Layered amorphous-crystalline TiNiCu alloy ribbons produced by ultrarapid quenching from the liquid state (melt spinning technique) show the two-way shape memory effect without additional processing, which makes them applicable to various micromechanical devices (microtweezers) for gripping and manipulating microobjects. The present work is devoted to the study of the influence of the rejuvenation process (cryogenic thermal cycling) and the thickness of the crystalline layer on the structure and functional properties of quasi-binary TiNi-TiCu alloy with the copper content 25 at

Rapidly quenched thin TiNiCu alloy ribbons are precursors in the fabrication of micro- and nanotweezers for the manipulation of micro- and nanoscale objects. The thickness of the ribbons has been reduced by cold rolling in amorphous state. A thickness reduction rate of 1.2-1.5 times has been achieved by rolling with a load of up to 12 tons. We show that shape memory effect has been generated after isothermal crystallization in the rolled ribbons. The characteristic martensitic transformation temperatures have increased, the transformation hysteresis width has decreased and the shape memory effect has decreased slightly. The lateral roughness of the ribbon surfaces has decreased both for the contact and the reverse ribbon surfaces.

The B2 F iota B19 ' martensitic transformation was studied on thermal cycling of the Ti40.7Hf9.5Ni49.8-xCux (x = 5, 10 at.%) thin ribbons. The temperatures, as well as the enthalpy of the transformation, were found to be stable on thermal cycling. The stability of the B2 F iota B19 ' transformation was attributed to the formation of a specific grain structure during the crystallization of the initially amorphous ribbons. The grains were characterized by an average size of 800 nm, which increased the yield limit for dislocation slip to 700 MPa. Moreover, one martensite corresponding variant pair (CVP) formed on cooling inside each grain. It was assumed that the formation of one CVP martensite plate within the grain on cooling, as well as a high yield limit for dislocation slip, might have been responsible for the stability of the martensitic transformation temperatures and enthalpy on thermal cycling.

Layered amorphous-crystalline ribbons of rapidly quenched TiNiCu alloy with two-way shape memory effect (TWSME) have proven to be a promising material for microtweezers used for the gripping and manipulation of micro- and nanoscale objects. Ribbons with different crystalline layer thicknesses have been produced in this work by melt spinning at variable melt cooling rate. A method has been proposed and an innovative experimental setup has been designed for TWSME studies. We show that reducing the melt cooling rate one can increase the thickness of the crystalline layer, accompanied by an increase in the minimum ribbon bending radius and the maximum reversible deformation during the implementation of the TWSME. The test ribbon samples have been rejuvenation treated (cryogenic thermocycling). It has been shown that cryothermal treatment can tangibly increase the TWSME reversible deformation and significantly reduce the width of the shape change temperature hysteresis. The latter effect can be used for improving the performance of microdevices, in particular microtweezers, based on rapidly quenched amorphous-crystalline ribbons.

The study of TiNiCu alloy samples in the initial state after quenching by EXAFS revealed the dependence of the local atomic structure of the alloys on the copper content. Studies of the structure of alloys by X-ray diffraction (XRD) using synchrotron radiation with a wavelength of 0.8 Å showed that in the initial state after quenching, the alloys are in an amorphous state. After isothermal crystallization of alloys at a temperature of 500° C for 300 s, it was found that samples of alloys with a copper content of more than 30 at.% after crystallization became so brittle that they were unsuitable for further research. This is a consequence of the peculiarities of the local atomic structure of the alloys identified by the EXAFS method. Temperature intervals and the nature of alloy phase martensitic transformations (MT) were determined by differential scanning calorimetry (DSC).

Insect pest control requires fundamental knowledge of their physiology and behavioral responses. However, due to the small size of insects in general and their sensory organs (sensilla), in particular, the study of the physiology of insect sensory systems has until recently been limited by insufficient accuracy and selectivity of experimental mechanical action. To eliminate this gap in the study of insects nervous system, a microrobotic technology is proposed based on a micromechanical device - microtweezers based on a layered structural composite of $\text{Ti}_{50} \text{Ni}_{25} \text{Cu}_{25}$ alloy with a shape memory effect (SME), combined with a temperature control system and a three-coordinate piezoelectric micropositioner. Microtweezers with SME selectively capture the smallest sensilla of the studied insects, enabling their precise mechanical stimulation with simultaneous recording of physiological responses generated by sensilla by methods of electric impulse derivation in the nerve centers of the insect.

The local crystalline environment of Ni and Cu atoms in the quasi-binary TiNi-TiCu shape memory alloys containing 30 and 40 at.% Cu has been studied using EXAFS spectroscopy. Amorphous melt-spun alloy ribbons have been crystallized by isothermal annealing or by exposing to a short (10 ms) electric pulse. Analysis of the EXAFS spectra has shown that electropulse crystallization has a more noticeable effect on the local atomic structure of austenite compared to martensite. In particular, it leads to a decrease in the local disorder of atoms in the Cu coordination shells, a decrease in the lengths of Cu-Ni and Cu-Cu bonds, hinders an increase in the lattice parameter of the austenite phase and stabilizes its crystal structure. The observed changes in the local atomic structure of the austenite phase of the alloys contribute to the improvement in the shape memory properties.

The aim of the present paper was to study the strain variation in the NiTi-based shape memory alloys during isothermal holding under stress. The recoverable strain of Ni51Ti49 and Ti40.7Hf9.5Ni44.8Cu5 alloys was studied on holding under stress after cooling (Regime 1), after active loading (Regime 2), or during holding without stress in the sample that demonstrates the two-way shape memory effect (Regime 3). The strain variation was found during holding under a stress in all regimes. This strain was recovered on subsequent heating or unloading, thus, the strain variation on holding was caused by the isothermal martensitic transformation. This isothermal strain depended on the chemical composition of the alloy, the regime for the isothermal holding, the stress, and the holding temperature. The maximum isothermal strain was 3.4% in Ti40.7Hf9.5Ni44.8Cu5 (Regime 1) and 6.1% in Ni51Ti49 (Regime 2). Holding in Regime 3 was accompanied by a small strain (less than 0.3%). The influence of the stored elastic energy on isothermal martensitic transformation on holding was discussed, and it was shown that a large isothermal strain was found if the transformation was accompanied by a small stored elastic energy.

Alloys of the quasibinary TiNi-TiCu system manufactured by melt quenching in the form of thin 20–50 μm ribbons have proven to show good potential as materials for the fabrication of micromechanical devices. At high cooling rates (about 106 K/s), this method allows producing high-copper (more than 20 at.%) amorphous alloys which exhibit an excellent shape-memory effect after crystallization. Their properties are known to largely depend on the crystallization conditions and the structure of the initial amorphous material acting as a precursor for the formation of crystal phases. It has been shown recently that the rejuvenation procedure (cryogenic thermocycling) of metallic glasses is one of the most promising methods of improving their properties. In this study, we investigated for the first time the effect of cryogenic thermocycling of rapidly quenched amorphous TiNiCu on the initial state, as well as on structure formation and the phase transformation patterns of subsequent crystallization conducted using various methods. The effect was analyzed utilizing the methods of scanning and transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry. The results show that rejuvenation treatment slightly reduces the glass transition and crystallization onset temperatures and moderately changes the sizes of structural features (grains, martensite plates), the quantity of the martensite phase, and the characteristic temperatures and enthalpy of the martensitic transformation.

Strain variation on holding under a constant stress was studied in the Ti40,7Hf9,5Ni41,8Cu8 alloy. It was found, that on holding under stress, the isothermal strain rose up to saturation, which value depended on holding temperature and stress. It was found that the dependencies of the isothermal strain on the holding temperature and stress were non-monotonic. This allowed to find the optimal value of stress and time at which the isothermal strain attained the maximum value of 3.2 %. It was found that the maximum isothermal strain in the Ti40,7Hf9,5Ni41,8Cu8 alloy was less than in the Ti40,7Hf9,5Ni44,8Cu5 alloy.

The study of the effect of electropulse treatment with a variable duration on the crystallization processes and the structure of a amorphous TiNiCu alloy with 25 at.% Cu in comparison with isothermal annealing and heating at a constant speed was carried out. The alloy was fabricated by rapid-quenching from the liquid state (melt spinning technique) at the cooling rate of the melt of about 10 6 °C/s in the form of a ribbon with a thickness of 28 μm with a surface crystal layer with a thickness of about 2-3 μm. To remove the crystal layer, the method of double-sided electrochemical polishing was used. The studies were carried out by methods of differential scanning calorimetry, metallography and scanning electron microscopy. It was established that the formation of the crystalline phase in the electropulse treatment of the amorphous ribbon occurs from the surface to the inner part due to the predominant formation and growth of columnar crystals with subsequent nucleation and growth of crystals in the rest of the ribbon.

The aim of this paper was to study the isothermal forward martensitic transformation in binary, ternary, and quaternary NiTi-based shape memory alloys to find the origin of this phenomenon. The results obtained showed that the isothermal B2-* B19 ' transformation was observed only in the NiTi-based alloys with substitutional defects. The critical concentration of copper was found that completely suppressed the martensitic transformation both on cooling or isothermal holding in Ti-Hf-Ni-Cu alloys. The thermodynamics of the martensitic transformation that occurred in the presence or absence of the substitutional defects was discussed, and the reason for the influence of the substitutional defects on the martensitic transformation was clarified. It was verified that the formation of the martensite phase on isothermal holding was caused by the local fluctuation of the substitutional defect concentration which led to fulfilment of the thermodynamic condition for the martensitic transformation. It was shown that the maximum volume fraction of the isothermal martensite was limited by the maximum volume of martensite that corresponded to the thermal elastic equilibrium and appeared on cooling of the alloy without substitutional defects. The results allowed to conclude that the martensitic transformation remained to be thermal elastic in the NiTi-based alloys with a non-stoichiometric composition however, the martensite nucleation was controlled by the thermally activated migration of substitutional defects. (c) 2021 Elsevier B.V. All rights reserved.

Rapidly quenched thin ribbons of quasi-binary TiNi–TiCu system alloys with high copper contents (more than 20 at.%) are promising materials for the manufacture microactuators due to excellent shape memory effect with narrow temperature hysteresis. Amorphous TiNiCu alloys with a copper content of 30–40 at.% were obtained by the melt spinning technique at a melt cooling rate of 106 K/s in the form of ribbons with a thickness of about $40\ \mu\mathrm{m}$. The crystallization of the alloys was carried out using electropulse treatment with duration in the range from 5 to 1000 ms. X-ray diffraction studies showed that at room temperature all alloys exhibit B19 martensitic structure. Microstructure of the ribbons consists of columnar crystals near the ribbon surfaces and large grains with characteristic sizes from 3 to $12\ \mu\mathrm{m}$. TEM examination revealed a subgrain structure with nanoscale martensite plates (20-80 nm). The alloys exhibit one-stage martensitic transformation $\mathrm{B}2\leftrightarrow \mathrm{B}19$ and pronounced shape memory effect in the temperature range of 55-75°C.

An excimer KrF laser and specially developed modes of irradiation are used to achieve different degrees of crystallization for the surfaces and volumes of melt-quenched ribbons of cobalt- and iron-based amorphous alloy. The effect the geometry and parameters of laser irradiation have on the mechanical behavior of the studied amorphous alloy and amorphous–crystalline composites is studied relative to the evolution of their structure.

TiNi-TiCu quasibinary system alloys with a high Cu content produced by rapid quenching from liquid state in the form of thin amorphous ribbons exhibit pronounced shape memory effect after crystallization and are promising materials for miniaturized and fast operating devices. There is currently no complete clarity of the mechanisms of structure formation during crystallization from the amorphous state that determine the structure-sensitive properties of these alloys. This work deals with the effect of the initial amorphous state structure and crystallization method of the alloys on their structure and phase transformations. To this end the alloy containing 30 at.% Cu was subjected to thermal and mechanical impact in the amorphous state and crystallized using isothermal or electropulse treatment. We show that after all types of treatment in the amorphous state the structure of the alloy remains almost completely amorphous but the characteristic temperatures and enthalpy of crystallization become slightly lower. Isothermal crystallization of alloy specimens produces a submicrocrystalline structure with an average grain size in the 0.4–1.0 μm range whereas electropulse crystallization generates a bimorphic structure consisting of large 4–6 μm grains and 2–3 μm high columnar crystals in the vicinity of the surface. The grains have nanosized plate-like and subgrain structures. The largest grains are observed in thermally activated samples, meanwhile, mechanical impact in the amorphous state leads to the formation of equiaxed finer grains with a less defective subgrain structure and to the shift of the temperature range of the martensitic transformation toward lower temperatures.

The efficiency of shape memory alloys for the MEMS technology has been recently demonstrated. Quasibinary intermetallic TiNi-TiCu alloys produced by rapid quenching from liquid phase in the form of thin (about 40 um) ribbons are an attractive material for the fabrication of micro-actuators due to their narrow temperature hysteresis of the shape memory effect (SME) and relatively large recoverable strain. In order to broaden the functionality of SME microdevices, in this work we have alloyed TiNiCu containing 25 at.% copper with aluminum. The results have shown that alloying with 0.6 at.% Al increases the cast characteristics of the composition and favors its amorphization. Upon crystallization by isothermal annealing or electropulse treatment the resultant microstructure and SME properties of the Al containing alloy change but slightly in comparison with the original alloy however there is a significant shift (by more than 15°C) of the SME temperature range toward lower temperatures.

Amorphous-crystalline alloy of the TiNi–TiCu quasi-binary system with 25 at.% copper content is prepared in the form of thin ribbons by rapid quenching from a liquid state. Completely amorphous ribbons are obtained using electrochemical polishing. It is shown that the crystal structure prepared by high-speed electropulsing heat treatment differ significantly from that prepared by isothermal heat treatment. The initial ribbon crystallizes as column-like crystals growing from both surfaces of the ribbon and as large lens-like crystals in the volume of the ribbon. The structure of column-like crystals reproduces the morphology and texture of the original crystalline layer. Reducing the electropulsing time to 1 ms increases the fraction of column-like crystals while their height increases and the width decreases. After the amorphous ribbon is crystallized, the structures of column-like crystals on both surfaces have similar crystallographic orientations.

Amorphous ribbons from a rapidly quenched alloy of the TiNi–TiCu quasi-binary system with copper content of 30 at % are crystallized via electric pulse treatment with variable durations of impact in the range of 1 to 100 ms at external tensile stress of up to 250 MPa. It is shown that the formed bimorph structure of columnar and coarse crystals is characterized by considerable differences when compared to a rapidly quenched alloy with 25 at % copper. An increase in tensile stress does not affect the phase composition or microstructure of the alloy, but it does lower the critical temperatures of martensitic transformation.

ZnO nanowires are recognized as prospective active material for highly sensitive biological or gas sensors. The objective of the work is the experimental development of the technology of 3D nanomanipulation and nanoassemling of the sensing nanostructures using ZnO nanowires. The 50 nm thick and $3\ -5\ \ \mu\mathrm{m}$ long ZnO nanowires with hexagonal wurtzite structure were prepared by hydrothermal method. The system for nanomanipulation of the individual nanowires in SEM included Kleiniek nanomanipulator equipped with Ti 2 NiCu composite nanotweezers with shape memory effect. The necessary parameters of the nanotweezers are discussed and the characteristics of the nanomanipulation and nano-assembly procedure are considered.

Present work considers the study of sensilla, which are sensitive elements of insect sensory systems. Sensilla are believed to be efficient nanobiosensors, the subtle mechanisms of operation of which have not been sufficiently studied. Different types of sensilla allow the insect to receive mechanical stimuli (air currents, sound, touch). To study mechanosensory sensilla, a micromechanical instrument is needed that would allow the capture of sensilla and its deflection in a predetermined manner. The paper proposes a method for recording the activity of a mechanosensory neuron during inactivation of individual sensilla by means of microtweezers based on the shape memory effect.