V. V. Koledov

Melt-spun thin ribbons of shape memory TiNiCu alloy for micromechanical applications

The development of micromechanical devices (MEMS and NEMS) on the basis of nanostructured shape memory alloys is reported. A Ti50Ni25Cu25 (at. %) alloy fabricated by the melt spinning technique in the form of a ribbon with a thickness around 40 μm and a width about 1.5 mm was chosen as a starting material. Technological parameters were optimized to produce the alloy in an amorphous state. The thickness of the ribbon was reduced to 5–14 μm by means of electrochemical polishing. A nanostructural state of the thin ribbons was obtained via the dynamic crystallization of the amorphous alloy by application of a single electric pulse with duration in the range of 300–900 μs. A microtweezers prototype with a composite cantilever of 0.8 μm thick and 8 μm long was developed and produced on the basis of the obtained nanostructured thin ribbons by means of the focused ion beam technique. Controlled deformation of the micromanipulator was achieved by heating using semiconductor laser radiation in a vacuum chamber of scanning ion-probe microscope.

Submicron-sized actuators based on enhanced shape memory composite material fabricated by FIB-CVD

An enhanced scheme for a functional bilayered composite material with shape memory effect has been successfully applied on the microscale to fabricate a thermally controlled microactuator. Fabrication of cantilever-type microactuators from melt spun ribbon of TiNiCu shape memory alloy included electro-chemical polishing followed by focused ion beam milling and ion-assisted chemical vapor deposition of Pt elastic layer. The smallest working microactuator had a volume of 0:9 m 3 . The structure and thermal stability of the Pt layer have been investigated. The fabricated actuator has been proposed for use as micromechanical nanotweezers for manipulation of submicron- and nano-sized objects. Manipulation of a carbon nanotube bunch has been demonstrated. (Some figures may appear in colour only in the online journal)

Actuators based on composite material with shape-memory effect

A new scheme of composite functional material based on an alloy exhibiting a shape-memory effect (SME) is proposed. The scheme provides for a giant reversible bending deformation with the use of only “one-way”-SME alloy. An experiment was performed with the use of actuator models manufactured by gluing together the rapidly quenched ribbons and electroplating the pseudoplastically predeformed ribbons of the alloy with nickel. It is shown that the theoretical estimates of the bending moment developed by the actuator and of the reversible deformations of the actuator are in good agreement with the results of the model experiments. The prospects for the use of the new scheme in micro- and nanomechanics are considered. Actuators with record small overall dimensions have been manufactured by the focused ion-beam technique.

Phase transitions in intermetallic compounds Ni-Mn-Ga with shape memory effect

The effect of a magnetic field on the formation of structural domains at martensitic transition in the intermetallic system Ni/sub 2+x/Mn/sub 1-x/Ga was studied. For the compositions x whose temperatures of structural and magnetic transitions are close this effect is most pronounced. In the field of 0.2 to 1 T the increase in the transition temperature is linear with the coefficient of 0.015 K/T. Estimates of the transition temperature shift based on thermodynamic calculations are in good agreement with the experimental data. It is shown that the switching on the magnetic field at some critical temperature induces partial transformation of austenite into martensite.

Shape Memory Effect in Microsized Samples of Rapidly Quenched Ferromagnetic Alloy Ni-Mn-Ga

The melt spun ribbons of ferromagnetic shape-memory alloy (FSMA) Ni53Mn24Ga23 have been prepared by rapid quenching. Thermomechanical properties have been studied by multi-point technique and perfect shape memory effect (SME) observed. The magnetic field effect on thermomechanical behavior was studied by placing multi-point press into Bitter magnet. A giant (1.2%) bending strain, due to magnetic field-induced martensitic transformation (magnetic-field-induced SME), has been observed at a constant temperature T= 56 °C in a field of 6 T. At least 80% of martensitic transformation reversibly induced by the external field was observed experimentally. Submicron sized samples of the alloy with thicknesses down to 300 nm have been milled by focused ion beam (FIB) technique. The deformation behavior of these samples was studied by Omniprobe micromanipulator in the vacuum chamber of FIB device. The SME response was tested in situ by heating the samples with a semiconductor laser. Strong two-way SME was observed due to bending strains of the samples under study.

New Heusler alloys with a metamagnetostructural phase transition

Investigations of new ferromagnetic shape-memory Ni-Mn-Z Heusler alloys (Z = In, Sn, Sb) are reviewed. Experimental data are described and explained on the assumption that these alloys undergo a phase transition from the ferromagnetic to the antiferromagnetic state (metamagnetic transition). The results of theoretical studies of the phase diagrams of these alloys are considered with regard to the possible change in the character of magnetic ordering (from ferromagnetic to antiferromagnetic) and interaction of the structural martensitic transformation with the metamagnetic transition.

Field Dependence of the Magnetocaloric Effect in MnFe(P,Si) Materials

The field dependence of the magnetocaloric effect (MCE) in Mn_1.22Fe_0.73P_0.47Si_0.53 is studied in terms of the entropy change (ΔS) and the temperature change (ΔT) for applied magnetic fields up to 5 and 14 T, respectively. The magnetic fields required to saturate the MCE in this system are ~1.7 and 4-5 T for ΔS and ΔT, respectively. The MCE field dependence is compared with the two approaches of the literature: 1) latent heat model and 2) the power law evolution predicted from the universal analysis of the MCE. It turns out that both of these methods are unsuitable to describe the MCE field evolution in MnFe(P,Si) materials.

Magnetic, thermal, and electrical properties of an Ni45.37Mn40.91In13.72 Heusler alloy

The magnetization, the electrical resistivity, the specific heat, the thermal conductivity, and the thermal diffusion of a polycrystalline Heusler alloy Ni45.37Mn40.91In13.72 sample are studied. Anomalies, which are related to the coexistence of martensite and austenite phases and the change in their ratio induced by a magnetic field and temperature, are revealed and interpreted. The behavior of the properties of the alloy near Curie temperature TC also demonstrates signs of a structural transition, which suggests that the detected transition is a first-order magnetostructural phase transition. The nontrivial behavior of specific heat detected near the martensite transformation temperatures is partly related to a change in the electron density of states near the Fermi level. The peculiar peak of phonon thermal conductivity near the martensitic transformation is interpreted as a consequence of the appearance of additional soft phonon modes, which contribute to the specific heat and the thermal conductivity.

Magnetic Field and Annealing Influence on the Martensitic Transition in Ni45.8Mn42.6In11.6 Shape Memory Alloy Ribbons

We report the effect of shorttime vacuum annealing, during 10 minutes at 923 K, 973 K, 1023 K and 1073 K, on magnetostructural properties of as-quenched ribbons of Ni45.5Mn43In11.5 Heusler alloy. The martensitic transformation is strongly sensitive to annealing treatments. The martensitic phase starting temperature is significantly shifted from 239 K towards higher temperatures around 370 K. It suffers a break down in two peaks when a field equal or higher than 500 Oe is applied to the as-quenched sample. This effect is not detected in the transformation of annealed ribbons but its signature can be observed at low temperature. Moreover, under high magnetic field up to 30 kOe temperatures associated with both martensitic and reverse transitions do not change for annealed samples, meanwhile the magnetization difference between austenite and martensite increases with the field. Nevertheless, it almost remains unchanged in the as-quenched ribbon.

Structure and functional properties of rapidly quenched ribbons of Ti2NiCu alloy with different fractions of the crystalline phase

The controllable annealing of amorphous Ti2NiCu ribbons by a pulsed electric current was developed, and samples with different fractions of crystalline phase were obtained. The samples’ structure was studied using high-resolution electron microscopy. Annealing conditions allowing us to obtain an amorphous nanocrystalline structure with grain sizes of less than 10 nm were determined. Conditions for obtaining samples with the two-wave shape memory effect were found. A prototype micromanipulator was designed and successfully tested.