Martensitic Transformation and Shape Memory Effect in NiTi/PPX-C Composites Dedicated to Medical Applications

Influence of al concentration on deformation behavior and fracture mode of fe-30mn-6(SI, AL) alloys

The shape memory effect is now generally known as the phenomenon that a specimen apparently plastically deformed at some lower temperature reverts to its undeformed original shape on heating to a somewhat higher temperature in virtue of the reverse martensitic transformation. This phenomenon is very peculiar compared to the ordinary plastic deformation behaviour. Thus, it has been of great interest for many workers of both academic and technological fields, and is now found in a lot of alloy systems as recently tabulated by Wayman and Shimizu (1) and Delaey et al. (2). A common property for all of the alloy system is that each alloy exhibits a martensitic transformation, and the shape memory effect is commonly observed when the alloy is deformed at a partly or wholly martensitic condition and then heated to the matrix phase (3, 4, 5). These common property and observation indicate that the shape memory effect is originated in the behaviour of materials upon martensitic transformation, deformation of the martensite and reverse transformation to the matrix phase. Therefore, in order to know the mechanism of the shape memory effect, the trans-formations and deformation characteristics must be clarified for alloy systems exhibiting the effect. In this paper, the term “marmem” (1) will be used as descriptive of the shape memory behaviour, since the martensite phase exhibits a memory except for the special case known as the two-way (2) or reversible (6) shape memory effect.

Shape memory effects in [001] Ni55Fe18Ga27 single crystal

Martensitic transformation in stoichiometric NiMn and Ni–Mn-X alloys: A first principles study

Some results concerning the hydrogen effect at electrolytic saturation at a current density of j = 1500 and 3500 A/m2 for 3 h at room temperature on the temperature dependence of the yield stress σ0.1(T) and the shape memory effect (SME) under tension of the [011]-oriented Ti-50.55%Ni (at.%) alloy single crystals are presented. It was shown that hydrogen is in a solid solution and forms particles of titanium hydride TiH2 after hydrogenation at j = 1500 and 3500 A/m2, respectively. Both hydrogen in the solid solution and TiH2 particles led to a decrease in the Ms temperature of the onset of the forward martensitic transformation (MT) upon cooling and the Md temperature (Md is the temperature at which the stresses for the onset of the stress-induced MT are equal to the stresses for the onset of plastic flow of the high-temperature B2 phase), and increased the yield stress σ0.1 of the B2 phase at the Md temperature compared to hydrogen-free crystals. It was found that the SME under stress depends on the tensile stress level and current density. The maximum SME εSME = 10 ± 0.2% at σex = 200 MPa and εSME = 10.5 ± 0.2% at σex = 300 MPa was observed in the hydrogen-free crystals and after hydrogenation at j = 1500 A/m2, respectively, which exceeded the theoretical value of lattice deformation ε0 = 8.95% for the B2-B19′ MT in [011] orientation under tension. At j = 1500 A/m2, the physical reason for the excess of the SME of the theoretical ε0 value was due to the increase in the plasticity of B19′ martensite upon hydrogenation. At j = 3500 A/m2, εSME = 8.0 ± 0.2%, and it was less than ε0 = 8.95% for B2-B19′ MT in [011] orientation under tension. The decrease in SME after hydrogenation at j = 3500 A/m2 was associated with the interaction of two types of B19′-martensite: oriented under stress and non-oriented, formed near TiH2 particles. It was shown that the redistribution of hydrogen in the bulk of the crystals during long-term holding for 168 h at 263 K after hydrogenation at j = 1500 A/m2 increases the SME relative to crystals without long-term holding: 3.5 times at 50 MPa and 1.8 times at 100–150 MPa. After long-term holding, εSME = 9.5 ± 0.2% at 150 MPa, which exceeds the theoretical value ε0 = 8.95% for B2-B19′ MT in [011] orientation under tension.

Shape memory effect in metallic glasses

Martensitic transformation and shape memory effect in ausaged Fe–Ni–Si–Co alloys

The magnetostructural phase transformation and shape memory effect (SME) of Fe-added Ni2MnGa films were investigated. The free-standing films were heat-treated at 1073 K for 3.6 ks and constraint-aged (CA) at various conditions (473 ~ 723 K, 0 ~ 14.4 ks) to make the two-way SME. The reversible two-way SME by the temperature change was confirmed through the martensitic transformation (MT) and its reversion. The gradient of strain-temperature curve, the effective recovery strain and the width of thermal hysteresis were dependent on the CA conditions. The magnetic field (MF) induced structural phase transformation was evaluated by an XRD apparatus in high MF up to 5 T. It was confirmed that the martensitic phase was stabilized by the MF. Furthermore, the SME by the MF was observed around MT temperature on cooling process for the CA film. It was concluded that the MF induced SME appeared by the induction of the MT with MF.

Microstructure, martensitic transformation and shape memory effect of Ni38Co12Mn41In9 alloy

Using single crystals of a Fe – 28% Ni – 17% Co – 11.5% Al – 25% Ta (аt.%) alloy, oriented for tensile loading along the [001] direction, the shape-memory (SME) and superelasticity (SE) effects caused by reversible thermoelastic martensitic transformations (MTs) from a high-temperature fcc-phase into a bctmartensite are investigated. It is demonstrated that the conditions necessary for the thermoelastic MTs to occur are achieved by aging at 973 K within the time interval (t) from 0.5 to 7.0 hours, which is accompanied by precipitation of the γ′-phase particles, (FeNiCo)3(AlTa), whose d < 8–12 nm. When the size of the γ′-precipitates becomes as large as d ≥ 8–12 nm, the MT becomes partially reversible. The physical causes underlying the kinetics of thermoelstic reversible fcc-bct MTs are discussed.

Shape memory effect and related phenomena in a microalloyed FeMnSi alloy

Whole martensitic transformation process in Fe–Mn–Si–Cr shape memory alloy by improved characterization of volume resistivity

A brief overview of the production and application of materials with shape memory effect is given. Data are given, the emergence of such a concept as the shape memory effect in general, as well as data on the first studies of materials with a shape memory effect (SME), data indicating the absence of hardening of the process of accumulation of deformations of direct martensitic transformation in shape memory alloys. It is told about the occurrence of internal stresses, tending to return the structure to its original state. The advantages and uniqueness of these alloys are shown. The shape memory effect of metals is associated with special types of deformation - martensitic transformations. How does martensitic transformation depend on temperature Also, most shape memory alloys most often contain alloys of copper, aluminum and nickel, as well as nickel and titanium. Widespread use of such materials in various spheres of life. The characteristics of the effect of shape memory and reversible shape memory are considered. The implementation of mechanisms with the memory shape effect is analyzed. The range of applications of these materials is growing day by day and promises many more interesting things. Shape memory materials are the materials of the future.

Shape memory and related phenomena

Effect of W Contents on Martensitic Transformation and Shape Memory Effect in Co-Al-W Alloys