Fe-based Shape Memory Alloys Research Articles

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.

Development of Texture and Microstructure During Cold Rolling and Annealing of a Fe-Based Shape Memory Alloy

Texture evolution and microstructural changes during cold rolling and annealing of Fe-14Mn-6Si-9Cr-5Ni shape memory alloy have been investigated. The starting solution-annealed material has a nearly random texture with microstructure composed of equiaxed austenite grains with e martensite plates inside. Cold rolling induces a strong alloy type texture with Brass {011}〈211〉 and Goss {011}〈100〉 as major components. Annealing of the cold-deformed material produces a nearly random texture. The microstructural investigation reveals that with increase in cold deformation, the amount of stress-induced e and α′ martensite volumes increase. The electron back-scattered diffraction (EBSD) phase mapping shows that reversion of the e martensite begins only after recrystallization sets in at a temperature of 1073 K.

S0303-1-6 鉄系形状記憶合金の力学特性に関する実験的研究(形状記憶合金の特性と応用展開(1))

The purpose of this research is to clarify basic mechanical properties and shape memory properties of Fe based shape memory alloy (SMA). In this study, we performed the tensile tests under room temperature to Fe based SMA and observed the shape recovery behavior. In this paper, the obtained results are shown and discussed.

Modelling of martensitic transformation and plastic slip effects on the thermo-mechanical behaviour of Fe-based shape memory alloys

In this paper, we propose a thermo-mechanical three-dimensional constitutive law adapted to Fe-based shape memory alloys. It takes into account the effect of the martensitic transformation and the plastic slip mechanisms and their interaction. The adopted formulation is based on a simplified micromechanical description. The macroscopic behaviour is derived by considering the equivalent homogeneous effect on a representative volume element. The Gibbs free energy expression is defined. Thermodynamic driving forces are then derived and compared to critical forces leading to the constitutive equations solved by Newton–Raphson numerical scheme. Obtained results for thermo-mechanical loadings are compared to experimental ones.

Further improvement of shape memory effect in a pre-deformed Fe–Mn–Si–Cr–Ni–Nb–C alloy by smaller NbC precipitated through electropulsing treatment

To further enhance shape memory effect (SME) and improve treatment technique in Fe-based shape memory alloys, a pre-deformed Fe17Mn5Si8Cr5Ni0.5NbC alloy was subjected to electropulsing treatment. The results showed that the maximum shape recovery ratio after electropulsing treatment was 12% greater than that after ageing at 1073 K. SEM observation showed that NbC carbides induced by electropulsing treatment were precipitated more quickly and the amount of NbC particles was increased and the size of NbC particles was smaller.

Identification of ɛ martensite in a Fe-based shape memory alloy by means of EBSD

Ferrous shape memory alloys (SMAs) are often thought to become a new, important group of SMAs. The shape memory effect in these alloys is based on the reversible, stress-induced martensitic transformation of austenite to ɛ martensite. The identification and quantification of ɛ martensite is crucial when evaluating the shape memory behaviour of this material. Previous work displayed that promising results were obtained when studying the evolution of the amount of ɛ martensite after different processing steps with Electron BackScatter Diffraction (EBSD). The present work will discuss in detail, on the one hand, the challenges and opportunities arising during the identification of ɛ martensite by means of EBSD and, on the other hand, the possible interpretations that might be given to these findings. It will be illustrated that although the specific nature of the austenite to ɛ martensite transformation can still cause some points of discussion, EBSD has a high potential for identifying ɛ martensite.

Prediction of martensite and austenite start temperatures of the Fe-based shape memory alloys by artificial neural networks

In this study, martensite start (Ms) and austenite start (As) temperatures of Fe-based shape memory alloys (SMAs) were predicted by using a back-propagation artificial neural network (ANN) that uses gradient descent learning algorithm. An ANN model is built, trained and tested using the test data of 85 Fe-based SMAs available in literature. The input parameters of the ANN model are weight percentages of seven elements (Fe, Mn, Si, Ni, Cr, Cu and Al) and three different treatment conditions (hot rolling, homogenizing temperature and quenching). The ANN model was found to predict the Ms and As temperature well in the range of input parameters considered. A computer program was devised in MATLAB and different ANN models were constructed with this program for prediction of As and Ms temperatures of iron-based SMAs. A comprehensive analysis of the prediction errors of Ms and As temperatures made by the ANN is presented. This study demonstrate that ANN is very efficient for predicting the Ms and As temperatures of iron-based SMAs.

Effect of Carbon on the Shape Memory Mechanism in FeMnSiCrNi SMAs

Fe-Mn-Si-Cr-Ni alloys are Fe-based shape memory alloys (SMA), which make use of the γ↔e stress induced martensitic transformation. In the present study, the effect of C addition on the shape memory effect was reported. The characterization of the martensitic transformation and the phase components was carried out by using light optical microscopy, X-ray diffraction, internal friction measurements and transmission electron microscopy (TEM). C is often mentioned to improve the shape memory behaviour. Present results show, however, an opposite effect. It is believed that the relative position between the deformation temperature and the M s temperature for the two alloys is of key importance when looking for an explanation for the presented experimental results. The lower M s temperature for the high C alloy causes more slip and less transformation of the austenite. The microstructural characterization showed a lower amount of formed e martensite during deformation for the high C alloy.

Magnetic-Field-Induced Strain of Fe-based Ferromagnetic Shape-Memory Alloy in a Pulsed Magnetic Field

AbstractThe magnetic field-induced strain (MFIS) of the martensite metallic compound Fe3Pt were studied in a pulsed magnetic field using the capacitance method at low temperatures down to 4.2 K in a martensitic phase, which is much lower than the martensitic transformation temperature TM = 85 K. After zero field cooling, pulse magnetic field with the maximum frequency of 160 Hz was applied parallel to [001]p axis. Large MFIS has been measured. The value of the MFIS is ΔL/L = −1.7 %. When the magnetic field was decreased, the recovery of the strain was observed. At the 2nd shot, the strain of about 0.6 % was observed. It means that MFIS occurs even in short-pulse magnetic fields.

Suggestion of Pipe Coupling Method for Maximum and Uniform Joining Stress

A new method of pipe joining using shape memory alloys (SMAs) is proposed in this study to obtain the maximum and uniform joining stress. Fe-based SMAs, regarded as potential alloys for pipe couplings, is not so widely industrialized as anticipated. The major obstacle is error of pipe size, which causes a gap between deformed SMA joint and pipes to be joined prior to heating. Since the recoverable strain of Fe SMAs is comparable to the gap, most of the strain is wasted as free recovery. In this study, the problem is settled by deforming simultaneously SMA coupling and pipes to be joined with the coupling inserted in the pipes. By doing so, there is always no gap between coupling and pipes prior to heating. The new method makes it possible to apply alloys with a poor shape memory effect (SME) to pipe couplings. Some other expected advantages and disadvantages will be discussed.

Shape Memory Effect and Crystallographic Investigation in VN Containing Fe-Mn-Si-Cr Alloys

An industrial application of Fe-based shape memory alloys for joining the pipes in tunnel making constructions requires the proof stress over 400 MPa and 3.5% shape recovery strain. To meet such standards in civil engineering, the Fe-base shape memory alloy containing highdensity of coherent VN precipitates has been developed by designing the composition of the Fe-28Mn-6Si-5Cr (mass%) alloy containing 1.5 vol% VN compounds. In order to make clear the mechanism of enhancement of the proof stress and shape recovery strain, crystallographic investigations were carried out using optical microscopy, X-ray diffraction and high-resolution electron microscopy. The {111}-composed octahedral shaped VN precipitates are formed coherently with a cube-to-cube orientation relationship with the matrix, i.e., ð001ÞP kð 001ÞM and ½100� P k½ 100� M. The precipitates are surrounded by the misfit dislocations at every 8 layers of the (100) planes, which is in agreement with the estimation of the lattice mismatch between the precipitate and the matrix phase. The enhancement of shape recovery is explained by the reversible movement of transformation dislocations left around the precipitates in connection to the residual stress yielded by martensite transformation around the precipitates. It is also suggested that the recovery strain could be proportional to the total number of precipitates.

Martensitic transformation in Fe-based shape memory alloys under magnetic field

Effects of magnetic field on martensitic transformations have been examined in order to know a magnetic field-induced martensitic transformation by using Fe 3 Pt and Fe-Ni-Co-Ti shape memory alloys and an Fe-Ni alloy polycrystals, and control of variants by magnetic field by using Fe-Pd, Ni 2 MnGa and Fe 3 Pt shape memory alloy single crystals. Following results were obtained: (i) The effects of magnetic field on the martensitic transformation start temperature is explained by the equation proposed by our group. (ii) Magnetoelastic martensitic transformation (maretensites are induced only while a magnetic field is applied and are transformed back to the parent phase when the magnetic field is removed ) appears in an ausaged Fe-Ni-Co-Ti shape memory alloy. (iii) In Fe-31.2Pd(at.%), whose easy axis is the a-axis in martensite state, a large expansion of about 3% appears in [001] P (P is the symbol of the parent phase) direction at 77 K by applying a magnetic field along [001] P direction. In Ni 2 MnGa, whose easy axis is the c-axis in martensite state, a large contraction of about 3.8% appears in [001] P direction at 77K by applying a magnetic field along [001] P direction. These strains are nearly the same as those expected from perfect conversion to the preferred variants under magnetic field. In Fe 3 Pt, whose easy axis is the c-axis in martensite state, a large contraction of about 2.3% appears in [001] P direction at 4.2 K by applying a magnetic field along [001] P direction, and a part of this contraction (0.6%) recovers as the field is removed. Considering results of (iii), the mechanism of conversion of variants by magnetic field is discussed.

Finite Element Analysis of Transformation Behavior of an Fe-Based Shape Memory Alloy

Finite Element Analysis of Transformation Behavior of an Fe-Based Shape Memory Alloy

Simulation of martensitic transformations in TRIP-steel and Fe-based shape memory alloy

Several important effects in the mechanical behavior of materials are due to martensitic transformations. In case of TRIP-steels, the γ→ α ′ martensitic transformation during plastic deformation is responsible for high strength combined with an outstanding ductility. Another martensitic transformation ( γ→ ε) is the reason for the perfect shape recovery in Fe-based shape memory alloys (SMAs). By means of a finite element analysis the evolution of martensite both in a TRIP-steel and in an Fe-based SMA is investigated. The model is able to explain the experimentally observed dependence of the austenite start temperature in an Fe-based SMA on the extent of prior martensitic transformation. Dilatometric experiments with an high-alloyed TRIP-steel are used to validate the predictions of the TRIP-simulations.

Corrosion Behaviors of Fe-Based Shape-Memory Alloys

Corrosion Behaviors of Fe-Based Shape-Memory Alloys

The corrosion behavior of Fe-based shape memory alloys

Fe–30Mn–6Si, Fe–30Mn–6Si–5Cr and Fe–13Mn–5Si–12Cr–5Ni shape memory alloys were prepared by a VIM technique. The various corrosion tests were conducted to investigate the corrosion behaviors of these alloys. Experimental results show that in 3.5% NaCl solution, the Fe–13Mn–5Si–12Cr–5Ni alloy had the best chemical corrosion resistance, whereas the Fe–30Mn–6Si–5Cr alloy was locally attacked, forming many corrosion pits after immersion test. In addition, the detachment of the corrosion product covering the Fe–30Mn–6Si alloy caused an abrupt increase in the weight loss. After 2 h of heat treatment at 1000 °C, the corrosion potential of the Fe–30Mn–6Si alloy increased due to the formation of α-ferrite, while the Fe–30Mn–6Si–5Cr alloy became more active. In the stress-corrosion cracking test, the Fe–13Mn–5Si–12Cr–5Ni alloy, having the highest fracture stress in the atmosphere among these alloys, exhibited the largest decrease in fracture stress in the saturated H 2S solution due to the existence of α-martensite.

Microstructures in an Fe Based Shape Memory Alloy and Al Based Dual Phase Crystals after High Speed Deformation

Microstructures have been examined after high-speed deformation given by free weight drop and air gun shooting. Special care was exercised to control the amount of plastic strain so that the deformed specimen could be examined as a function of total plastic strain as well as strain rate. Al based dual phase alloys of Al-Al 3 Fe, Al-Al 3 Ti and Al-Al 3 Ni have been examined both at slow and high-speed strain rates using sheet specimens of various thickness, in order to find strain rate effects on the deformability of the ordered second phase particles embedded in Al. The ordered phases, not deformable at a low strain rate in the Al based alloys, are shown to be deformed by dislocation glide in the high strain rate tests. The another aspect of the study is concerned with the mechanical and structural changes in Fe-Mn-Si based shape memory alloys by high-speed deformation. The shape recovery under the opposing stress is found to increase notably after the shape deformation given by shock loading. Also, the effect of shock loading was examined using a thin foil specimen prepared for electron microscopy. In these tests, thin foil regions were locally amorphized presumably by the heavy shear deformation induced at high strain rate.

A slant type shape memory alloy

A heat-treated Fe-based shape memory alloy (SMA) has compatible properties, magnetization and shape memory effect (SME). Since SME depends on the heat treatment conditions (temperature and time), we produced a slant-type SMA that has a gradient SME value in the longitudinal direction of the specimen. It is obvious that sheet specimen is superior to wire because the value of SME as a slant SME shows greater efficiency than that of wire.

Occurrence of ferromagnetic shape memory alloys (invited)

This article presents an overview of the necessary conditions for the formation of shape memory alloys (SMAs) and how these must overlap with the occurrence of ferromagnetism so that ferromagnetic shape memory alloys (MSMAs) may be formed. The electronic, elastic, and geometric conditions permit an understanding of the occurrence of Cu- and Fe-based SMAs as well as NiMnGa Heusler MSMAs except that the naively determined critical electron concentration for the latter, 7.3, disagrees with the values of 1.5 and 8.6 accepted for the Hume–Rothery phases and certain Fe-based systems.