Fe Mn Si Cr Ni Shape Memory Alloy Research Articles

Unveiling the microstructure evolution and mechanical properties in a gas tungsten arc-welded Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si–Cr–Ni shape memory alloys (SMAs) are unique low-cost materials with shape memory properties that grant them the ability to be used in both functional and structural applications. Such SMAs are especially sought in the construction sector for the creation of new components and/or the reinforcement of damaged ones. In this study, a Fe–17Mn–5Si–10Cr–4Ni–1(V, C) wt% SMA was gas tungsten arc welded, with the objective to investigate the microstructure and mechanical performance changes occurring after welding. A comprehensive assessment of processing, microstructure and properties relationships was established combining microscopy (optical and electron), synchrotron X-ray diffraction, microhardness mapping and tensile testing including cycling assessment of the joint’s functional performance. It is shown that the present SMA has good weldability, with the joints reaching nearly 883 MPa at fracture strain of 23.6 ± 2.1%. Alongside this, several microstructure differences were encountered between the as-received and as-welded condition, including the formation of ferrite and Fe5Ni3Si2 P213 cubic precipitates amidst the fusion zone in the latter region.Graphical abstract

Preparation and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

Preparation and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

Numerical simulation of extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube based on finite element method and cellular automaton

FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is firstly put forward and it can be fabricated by means of isothermal extrusion. Based on Arrhenius constitutive model of FeMnSiCrNi and NiTiNb shape memory alloys, isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube is simulated by rigid viscoplastic finite element method. It can be found that the deformation zone of the dissimilar shape memory alloy composite tube is always in a three-dimensional compressive stress state during extrusion, and the deformation of the inner tube is obviously higher than that of the outer tube. It is necessary to guarantee the interface compatibility between the inner tube and the outer tube during isothermal extrusion of FeMnSiCrNi/NiTiNb dissimilar shape memory alloy composite tube. The relationship between macroscopic process variables and microscopic variables during plastic deformation of FeMnSiCrNi shape memory alloy tube at high temperature is established by coupling finite element simulation and cellular automaton simulation. The microstructural evolution of FeMnSiCrNi shape memory alloy in different deformation zones during isothermal extrusion of dissimilar shape memory alloy composite tube is simulated. It can be concluded that the grain size of dynamic recrystallization is reduced with the increase of plastic strain in the deformation zone.

Nb-doped FeMnSiCrNi coatings: microstructure, phase transformation, shape recovery rate, wear and corrosion resistance

The lower microhardness (only 250 HV0.2) and corrosion resistance are two primary factors that seriously restrain the wide applications of laser cladding FeMnSiCrNi shape memory alloys (SMA) coatings. Herein, SMA/Nbx (x = 1, 3, 5, 7 wt%) composite coatings were fabricated for improving the microhardness and anti-corrosion. The influence of the different Nb doping amounts on the microstructure, microhardness, friction, corrosion resistance and shape recovery rate was studied. In-depth research on the strengthening mechanism by TEM reveals that the formation of Nb3Si significantly impedes the movement of dislocations, and improves the anti-wear and microhardness of the composite coating. Benefiting from doping of Nb, the obtained coating possesses higher Cr element, thus improving the robustness of the passivation film. When the Nb doping is 5 wt%, the Rct was twice as high. Simultaneously, the fabricated coating exhibits a better shape memory effect. The recovery rate reached 4.38% at a deformation of 5% when doping with 5 wt%.

Effects of Ti on microstructure and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

The effects of Ti on the microstructure and properties of Fe–20Mn–6Si–8Cr–5Ni shape memory alloy prepared by powder metallurgy were investigated. The results showed that trace Ti elements could improve the alloy's compressive yield strength and fracture strength. With the increase of Ti, a precipitated phase gradually appeared in the alloy, which adversely affected the mechanical properties of the alloy. The addition of Ti increased the lattice microstrain of the alloy, which provided the driving force for the martensitic phase transformation and facilitated the shape memory properties of the alloy. There was a relationship between the Ti content and the corrosion resistance of the alloy, with a small amount of Ti producing dispersion strengthening to improve the corrosion resistance of the alloy, and an excess of Ti causing composition segregation to make the alloy susceptible to corrosion. Ultimately, 0.5 wt% Ti was found to have good overall mechanical properties with a compressive yield strength of 1567 MPa and fracture strength of 2140MPa, its superelastic strain was 2.8% and 3.1% (at 10% and 15% pre-strain), respectively.

STRUCTURAL CHANGES IN A POWDER METALLURGY 66FE-14MN-6SI-9CR-5NI (MASS. %) SHAPE MEMORY ALLOY SUBJECTED TO BENDING CREEP

Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloy (SMA) has been developed as a commercial grade of Fe-Mn-Si based SMAs with excellent formability and corrosion resistance. Producing FeMnSiCrNi SMAs by powder metallurgy enables a better control of chemical composition and grain size. This paper discusses the variation of bending creep deformation, as a function of time, temperature and force, in the case of a powder metallurgy (PM) Fe-14Mn-6Si-9Cr-5Ni SMA with 50 % mechanically alloyed powder volume. Creep test temperatures were selected based on phase transitions determined by dynamic mechanical analysis (DMA), during heating. The results suggested the tendency of martensite plate variants to reorient along a common direction, after creep.

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in Femnsicrni Shape Memory Alloy Based on Stacking Faults

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in Femnsicrni Shape Memory Alloy Based on Stacking Faults

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in Femnsicrni Shape Memory Alloy Based on Stacking Faults

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in Femnsicrni Shape Memory Alloy Based on Stacking Faults

On the Free Recovery Bending Shape Memory Effect in Powder Metallurgy FeMnSiCrNi

This paper presents the results of an original experimental study on the training capacity of a powder metallurgy (PM) FeMnSiCrNi shape memory alloy (SMA). The specimens were sintered under protective atmosphere from blended elemental powders, 50 vol.%. of alloy particles being mechanically alloyed. Lamellar specimens, hot rolled to 1 mm thickness, were bent against cylindrical calibres with five decreasing radii, to induce cold shapes with higher and higher deformation degree, as compared to the straight hot shape. During the training procedure, bent specimens were heated with a hot air gun, and developed free-recovery shape memory effect (SME) and partially deflected, by reducing their curvature. The first set of experiments involved fastening the specimens at one end, heating it and monitoring free end’s displacement by means of cinematographic analysis. Within the second set of experiments, both cold and hot shapes were recorded and digitalized and their chord’s length (b) and circle segment height (a) were measured and the radius was determined as R = a/2 + b2/8a for the cold (Rc) and hot shapes (Rh). Finally, the shape recovery degree was calculated for the nth calibre as Δrecn = (Rhn-Rrn)/(Rhn-1-Rrn) and the variation of Δrecn with calibre’s radius was discussed.

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in FeMnSiCrNi Shape Memory Alloy Based on Stacking Faults

Formation Mechanism of Austenite Twin and its Suppression of Martensite Transformation in FeMnSiCrNi Shape Memory Alloy Based on Stacking Faults

Powder Metallurgy: An Alternative for FeMnSiCrNi Shape Memory Alloys Processing

In the case of quintenary Fe-Mn-Si-Cr-Ni shape memory alloys (SMAs), ingot metallurgy (IM) has technological shortcomings concerning compositional segregation, imperfect melt-incorporation of Si, demanganization during heating and cooling-induced cracking, which can be effectively surmounted by combining powder metallurgy (PM) with mechanical alloying (MA). The paper reviews the results reported in the processing and characterization of PM-MA’ed FeMnSiCrNi SMAs, with special emphasis on the findings obtained by present authors in the last decade. Specimens with nominal chemical compositions Fe-18Mn-3Si-7Cr-4Ni and Fe-14Mn-6Si-9Cr-5Ni (mass %) were produced by IM and PM. In the latter case various volume fractions of as-blended powders were MA’ed under protective atmosphere, before being pressed and sintered. Further compacting, up to 5 % porosity degrees, was achieved by hot rolling. Structural analysis, performed by X-ray diffraction and scanning electron microscopy, revealed the formation of unusually large amounts of α’-body centred cubic (bcc) thermally induced martensite. This undesirable martensite seemed to be destabilized by tensile pre-straining, and enabled PM specimens to reach higher stresses than IM ones. The formation and accumulation of α’-bcc stress induced martensite was enhanced by tensile pre-straining, mechanical cycling and augmentation of MA’ed powder fraction. It has been argued that the optimization of technological processing parameters of heat treatment (HT) and hot rolling (HR) combined with MA’ed powder fraction caused the augmentation of shape memory effect (SME) magnitude. DMA-temperature scans revealed an increasing tendency of internal friction (tan δ) with MA’ed powder fraction, as well as the presence of two tan δ maxima ascribed to antiferromagnetic-paramagnetic transition and martensite reversion to austenite, respectively. DMA-strain sweeps emphasized the occurrence of a plateau on the storage modulus vs. strain amplitude variation which was associated with stress-induced formation of ε hexagonal close-packed (hcp)-martensite. In spite of large α’-bcc amounts, PM-MA’ed Fe-14Mn-6Si-9Cr-5Ni experienced free-recovery SME which was enhanced by thermomechanical training. Coupling rings, meant to connect vibrating pipes that transport turbulent fluids, being able to mitigate vibrations that could accidentally open the connection, were manufactured and tested.

Role of stacking faults in martensite transformation of FeMnSiCrNi shape memory alloy subjected to plastic deformation at high temperatures

FeMnSiCrNi shape memory alloy (SMA) undergoes plastic deformation at high temperatures, including 850, 900, 950 and 1000 °C. All the deformed FeMnSiCrNi samples consist of γ austenite and ε martensite, where the orientation relationship between γ austenite and ε martensite is [110]γ//[21¯1¯0]ε. Furthermore, ε martensite increases with increasing deformation temperature. Stacking faults play a predominant role in martensite transformation of FeMnSiCrNi SMA. The mechanisms of martensite transformation are revealed based on slip of Shockley partial dislocation as well as formation of intrinsic and extrinsic stacking faults. The critical transformation stress of FeMnSiCrNi SMA is further put forward based on stacking fault energy. Quenching stress plays an important role in martensitic transformation of FeMnSiCrNi SMA.

Stress-induced martensite phase transformation of FeMnSiCrNi shape memory alloy subjected to mechanical vibrating polishing

Abstract Fe66Mn15Si5Cr9Ni5 (wt.%) shape memory alloy (SMA) with γ austenite and e martensite was subjected to mechanical vibrating polishing and consequently its surface suffered from plastic deformation in the case of compressive stress. Almost complete e martensite transformation is found to occur in FeMnSiCrNi sample subjected to mechanical vibrating polishing, where stress-induced martensite transformation plays a predominant role. Stress- induced martensite transformation of FeMnSiCrNi SMA is closely related to the orientation of external stress. The complicated compressive stress which results from the mechanical vibrating polishing contributes to e martensite transformation from γ austenite of FeMnSiCrNi SMA. Mechanical vibrating polishing has a certain influence on the surface texture of e martensite of FeMnSiCrNi SMA, where texture appears in the polished FeMnSiCrNi SMA.

On the significance of C and Co on shape memory performance of Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si bearing shape memory alloys are used as structural and functional materials, and have the potential for application in industrial and architectural fields. Fe–Mn–Si–Cr–Ni based shape memory alloys were selected to elucidate the impact of C and Si content on shape memory effect, where Si was replaced by Co. In this regard, Fe–15Mn–5Si–8Cr–5Ni, Fe–15Mn–5Si–8Cr–5Ni-0.1C, and Fe–15Mn–3Si–8Cr–5Ni-0.1C–2Co alloys were designed to simultaneously elucidate the shape memory effect (SME) and mechanical properties in relation to the microstructure. The study indicated that the addition of 0.1 wt% C significantly improved the SME of Fe–Mn–Si–Cr–Ni alloy, and the shape recovery rate of Fe–15Mn–5Si–8Cr–5Ni-0.1C alloy aged at 750 °C for 4 h was maximum at 55.45%. The content of thermally-induced martensite was reduced, which led to decrease in the probability of α′-martensite formation, and promoted inverse transformation of stress-induced martensite and enhanced the shape memory effect. In addition, the strength of the parent phase was enhanced by segregation of elements during aging. Furthermore, the plastic deformation involving slip during stress-induced martensitic transformation was reduced. The reduced content of α′-martensite promoted reversal of stress-induced martensite. On the other hand, Co increased the stacking fault energy and reduced nucleation of stress-induced martensite, such that the number density of stacking faults decreased the shape memory effect of the experimental steel.

Hot workability of FeMnSiCrNi shape memory alloy based on processing map and martensitic transformation

Hot workability of Fe66Mn15Si5Cr9Ni5 (wt.%) shape memory alloy (SMA) with γ austenite and ε martensite at room temperature was investigated by establishing processing map and simultaneously considering martensitic transformation. All the FeMnSiCrNi samples subjected to hot deformation are composed of ε martensite and γ austenite. Furthermore, the higher temperature results in the larger fraction of ε martensite, whereas the higher strain rate leads to the smaller fraction of ε martensite. Simultaneously, the higher temperature or the lower strain rate leads to the larger grain size. In addition, dislocations, stacking faults and austenite twins appear in the deformed samples. According to processing map, the optimal hot processing parameters for the FeMnSiCrNi SMA is determined as the temperature range of 850–925 °C at the strain rate below 0.0008 s−1 and the temperature range of 925–1000 °C at the strain rate range of 0.001–0.03 s−1. Furthermore, the existence of ε martensite in the deformed FeMnSiCrNi samples has an adverse effect on shape memory effect of FeMnSiCrNi SMA. In addition, dynamic recrystallization (DRX) and subsequent martensitic transformation weaken the textures of the grains with γ austenite phase in the deformed FeMnSiCrNi SMA samples. Therefore, it is necessary to prevent FeMnSiCrNi SMA from being subjected to hot workability in the case of too high temperatures or too low strain rates.

Constitutive behavior and microstructural evolution of FeMnSiCrNi shape memory alloy subjected to compressive deformation at high temperatures

Constitutive behavior and microstructural evolution of FeMnSiCrNi shape memory alloy (SMA) subjected to compressive deformation at high temperatures were investigated based on the different deformation conditions. According to Arrhenius type equation, the constitutive equation of FeMnSiCrNi SMA was constructed according to strain compensation, where material parameters vary with increasing strain. The involved constitutive equation can effectively predict the flow stress during dynamic recrystallization (DRX) of FeMnSiCrNi SMA. All the compressed FeMnSiCrNi samples consist of ε martensite and γ austenite. In addition, dislocations, stacking faults and austenite twins were also found in the deformed FeMnSiCrNi samples. Owing to the occurrence of DRX, the grain size increases with increasing deformation temperature. Furthermore, with increasing deformation temperature, the fraction of large angle grain boundaries increases while the one of low angle grain boundaries decreases. Deformation temperature also affects the texture of FeMnSiCrNi SMA. With increasing deformation temperature, 〈110〉 texture becomes weak gradually in the γ austenite, but 〈001〉 texture and cube texture are intensified gradually along with the onset of 〈110〉 and 〈111〉 fiber textures. Moreover, ε martensite possesses 112¯2 fiber texture.

Investigation of the Dynamic Recrystallization of FeMnSiCrNi Shape Memory Alloy under Hot Compression Based on Cellular Automaton

Dynamic recrystallization (DRX) takes place when FeMnSiCrNi shape memory alloy (SMA) is subjected to compression deformation at high temperatures. Cellular automaton (CA) simulation was used for revealing the DRX mechanism of FeMnSiCrNi SMA by predicting microstructures, grain size, flow stress, and dislocation density. The DRX of FeMnSiCrNi SMA has a characteristic of repeated nucleation and finite growth. The size of recrystallized grains increases with increasing deformation temperatures, but it decreases with increasing strain rates. The increase of deformation temperature leads to the decrease of the flow stress, whereas the increase in strain rate results in the increase of the flow stress. The dislocation density exhibits the same situation as the flow stress. The simulated results were supported by the experimental ones very well. Dislocation density is a crucial factor during DRX of FeMnSiCrNi SMA. It affects not only the nucleation but also the growth of the recrystallized grains. Occurrence of DRX depends on a critical dislocation density. The difference between the dislocation densities of the recrystallized and original grains becomes the driving force for the growth of the recrystallized grains, which lays a solid foundation for the recrystallized grains growing repeatedly.

Thermo-mechanical effects caused by martensite formation in powder metallurgy FeMnSiCrNi shape memory alloys

ABSTRACTThe paper reports solution treatment (ST) and mechanical alloying (MA) effects on the structure and static/dynamic mechanical behaviour of PM-MA’ed FeMnSiCrNi shape memory alloys associated with the formation of thermally and stress-induced martensite. The specimens were subjected to tensile pre-straining, in order to stress induce martensite and their gauges were cut and prepared for X-ray diffraction (XRD) as well as for optical and scanning electron microscopy (SEM). XRD patterns allowed determining the presence of large amounts of α′-body centred cubic (bcc) besides ε-hexagonal close packed (hcp) martensite and γ-face centred cubic (fcc) austenite. The decrease in the amount of α′-bcc at specimens ST’ed at 1273 and 1373 K, with increasing pre-straining degree, was confirmed by XRD patterns and SEM micrographs. Dynamic mechanical analysis (DMA) was performed by strain sweeps (SS). The SS-DMA graphs displayed storage modulus plateaux which were associated with the formation of ε-hcp martensite.

Anomalous cyclic oxidation behaviour of a Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si–Cr–Ni alloys are known by their shape memory properties, however, oxidation studies are still incipient. This study evaluated an Fe-17Mn-5Si-10Cr-4Ni-VC alloy on cyclic oxidation tests at 800, 900 and 1000°C. Mass variation was evaluated and oxide layers were examined by SEM, EDS and XRD. An anomalous mass variation was observed: after initial spallation, the material restarted mass gain. The formed Mn-depleted zone changed the austenite microstructure to ferrite on the metal/oxide interface and better oxide anchoring was promoted through the roughness generated. The result makes this alloy an interesting candidate for applications where cyclic oxidation is an important issue.

Effect of titanium addition on shape memory effect and recovery stress of training-free cast Fe–Mn–Si–Cr–Ni shape memory alloys

The shape memory effect and recovery stress of cast Fe–17.2Mn–5.28Si–9.8Cr–4.57Ni (18Mn) and Fe–17.5Mn–5.29Si–9.68Cr–4.2Ni–0.09Ti (18Mn–Ti) alloys have been investigated by optical microscopy, scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and resistivity–temperature curves. The cast 18Mn and 18Mn–Ti alloys solidified as the ferritic mode for which liquid phase fully transforms into primary δ ferrite. The role of titanium is to indirectly refine the austenite through refining the primary δ ferrite. In this case, the austenitic grains of the cast 18Mn alloy were much bigger than that of the cast 18Mn–Ti alloy, although the two alloys underwent δ→γ phase transformation. Grain refinement suppresses the stress-induced ε martensitic transformation, and thus the shape memory effect of the cast 18Mn–Ti alloy is worse than that of the cast 18Mn alloy. On the contrary, the maximum recovery stress and the recovery stress at room temperature are higher for the cast 18Mn–Ti alloy annealed at 1073K for 30min than for the cast 18Mn alloy annealed at 973K for 30min, because grain refinement suppresses the relaxation of recovery stress caused by the plastic deformation and the stress-induced ε martensitic transformation during cooling process. It is difficult to obtain the training-free cast Fe–Mn–Si based shape memory alloys with excellent shape memory effect and high recovery stress only by grain refinement.