonator-based sensors mainly operate in a vacuum. Identification by nanomechanical resonator also requires an additional reference measurement on the identical unloaded resonator making experiments, due to limiting achievable accuracies in current nanofabrication processes, yet challenging. In addition, the mass spectrometry by nanomechanical resonator can be routinely performed for light analytes (i.e., analyte is modelled as a point particle). For heavy analytes such as bacteria clumps neglecting their stiffness result in a significant underestimation of determined mass values. In this work, we demonstrate the extraordinary capability of hybrid shape memory alloy (SMA)-based nanomechanical resonators to i) notably tune the resonant frequencies and improve Q-factor of the resonator immersed in fluid, ii) determine the Young’s (shear) modulus of prepared ultrathin film only from frequency response of the resonator with sputtered film, and iii) perform heavy analyte mass spectrometry by monitoring shift in frequency of just a single vibrational mode. The procedures required to estimate the Young’s (shear) modulus of ultrathin film and the heavy analyte mass from observed changes in the resonant frequency caused by a phase transformation in SMA are developed and, afterward, validated using numerical simulations. The present results demonstrate the outstanding potential and capability of high frequency operating hybrid SMA-based nanomechanical resonators in sensing applications that can be rarely achieved by current nanomechanical resonator-based sensors. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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14 pages, 7294 KiB

Open AccessArticle

Yield Stress and Reversible Strain in Titanium Nickelide Alloys after Warm Abc Pressing

by Aleksander Lotkov, Victor Grishkov, Anatoly Baturin, Victor Timkin and Dorzhima Zhapova

Materials 2019, 12(19), 3258; https://doi.org/10.3390/ma12193258 - 6 Oct 2019

Cited by 2 | Viewed by 2663

Abstract

The results of the position analysis of the yield stress τ_0.3 on the "stress–strain" (τ–γ) dependences, received at the torsion of specimens of Ti_49.8Ni_50.2 (at%) alloy are presented. The critical stress τ_0.3 (IV), corresponding to the end of [...] Read more.

The results of the position analysis of the yield stress τ_0.3 on the "stress–strain" (τ–γ) dependences, received at the torsion of specimens of Ti_49.8Ni_50.2 (at%) alloy are presented. The critical stress τ_0.3 (IV), corresponding to the end of linear stage III and the beginning of the intensive development of plastic strain at stage IV, preceding the fracture of the specimens, were obtained as well. The structure of the specimens was transformed from coarse-grained to microcrystalline as a result of warm (723 K) abc pressing with a true deformation e of 8.4. The regularities of the development of reversible inelastic strain (superelasticity, SE, and shape memory effect, SME) and plastic strain γ_pl after isothermal (295 K) loading of specimens up to τ ≤ τ_0.3(IV), unloading, and their subsequent heating up to 500 K are studied. From the joint analysis of the “τ–γ” dependences obtained at 295 K and "plastic strain–total strain" dependences the yield stress τ_0.3 corresponding to the development of 0.3% of the plastic strain under loading of the specimens was determined. Critical stress τ_0.3(IV) was determined as equal to the stress corresponding to a deviation of 0.3% from the linear “τ–γ”dependence at stage III. It is shown that the yield stress τ_0.3 for all specimens is localized at the beginning of stage III for all specimens. The ratio τ_0.3(IV)/τ_0.3 is from 2.3 to 3.8. The accumulation of plastic strain at stage III (after loading with τ from τ_0.3 to τ_0.3(IV)) is from 2.4% to 4.7% (depending on the true deformation of the specimens during warm abc pressing). Thus, stage III is the stage of deformation hardening of specimens under torsion. On the basis of the results of this and previous works it is shown that, in alloys with thermoelastic martensitic transformations and with thermomechanical memory, the ratio τ_0.3(IV)/τ_0.3 can vary in a wide range: in reinforced specimens τ_0.3 can be close to τ_0.3(IV), and in more ductile specimens τ_0.3 can be significantly less than τ_0.3(IV). However, in order to correctly determine the yield stress of τ_0.3 and the corresponding strain γ_t(0.3), it is necessary to carry out a joint analysis of “τ–γ” and "plastic strain–total strain" dependencies. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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9 pages, 2668 KiB

Open AccessArticle

Crystallization Features of Amorphous Rapidly Quenched High Cu Content TiNiCu Alloys upon Severe Plastic Deformation

by Alexander Glezer, Nikolay Sitnikov, Roman Sundeev, Alexander Shelyakov and Irina Khabibullina

Materials 2019, 12(17), 2670; https://doi.org/10.3390/ma12172670 - 22 Aug 2019

Cited by 4 | Viewed by 3522

Abstract

In recent years, the methods of severe plastic deformation and rapid melt quenching have proven to be an effective tool for the formation of the unique properties of materials. The effect of high-pressure torsion (HPT) on the structure of the amorphous alloys of [...] Read more.

In recent years, the methods of severe plastic deformation and rapid melt quenching have proven to be an effective tool for the formation of the unique properties of materials. The effect of high-pressure torsion (HPT) on the structure of the amorphous alloys of the quasi-binary TiNi–TiCu system with a copper content of more than 30 at.% produced by melt spinning technique has been analyzed using the methods of scanning electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry (DSC). The structure examinations have shown that the HPT of the alloys with a Cu content ranging from 30 to 40 at.% leads to nanocrystallization from the amorphous state. An increase in the degree of deformation leads to a substantial change in the character of the crystallization reflected by the DSC curves of the alloys under study. The alloys containing less than 34 at.% Cu exhibit crystallization peak splitting, whereas the alloys containing more than 34 at.% Cu exhibit a third peak at lower temperatures. The latter effect suggests the formation of regions of possible low-temperature crystallization. It has been established that the HPT causes a significant decrease in the thermal effect of crystallization upon heating of the alloys with a high copper content relative to that of the initial amorphous melt quenched state. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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16 pages, 3412 KiB

Open AccessArticle

The Electrochemical and Mechanical Behavior of Bulk and Porous Superelastic Ti‒Zr-Based Alloys for Biomedical Applications

by Yulia Zhukova, Anastasia Korobkova, Sergey Dubinskiy, Yury Pustov, Anton Konopatsky, Dmitry Podgorny, Mikhail Filonov, Sergey Prokoshkin and Vladimir Brailovski

Materials 2019, 12(15), 2395; https://doi.org/10.3390/ma12152395 - 27 Jul 2019

Cited by 5 | Viewed by 2773

Abstract

Titanium alloys are well recognized as appropriate materials for biomedical implants. These devices are designed to operate in quite aggressive human body media, so it is important to study the corrosion and electrochemical behavior of the novel materials alongside the underlying chemical and [...] Read more.

Titanium alloys are well recognized as appropriate materials for biomedical implants. These devices are designed to operate in quite aggressive human body media, so it is important to study the corrosion and electrochemical behavior of the novel materials alongside the underlying chemical and structural features. In the present study, the prospective Ti‒Zr-based superelastic alloys (Ti-18Zr-14Nb, Ti-18Zr-15Nb, Ti-18Zr-13Nb-1Ta, atom %) were analyzed in terms of their phase composition, functional mechanical properties, the composition and structure of surface oxide films, and the corresponding corrosion and electrochemical behavior in Hanks’ simulated biological solution. The electrochemical parameters of the Ti-18Zr-14Nb material in bulk and foam states were also compared. The results show a significant difference in the functional performance of the studied materials, with different composition and structure states. In particular, the positive effect of the thermomechanical treatment regime, leading to the formation of a favorable microstructure on the corrosion resistance, has been revealed. In general, the Ti-18Zr-15Nb alloy exhibits the optimum combination of functional characteristics in Hanks’ solution, while the Ti-18Zr-13Nb-1Ta alloy shows the highest resistance to the corrosion environment. The Ti-18Zr-14Nb-based foam material exhibits slightly lower passivation kinetics as compared to its bulk equivalent. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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Review

Jump to: Research

24 pages, 9679 KiB

Open AccessFeature PaperReview

Design and Development of Ti–Ni, Ni–Mn–Ga and Cu–Al–Ni-based Alloys with High and Low Temperature Shape Memory Effects

by Vladimir Pushin, Nataliya Kuranova, Elena Marchenkova and Artemy Pushin

Materials 2019, 12(16), 2616; https://doi.org/10.3390/ma12162616 - 16 Aug 2019

Cited by 38 | Viewed by 4722

Abstract

In recent years, multicomponent alloys with shape memory effects (SMEs), based on the ordered intermetallic compounds B2–TiNi, L2₁–Ni₂MnGa, B2– and D0₃–Cu–Me (Me = Al, Ni, Zn), which represent a special important class of intelligent materials, have been [...] Read more.

In recent years, multicomponent alloys with shape memory effects (SMEs), based on the ordered intermetallic compounds B2–TiNi, L2₁–Ni₂MnGa, B2– and D0₃–Cu–Me (Me = Al, Ni, Zn), which represent a special important class of intelligent materials, have been of great interest. However, only a small number of known alloys with SMEs were found to have thermoelastic martensitic transformations (TMTs) at high temperatures. It is also found that most of the materials with TMTs and related SMEs do not have the necessary ductility and this is currently one of the main restrictions of their wide practical application. The aim of the present work is to design and develop multicomponent alloys with TMTs together with ways to improve their strength and ductile properties, using doping and advanced methods of thermal and thermomechanical treatments. The structure, phase composition, and TMTs were investigated by transmission- and scanning electron microscopy, as well as by neutron-, electron- and X-ray diffraction. Temperature measurements of the electrical resistance, magnetic susceptibility, as well as tests of the tensile mechanical properties and special characteristics of SMEs were also used. Temperature–concentration dependences for TMTs in the binary and ternary alloys of a number of quasi-binary systems were determined and discussed. It is shown that the ductility and strength of alloys required for the realization of SMEs can be achieved through optimal alloying, which excludes decomposition in the temperature range of SMEs’ usage, as well as via various treatments that ensure the formation of their fine- (FG) and ultra-fine-grained (UFG) structure. Full article

(This article belongs to the Special Issue Materials with Shape Memory: Phase Transformations, Microstructure and Properties)

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