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The effect of iron addition on the martensitic transformation (MT) and shape memory effect (SME) of the Ni 2 MnGa sputtered films was investigated. It was found that the constraint-aged films with more than 8.5 mol% Fe have two phases. MT temperatures monotonously decreased with increasing amount of iron addition, while the Curie temperature increased. The reversible two-way SME by the thermal change was confirmed for all constraint-aged films containing iron through the MT and its reversion. Furthermore, the SME by magnetic field was observed around the MT temperature on cooling for the films containing iron in which MT occurred within the ferromagnetic region. The strain change in a low magnetic field of 1 T became large for the films containing iron. The behavior is as expected from the MT induced by the low magnetic field.

The effect of iron and cobalt addition on the magnetic and shape memory properties of Ni 2 MnGa sputtered films was investigated. It was found that heat-treated films with more than 5.1 mol% Co have two phases. Martensitic transformation temperatures of the constraint-aged films decreased with the iron addition and increased with increasing cobalt content. The Curie temperature of the heat-treated films increased with increasing amount of iron or cobalt. The constraint-aged films containing iron and cobalt exhibited a two-way shape memory effect by heating and cooling.

The shape memory effect (SME) induced by the magnetic field is interesting and important for physics and application. The ferromagnetic Ni 2 MnGa films with various compositions were deposited on a poly-vinyl alcohol (PVA) substrate with a radio-frequency (RF) magnetron sputtering apparatus using four kinds of Ni-Mn-Ga targets. After separating from the substrate, the films were heat-treated at 1073 K for 3.6 ks for homogenization and aged at 673 K for 3.6 ks in a constraint condition. The reversible two-way SME by the thermal change was confirmed for the constraint-aged films with various compositions. The gradient of the strain-temperature curve, the amount of strain accompanied by the two-way SME and the width of thermal hysteresis were dependent on the composition of the films. The strain-temperature curve shifted to a high temperature region and the martensitic phase was stabilized by the applied magnetic field. Furthermore, the two-way SME by the magnetic field was observed around the martensitic transformation temperature on cooling for the constraint-aged film, which showed the large gradient and small thermal hysteresis in the strain-temperature curve.

The martensitic phase transition in Ni2MnGa related alloys is investigated. The stability of the low temperature phase is assessed by a structural investigation of a cold worked sample. The stability of the low temperature martensitic phase with respect to internal strains is determined. It is argued that the experimental observations are consistent with an electronic mechanism being responsible for causing the martensitic phase transition. Alloying experiments with partial substitution of Ga by either In or Sn show a stronger dependence of the martensitic phase transition on the number of conduction electrons than on the size of atoms or variations of their distances. These experimental findings are consistent with band structure calculations and changes brought about by atomic disorder.

The shape memory effect (SME) by magnetic field is interesting and important for physics and application. The Ni2MnGa films were deposited on a poly-vinyl alcohol (PVA) substrate with a radio-frequency (RF) magnetron sputtering apparatus using Ni52Mn24Ga24 or Ni52.5Mn22Ga25.5 target. After separating from the substrate, the films were heat-treated at 1073 K for 36 ks for homogenization and ordering. They were constrained in a silica tube and heated at 673 K for 14.4 and 57.6 ks. The two-way SME for each constraint-aged film was confirmed by thermal cycling. The shape change of film under magnetic field was observed at constant temperature between A s ∗ and A f ∗ , or M s ∗ and M f ∗ . Magnetic field was applied parallel to the film surface up to 5 T using a super-conductor magnet. These films showed the SME by magnetic field. The strain by magnetic field was dependent on the measurement temperature. At temperatures between M s ∗ and M f ∗ , the strain increased with increasing magnetic field and slightly decreased with decreasing magnetic field. The martensitic transformation was induced by the magnetic field up to 5 T, which corresponds to that observed by cooling down to about 4 K.

The martensitic phase transition in Ni2MnGa, fundamental to its shape memory behaviour, can be described by two successive 110 type shears leading to 36 possible different orientations for the axes of the pseudo-tetragonal martensitic phase. The distribution and orientation of the domains formed on cooling Ni2MnGa into the martensitic phase has been studied using single-crystal neutron diffraction with a multi-detector. The number of domains actually occurring was rather low and was reduced by residual strain. Thermal cycling through the phase transition was found to further reduce the number of domains occurring, which may stabilize after several cycles. Uniaxial stress or a magnetic field applied parallel to [001] is able to switch domains whose pseudo-tetragonal axis is [100] or [010] to ones of type [001]. The results suggest that plastic deformation in the martensitic phase takes place by twinning (change of domain), rather than by slip and that the shape memory property arises from the fixed orientation relationship between the martensitic twins and the high temperature cubic axes.

The shape memory behavior under the magnetic field up to 5 T was observed in Ni-Mn-Ga sputtered films. The sputtered films were heattreated at 1073 K for 36 ks for homogenization and aged at 673 K for 14.4 and 56.7 ks in a constraint condition. The martensitic transformation temperatures and Curie temperature of the obtained films were higher than room temperature. The martensitic transformation temperatures increased under a magnetic field. Furthermore, a shape memory effect was observed by increasing and decreasing of the magnetic field.

Ni2MnGa alloy is an intelligent material with ferromagnetic and shape memory properties. The application of the alloy films to micro-actuators has been proposed. The Ni-rich Ni2MnGa alloy films with a thickness of nearly 5 \\micron were deposited on Al2O3 substrates by a radio-frequency magnetron sputtering apparatus using a Ni52Mn24Ga24 target. They were heat-treated at 1073 K for 36 ks for homogenization and ordering. The martensitic transformation temperatures of the heat-treated films were higher than room temperature. To investigate the effect of aging time on shape memory properties, the heat-treated films were aged at 673 K for various times between 0.9 and 57.6 ks in a constrained condition. The constraint-aged films showed the two-way shape memory effect by thermal cycling. Fine precipitates with a crystal structure of L12 were observed in the constraint-films aged for a long period. As for their two-way shape memory properties, a range of transformation temperature narrowed and the amount of macroscopic shape change increased with increasing aging time.

Phenomenological modeling on the thermomechanical behavior of shape memory alloy (SMA) plates with two-way shape memory effect (TWSME) is presented in this paper. Two important characteristics of SMA materials as sensors or actuators; the thermal responses and the transformation accompanied deformation; are described by the proposed models. The latent heat effect during transformation is approximately expressed by an apparent specific heat as a function of transformation temperatures. The transformation-induced deformation of SMA plates is described by newly defined transformation expansion coefficients, based on the physical understanding of the mechanism of TWSME. The proposed model is verified by the comparison between numerical simulation and experiments on the thermomechanical behavior of SMA plates.

The intermetallic compound Ni2MnGa has a shape memory effect and a ferromagnetic property. Films of this compound may be applied for an actuator of micro-machines. The Ni-rich Ni2MnGa films with a nearly 5 μm thickness were deposited on an Al 2 O 3 substrate by a radio-frequency magnetron sputtering apparatus with a Ni 52 Mn 24 Ga 24 target. The sputtering power was 400 W and the substrate temperature was kept at 323 K by cooling water. The composition of the deposited films was Ni-23.4 mol%Mn-23.0 mol%Ga. They were annealed at 1073 K for 36 ks for homogenization and ordering, and slowly cooled down in the furnace. Martensitic transformation temperatures of the films were measured by a differential scanning calorimeter, and the results were M s = 315 K, M f = 311 K, As = 316 K and A f = 321 K. To induce a shape memory effect, the annealed films were aged at 573-773 K for 0.9-3.6 ks in a constrained condition. It was found that they showed the two-way shape memory effect by thermal cycling.

Effect of adding cobalt on the shape memory properties of Ni-Mn-Ga sputtered films was investigated. It was found that the films containing cobalt less than 5.1 mol% has a single phase and those with more than 6.8 mol%Co has two phases. The Curie temperature increased and the saturation magnetization decreased with increasing cobalt content. These films exhibited one way shape memory effect. The shape recovery start temperature increased and the temperature range of shape change broadened with increasing cobalt content.

The fatigue test device of Shape Memory Alloy wire was developed using the Peltier element of Bi2Te3 and Sb2Te3 for p type and Bi3Te3 and Sb2Se3 for n type. The measurements of Ti-Ni-Cu wire and rapidly solidified Ti-Ni and Ti-Ni-Cu were carried out by short cycle time of heating and cooling under stable temperature control. From the experiment, it was concluded that the elongation by plastic deformation caused the fatigue and degradation of Shape Memory Alloy.

Several properties with a thermoelastic phase transformation, the so-called shape memory effect, were studied in rapidly quenchd melt-spun Ti50Ni50−xCux (x = 0–20 at.%). By taking account of the improvements in several characteristics such as the large ductility (i.e. 180° bending ability), narrow transformation temperature range δT( = Af − Mf) and high thermal energy conversion ability ν, it can be concluded that the merit and functional superiority of rapidly quenched melt-spun TiNiCu ribbon exist especially in the range of copper contents over 10 at.% in comparison with the conventionally manufactured (i.e. melting-mechanically worked) material.

The actuator of Shape Memory Alloy coil with bias spring was developed and its precision was investigated. This device was operated by electrical heating on the Pulse Width Modulation method using computer in oder to make high precision of position control. The position was measured by electric micrometer. This was made under the conceptof the stage which was used in semiconductor production lines and so on for the reason of the cleanness of this actuator.

Differential scanning calorimetry (DSC) and magnetic measurements were performed to study the influence of ferromagnetic 3-d transition elements Fe and Co on structural and magnetic properties of ferromagnetic shape memory alloys Ni2MnGa. Addition of Fe or Co on the Ni sites decreases the temperature of martensitic phase transition Tm, whereas addition of Co on the Mn sites results in a considerable increase of Tm. Magnetic measurement revealed that Curie temperature TC increases upon substitution of Fe or Co for Ni. This observation is of importance for design of high temperature ferromagnetic shape memory alloys., 4 pages, 3 figures

Mechanical and shape memory properties of a polycrystalline Ni2.18Mn0.82Ga alloy prepared by a PDS (Pulse Discharge Sintering) method were investigated. It was found that the material demonstrates the two-way shape memory effect after a loading - unloading cycle performed in the martensitic state, i. e. essentially without special training. The samples exhibiting the two-way shape memory effect show a significant enhancement in the magnitude of magnetic-field-induced strain., 4 pages, 5 figures, REVTEX-4

The magnetic properties of Ni2+xMn1-xGa (x=0.05, 0.1, 0.13, 0.14, 0.16, 0.17, 0.18, 0.19 and 0.2) shape memory alloys were measured in the temperature range from 130K up to 520K. For the composition with x=0.18 the Curie temperature and magnetization of saturation have a minimum. Besides thermal hysteresis of magnetization was found.

Mesure de la force de restauration lors de la transformation martensitique thermoelastique accompagnant une variation de temperature dans les plaques d'alliage Ni-49 et 50% at Ti. Influence de la geometrie de l'echantillon (forme et longueur)

Heusler type Ni2MnGa is a ferromagnetic shape memory alloy. Martensitic transformation occurs within the ferromagnetic temperature range. Ni2MnGa films were fabricated by the melt spinning method and the sputtering method. The physical properties, such as transformatio n temperatures and magnetic behaviors, of these films was studied. These films had good crystallinity with preferred orientation and showed the crystal structure as same as bulk specimen. Rapidly solidified Ni2MnGa films made by the single roll melt spinning method have 20um in thickness and lmm in width. Sputtered Ni2MnGa films were made by using a high frequency magnetron sputtering apparatus. The thickness of the film was 5um. The films which were deposited on the poly-vinyl alcohol substrate showed shape memory effect.