Fe-based Shape Memory Alloys Research Articles

A Measurement of Volume Resistivity in Fe-Based Shape Memory Alloy under Tensile Deformation and its Evaluation of Strain Rate Sensitivity

Fe-based shape memory alloy (Fe-SMA) shows the smaller shape memory effect (SME) compared with the widely-used NiTi alloy. However, because its production cost is much lower than the NiTi alloy, Fe-SMA is challenged to be applied in civil engineering fields such as vibration absorbers and joints. A key of the SME is stress-induced martensitic transformation. Thus, it is important to evaluate an amount of martensite, which can control such excellent performance of Fe-SMA, for increasing a reliability of the Fe-SMA. However, until now, it is quite hard to find studies to evaluate the amount of martensite in Fe-SMA experimentally during deformation at various strain rates, especially during high speed deformation. Instead of the evaluation, it is convenient to capture change in volume resistivity, which has a correlation with the amount of martensite, at various strain rates. In the past, the volume fraction of α’ martensite is evaluated by using a resistance measurement based on the four point-probes method. The advantages of the method are quite simple and relatively high precision, however, its disadvantages are a requirement of strictly-precise reference resistor and power supply, and it is easily affected from noise. In this study, at first, a circuit of Kelvin double bridge with a higher precision is assembled. Then, the rate sensitivity of volume resistivity in Fe-28Mn-6Si-5Cr alloy, which is a kind of Fe-SMA, is experimentally estimated by using the assembled circuit of Kelvin double bridge during tensile testing at various strain rates.

A Study on Tensile Deformation Behavior in Fe-Based Shape Memory Alloy by Rate Sensitive Transformation Kinetics Model

Fe-based shape memory alloy (Fe-SMA) shows a shape memory effect (SME) governed by forward and reverse stress-induced martensitic transformation (SIMT). Fe-SMA has been applied to joints and dampers utilized at various strain rates. To utilize Fe-SMA better, it is necessary to understand the mechanical properties in a wide range of strain rate. In previous study, the results of a tensile test at various strain rates show a rate-sensitivity, however, the mechanism of rate-sensitive tensile deformation behavior is still unclear. Thus, a numerical simulation using a transformation kinetics model is needed to clarify the mechanism. Some transformation kinetics models have been proposed, however, the rate sensitivity cannot be included. In this study, the rate sensitivity of volume fraction martensite is considered into the transformation kinetics model as an improvement of the past-proposed model. The numerical simulation of the uniaxial tensile test at various strain rates is performed to reproduce transformation behavior of the martensite phase. Then, the model is validated by comparing to the experimental results. Afterwards, the mechanism of rate-sensitive tensile deformation behavior of Fe-SMA is discussed.

Measurement of Strain Rate Sensitivity on Transformation Behavior in Fe-based Shape Memory Alloy under Quasi-static Tensile Deformation

Measurement of Strain Rate Sensitivity on Transformation Behavior in Fe-based Shape Memory Alloy under Quasi-static Tensile Deformation

202 体積抵抗率を用いた鉄基形状記憶合金の準静的引張変形下におけるひずみ速度依存性評価(機械材料I)

202 体積抵抗率を用いた鉄基形状記憶合金の準静的引張変形下におけるひずみ速度依存性評価(機械材料I)

Microstructural investigation on marforming and conventional cold deformation in Ni–Ti–Fe-based shape memory alloys

Abstract A hot-rolled Ni–Ti–Fe alloy was subjected to 50% cold rolling by laboratory rolling mill and was subsequently annealed at 800°C for 1.5 h. This sample was then deformed through another 10% reduction in thickness by two different routes (i) conventional cold rolling and (ii) marforming (rolling in liquid nitrogen) followed by annealing under identical conditions. The grain refinement during normal cold rolling was attributed to relatively large presence of dislocations in the ND // <110> grains in the starting microstructure. The regions of higher dislocation densities became gradually textured to ND // <111> orientation, with cold rolling. Marforming (deformation in liquid nitrogen following phase transformation) on the other hand led to more significant grain refinement and also change in the bulk texture. The objective of this study was to compare the grain refinement and microstructural modification produced through marforming with that obtained in conventional cold deformation.

A Comparative Study of Austenitic Structure in NiTi and Fe Based Shape Memory Alloys after Severe Plastic Deformation

The effect of high speed high pressure torsion (HS-HPT) was studied in NiTi and FeMnSiCr SMAs, by comparison. Severe plastic deformation was performed in austenite state for both types of alloys. The alloys subjected to HS-HPT, reduced their grain size due to microstructure fragmentation by compression and torsion. The active elements were achieved being able to support variable ranges of processing parameters like force, pressure, rotation speed and time of torsion. The evolution of microstructural refinement in the samples subjected to different deformation by HS-HPT, were studied by optical and scanning electron microscopy observation and the thermal effect was reveled using differential scanning calorimetry (DSC).

An Experimental Study on Rate-sensitive Tensile Deformation Behaviour of Fe-based Shape Memory Alloy

Recently, it is attempted to apply high manganese steel including Fe-based shape memory alloy to vibration dampers. Especially, the alloy indicates a special characteristic as a well-known shape memory effect. By coupling between this effect and its plastic deformation, it can be considered that its deformation behaviour at higher deformation rate becomes quite complicated and still unclear. In this study, tensile tests of Fe-based shape memory alloy at different rate of deformation are conducted by using two different testing apparatuses such as the conventional material testing machine and impact testing machine based on the split Hopkinson pressure bar technique. In the tests, temperature rise is captured during the quasi-static deformation. After the quasi-static test, the recovery strain due to shape memory effect is measured by heating up the deformed specimens to Af temperature. Finally, the rate sensitivity of the alloy is discussed including the recovery strain.

Factors influencing martensite transitions in Fe-based shape memory alloys

Fe-14Mn-6Si-9Cr-5Ni (mass %) shape memory alloy (SMA) specimens were obtained by powder metallurgy in as-blended state (0_MA) and with particle volume fractions of 10 and 20 % MA’d powders, respectively. After hot rolling and solution treatment, between 973 and 1373 K, the specimens were pre-strained up to 4 %, on a tensile testing machine. The influences of: (i) MA’d fractions, (ii) solution treatment temperature and (iii) pre-straining degree were analysed by X-ray diffraction (XRD), optical (OM) and scanning electron (SEM) microscopy. In this purpose, the gauges of pre-strained specimens were cut and metallographically prepared. Dynamic mechanical analysis (DMA) was employed to emphasize the reverse transformation, during heating, of thermally induced martensite, obtained after solution treatment. The results proved that, as an effect of PM-MA processing, mechanical properties were improved, the amount of stress induced martensite increased and the reverse martensitic transformation was enhanced.

504 A Study on Rate Sensitivity of Tensile Deformation Behavior in Fe-based Shape Memory Alloy by Transformation Kinetics Model

504 A Study on Rate Sensitivity of Tensile Deformation Behavior in Fe-based Shape Memory Alloy by Transformation Kinetics Model

505 Rate Sensitivity in Resistivity of Fe-based Shape Memory Alloy Under Quasi-static Tensile Deformation

505 Rate Sensitivity in Resistivity of Fe-based Shape Memory Alloy Under Quasi-static Tensile Deformation

Cyclic degradation mechanisms in aged FeNiCoAlTa shape memory single crystals

This study focuses on the functional stability of [001]-oriented Fe41Ni28Co17Al11.5Ta2.5 (at.%) single crystals. It is shown that functional degradation of aged FeNiCoAlTa, containing fine dispersed γ′-particles ∼5–8nm in diameter is caused by the interaction of different martensite variants under cyclic loading in tension. Superelastic cycling experiments up to 4.5% total strain resulted in the accumulation of permanent strain mainly caused by the formation of retained martensite. In situ observations were conducted in order to evaluate the local strain evolution and martensite variant interactions on the meso- and microscale. Optical microscopy and transmission electron microscopy observations revealed various differently oriented martensite variants which were retained upon 100 superelastic cycles. In addition, fine martensitic structures remaining in the vicinity of the γ′ precipitates were found after mechanical cycling, which are shown to be important for cyclic degradation in Fe-based shape memory alloys.

An Estimation of Joint Strength by Using Fe-Based Shape Memory Alloy Subjected to Bending Deformation at Various Deformation Rate

In various kinds of shape memory alloy (SMA), Fe-based SMA (Fe-SMA) shows smaller shape memory effect compared with the other SMAs. However, Fe-SMA shows huge advantages on the excellent formability, machinability, etc. Moreover, its production cost is cheaper than other SMAs; therefore, the alloy is attempted to be applied to structural members such as joints and dampers. Since bending deformation at higher deformation rate is generated in the members, especially the joints, due to impact force such as earthquake or wind, a clarification on the bending strength of the joints at various deformation rate is strongly required. In this study, at first, it is attempted that the bending strength and its rate sensitivity of the joints which consist of Fe-based SMA are experimentally estimated by the three-point bending test at various deformation rate. Then, the force balance equation is challenged to be derived to predict the bending strength.

Effect of Deflection Rate on Bending Deformation Behavior of Fe-Based Shape Memory Alloy

In this study, three-point bending test is conducted at various deformation rate by using a thin plate of Fe-based alloy. The rate sensitivity of its bending deformation during loading and shape memory effect by heating after unloading are investigated experimentally. The results obtained are summarized as bellows. (1) In the case where the quasi-static loading was applied, the positive rate sensitivity, which means the stress level increases with increasing the deflection rate, can be observed slightly. (2) It is hard to observe that recovery of deflection by SME depends on deflection rate under quasi-static loading. (3) In the case where the impact loading was applied, the positive rate sensitivity can be observed clearly.

OS0911 Fe-28Mn-6Si-5Cr系形状記憶合金を用いた管継手の曲げ強度の速度依存性

In various kinds of shape memory alloy (SMA), Fe-based SMA (Fe-SMA) shows smaller shape memory effect compared with the other SMAs. However, Fe-SMA shows huge advantages on the excellent formability, machinability, etc. Therefore, it is attempted that the alloy is applied to structural members such as joints and dampers. In this study, at first, the bending strength and its rate sensitivity of the joints made of Fe-SMA are experimentally estimated by the three-point bending test at various deformation rate. Then, it is challenged that the force balance equation is derived to predict the bending strength.

Experimental analysis of Fe-based shape memory alloy behavior under thermomechanical cyclic loading

In this work, the specific thermomechanical behavior of Fe-based Shape Memory Alloys (SMAs) was investigated experimentally. Results show that: (i) such behavior is governed by martensitic transformation and/or plasticity, and depends on both testing temperature and applied mechanical loading level; (ii) phase transformation and plasticity yield stresses are interactive and interdependent; (iii) at low temperatures, the stress-induced martensite is activated first, then followed by plasticity activation at a higher loading level, which leads to a coupling of the two mechanisms; (iv) at high temperatures, plasticity activation precedes the possible formation of strain-induced martensite at high stress levels; (v) behavior under thermomechanical cyclic loading shows that the cumulative plasticity significantly affects the martensitic transformation mechanism. This plasticity seems to prevent martensitic variants from forming, and to reduce the shape memory effect. Finally, the stress–temperature diagram was obtained from these experimental results. It summarizes all the possible Fe-based SMA behavior under various thermomechanical loadings.

A newly developed Fe-based shape memory alloy suitable for smart civil engineering

A nominally new Fe-16Mn-5Si-10Cr-4Ni-1(V, N) (mass %) alloy containing V and N has been developed aiming to precipitate VN particles without training. Transmission electron microscope (TEM) observations have indicated that VN preferentially precipitated on the top of stacking faults and act as nucleation sites for the γ (FCC) →ε phase (hcp) transformation. VN plays a key role in improving the thermo-mechanical properties. The results showed that shape memory properties could be remarkably improved by pre-deformation at room temperature before aging or deformation at low temperature after aging treatment. 44% shape recovery and 440 MP shape recovery stress were achieved when heating to 160 °C after the initial 4% strain at RT. Nearly perfect shape recovery (90%) and shape recovery stress (500 Mpa) have been achieved when the alloy was 4% deformed at −45 °C followed by heating up to 225 °C. Moreover, no relaxation phenomena were found when the tested samples were cooled to room temperature. All of these results suggested the possible practical applications of Fe–Mn–Si SMAs, especially in smart civil engineering.

Effects of amount of pre-deformation on precipitation of NbC particles and shape memory effect of Fe17Mn5Si8Cr5Ni0.5NbC alloy during electropulsing treatment

To further enhance shape memory effect (SME) and improve treatment technique in Fe-based shape memory alloys, an Fe17Mn5Si8Cr5Ni0.5NbC alloy was subjected to electropulsing treatment after pre-deformation. The results show that the shape recovery ratio increases with the amount of pre-deformation up to 10%. The maximum shape recovery ratio after electropulsing treatment is 8% greater than that after ageing at 1073 K. The number of NbC particles induced by electropulsing treatment is increased and the size of the particles is decreased with the amount of tensile pre-deformation up to 10%, and NbC carbides are precipitated more quickly through electropulsing treatment than by ageing.

A constitutive model for Fe-based shape memory alloy considering martensitic transformation and plastic sliding coupling: Application to a finite element structural analysis

In this article, we propose a finite element numerical tool adapted to a Fe-based shape memory alloy structural analysis, based on a developed constitutive model that describes the effect of phase transformation, plastic sliding, and their interactions on the thermomechanical behavior. This model was derived from an assumed expression of the Gibbs free energy taking into account nonlinear interaction quantities related to inter- and intragranular incompatibilities as well as mechanical and chemical quantities. Two scalar internal variables were considered to describe the phase transformation and plastic sliding effects. The hysteretic and specific behavior patterns of Fe-based shape memory alloy during reverse transformation were studied by assuming a dissipation expression. The proposed model effectively describes the complex thermomechanical loading paths. The numerical tool derived from the implicit resolution of the nonlinear partial derivative constitutive equations was implemented into the Abaqus® finite element code via the User MATerial (UMAT) subroutine. After tests to verify the model for homogeneous and heterogeneous thermomechanical loadings, an example of Fe-based shape memory alloy application was studied, which corresponds to a tightening system made up of fishplates for crane rails. The results we obtained were compared to experimental ones.

Macroscopy Lattice Deformation of Martensitic Transformation in Fe-Based Shape Memory Alloy

Macroscopic lattice deformation of martensitic transformation and shape memory effect (SME) were studied by atom force microscopy (AFM), X-ray diffraction and so on. The results showed that stress induced martensitic surface relief was “N”-shaped. The surface relief was parallel distribution when deformation was less than 6%. When relief became to intercross, its height and width were far less than parallel relief in same deformation. Superior heat-recovery was discovered in parallel surface relief. The recovery ratio was very low in intercrossed relief. The macroscopic lattice deformation descends in virtue of relief intercrossed, then recovery process was forbidden, so that recovery ratio was descent.

Methods of Improving Shape Memory Effect of FeMnSiCr Alloy Pipe Joint

The influence of different broaching rate, the training of thermo-mechanical cycle and Electro-pulse Modification (EPM) on the shape memory effect of the FeMnSiCr alloy was investigated. The recovery pulling force can be realized as high as 22850N after EPM treatment. The Fe-based shape memory alloy (SMA) pipe joint can meet the requirement of engineering application.