Fe Mn Si Research Articles

Microstructure, Damping Effect, Shape Recovery, and Nanoprecipitation of Hot and Cold Rolled Fe–30Mn–6Si–6Cr Shape Memory Alloy

Microstructure, Damping Effect, Shape Recovery, and Nanoprecipitation of Hot and Cold Rolled Fe–30Mn–6Si–6Cr Shape Memory Alloy

Microstructure and Mechanical Properties of Gas Metal Arc-welded Fe–Mn–Si Seismic Damping Alloy

Microstructure and Mechanical Properties of Gas Metal Arc-welded Fe–Mn–Si Seismic Damping Alloy

Laser Powder Bed Fusion of Fe–Mn–Si based shape memory alloys with high performance at room and cryogenic temperature

A Fe–Mn–Si based alloy with high shape memory effect (SME) and mechanical performance at both cryogenic and room temperature was fabricated by laser powder bed fusion (LPBF) with blended elemental powders. The effect of laser power on the elemental uniformity, microstructure, SME, strength of the as-built sample was investigated. The developed alloy shown superior SME under high laser power, due to the fully transformation of initial bcc phase to the stable fcc phase during the cooling process. The developed Fe–Mn–Si alloy shown high shape recovery rate of 63 % and 92 % after ∼0.05 bending strain at room and cryogenic temperature, respectively. The as-built samples had characteristic microstructure of small fcc phase grains and high density of stacking faut and twins. The as-built sample exhibited room/cryogenic tensile strength as high as 962MPa/1372 MPa, respectively, with considerable plasticity. This work provides foundations for fast development of high performance additively manufactured shape memory alloy (SMA).

Insights into reduction of hysteresis in (Mn, Fe)2(P, Si) compounds by experimental approach and Landau theory

The giant magnetocaloric effect in (Mn, Fe)2(P, Si) based alloys arises from a magnetoelastic ferromagnetic-paramagnetic (FM-PM) phase transition accompanied by a large thermal hysteresis. The thermal hysteresis leads to an undesirable irreversibility of the magnetocaloric effect (MCE) during cyclic operation, impeding the practical application in solid-state magnetic refrigeration. Here, we present pre-existing PM nuclei play a role in reducing hysteresis. A combinatorial analysis, using in situ X-ray diffraction (XRD) and magneto-optical Kerr effect (MOKE) microscopy, reveals that the residual PM phases at the ferromagnetic state of the compound acts as the nuclei for the growth of the PM phases. This is kinetically favorable for the FM-PM phase transition and contributes to a smaller hysteresis from an extrinsic perspective. In addition, the smaller changes in the lattice constants during the phase transition indicates a weakened first-order phase transition. Through a combined effect of intrinsic and extrinsic contributions, a giant MCE in the magnetic entropy change of 16 J kg–1 K−1 under 2 T and a low thermal hysteresis of 3.0 K were achieved in a basic Mn–Fe–Si–P quaternary system for room temperature applications. Furthermore, based on Landau theory and experimentally obtained data, we established an H-T phase diagram and unveiled the crucial role of the magnetoelastic coupling in manipulating thermal hysteresis. Overall, the findings in this work offer a strategy to mitigate hysteresis while retaining a large MCE through extrinsic control.

Effect of Ferrite Second Phase on Shape Memory Effect of Corrosion‐Resistant Fe–Mn–Si Shape Memory Alloy

At present, Fe–Mn–Si shape memory alloy with high corrosion resistance has become the focus of attention because of its special requirements in some fields. On the basis of Fe–Mn–Si shape memory alloy, a corrosion‐resistant shape memory alloy was designed by adding Cr and other alloy elements. The microstructure characteristics and phase ratio control mechanism of the annealed alloy and the influence mechanism of the second phase (ferrite) and ratio on the alloy memory effect are emphatically studied. The results show that ferrite and austenite are evenly distributed at low annealing temperature, and there is thermal‐induced ε‐martensite at the same time. Appropriate thermal‐induced ε‐martensite can strengthen the austenite matrix, and the shape recovery rate is high at this time. With the increase of annealing temperature, the volume fraction and grain size of ferrite increase, the volume fraction of thermal‐induced ε‐martensite and austenite decreases, and the shape recovery rate decreases, but it is beneficial to improve the corrosion resistance.

Shear strengthening of damaged reinforced concrete beams with iron-based shape memory alloy (Fe-SMA) strips: numerical and parametric analysis

Shape memory alloys (SMAs) are metallic materials that are characterized by their ability to restore their original shape after large deformation when activated by heating. This unique property renders SMAs appealing for various civil engineering applications. Iron-based SMAs (Fe-SMAs), including alloys like Fe–Mn–Si, stand out due to their cost-effectiveness and high strength. The primary focus of this research lies in the computational modeling of Fe-SMA strips utilized to reinforce damaged concrete structures. To achieve this, details from an experimental test are leveraged for the computational simulation of real-scale reinforced concrete beams that were first loaded to some level of damage, then released and strengthened, and subsequently retested. The strengthening approach involves the application of external Fe-SMA strips wrapping around the beams. This paper presents an original computational modeling setup that incorporates a switch option for the Fe-SMA material. This feature enables one to use a single simulation platform for the whole process. The significance of this method originates from its capacity to ensure a robust analysis that includes all simulation steps-testing unstrengthened beams, installing and heating Fe-SMA strips, and testing both damaged and strengthened beams—in a single, multi-step analysis. The computational simulation results were compared with the outcomes of the experimental test, revealing an acceptable level of agreement. The findings indicate a substantial increase in both shear strength and ductility as a result of the application of Fe-SMA strips. Additionally, parametric and mesh sensitivity studies were conducted. These aimed to investigate the mesh dependency of the model and to identify the optimal mesh size. Furthermore, variations in the details of the Fe-SMA strips, including thickness, width, quantity, and effect of applied temperature were explored to compare the outcomes of different applications of these strips.

The shape recovery behavior of compressively deformed Fe–Mn–Si–Cr–Ni alloys

Cylindrical alloys fabricated from shape memory Fe–xMn–5Si–5Ni–yCr were produced by utilizing diverse solid volume fractions through the use of the powder metallurgy and sintering technique. The shape recovery due to compressive force was analyzed and correlated with the volume fractions. A higher concentration of manganese (Mn) will result in a decrease in shape recovery as a result of the formation of oxides, precipitates and unintended intermetallics during the furnace cooling process. The dislocation occurring within and around the grain boundary is another significant factor contributing to the reduction in shape recovery. The increase in chromium (Cr) content reduces the likelihood of dislocation around the grain boundary. The effectiveness of compressive deformation was examined and correlated.

Microstructural mechanism underlying the stress recovery behavior of a Fe–Mn–Si shape memory alloy

Recovery stress governs the prestress strengthening effect of Fe–Mn–Si-based shape memory alloys in civil engineering applications. Although the effects of grain size, texture, and precipitates on recovery stresses have been extensively studied, the generation of recovery stress has not been thoroughly discussed regarding martensite growth behavior, especially considering the interaction of martensite variants. This study investigates the stress recovery and ε martensite growth behavior of a Fe–30Mn–6Si–5Cr (wt.%) alloy subjected to varying levels of deformation. The Fe–30Mn–6Si–5Cr (wt.%) alloy exhibits a yield strength of approximately 450 MPa, with an ultimate elongation of 44 % and a tensile strength of 950 MPa observed in uniaxial incremental cyclic tensile tests. Additionally, the results reveal an initial increase in recovery stress with pre-strain, peaking at 7 %, followed by a subsequent decrease with further deformation. With increasing pre-strain, the primary ε martensites initially grow parallelly, followed by the appearance of secondary martensites with a different orientation, intersecting multiple parallel primary martensites along with the increasing density of dislocations and stacking faults. A microstructural mechanism is proposed to elucidate the stress recovery behavior, encompassing the impact of primary martensites and secondary martensites interaction, and the influence of dislocations and stacking faults. This work offers microstructural scenarios that help to understand the generation of recovery stress and provides guidance for regulating recovery stress in Fe–Mn–Si-based shape memory alloys for civil engineering applications requiring prestress strengthening.

Reverse ε→γ transformations of temperature-induced and stress-induced martensites in Fe–Mn–Si alloys with shape memory effect

In this work we argue that the reverse martensitic transformation (MT) of the stress-induced martensite (SIM) of Fe–Mn–Si-based alloys for moderate prestrains occurs in essentially thermoelastic-like way, in contrast to non-thermoelastic MT of temperature-induced martensite (TIM). We compare, using a number of complementary experimental techniques, the temperatures and the kinetics of the reverse ε→γ martensitic transformation of SIM and TIM for commercial and model Fe–Mn–Si alloys after various thermomechanical treatments. We claim that two studied phenomena are generic in Fe–Mn–Si-based alloys of different compositions and microstructure: first, opposite to the conventional effect of stabilization of martensite by prestrain, the reverse MT during heating of alloys prestrained in bending and tension starts well below (up to 100 K) the start temperature of the reverse MT for the TIM of the same alloy. The difference between engineering temperatures of the start of the reverse transformation, As, for SIM and TIM reaches ca. 50 K, pointing to a need to consider different As for TIM and SIM, AsTIM and AsSIM. Second, the reverse transformations of TIM and SIM show very different kinetics. The reverse MT of SIM is diffuse over the temperature range exceeding 100 K. The reverse MT of TIM, on the contrary, is well localized within the temperature range of ca. 20 K. The experimental observations can be interpreted assuming that, due to the differences in the formation mechanisms of SIM and TIM, the latter shows non-thermoelastic behaviour, whereas the SIM shows similarities with the thermoelastic martensites stabilized by prestrain.

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

Effect of local loading on microstructure and enhanced mechanical property of large complex castings prepared by Al–Si–Fe–Mn–Mg–Cu alloy during squeeze casting

Flywheel shells with a complex structure and large wall-thickness difference, as key components in heavy trucks, serve to connect the engine and transmission. Formability and mechanical performance control of such components should be taken into consideration. In this work, an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting. The role of local loading on microstructure and mechanical property at thick-walled positions was investigated. Furthermore, the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed. The results showed that at the thick-walled positions, local loading not only helped eliminate the solidification defects, but also refined the microstructure including α-Al grains and secondary dendrite arm spacing. With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa, microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained. After T6 heat treatment, the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa, respectively, owing to the formation of spherical eutectic Si phases and nano-sized β'', Q and S precipitates.

Uncommon Cold-Rolling Faults in an Fe–Mn–Si–Cr Shape-Memory Alloy

The paper analyzes the occurrence of evenly spaced cracks on the surface of lamellar specimens of Fe-28Mn-6Si-5Cr (mass %) shape-memory alloy (SMA), during cold rolling. The specimens were hot rolled and normalized and developed cold rolling cracks with an approximate spacing of about 1.3 mm and a depth that increased with the thickness-reduction degree. At normalized specimens, X-ray diffraction patterns revealed the presence of multiple crystallographic variants of brittle α′ body-bcc martensite, which could be the cause of cold-rolling cracking. Both normalized and cold-rolled specimens were analyzed using scanning electron microscopy SEM. SEM micrographs revealed the presence of several crystallographic variants of α′-body-centered cubic (bcc) and ε hexagonal close-packed (hcp) martensite plates within a γ-face-centered cubic (fcc) austenite matrix in a normalized state. High-resolution SEM, recorded after 25% thickness reduction by cold-rolling, emphasized the ductile character of the cracks by means of an array of multiple dimples. After additional 33% cold-rolling thickness reduction, the surface of crack walls became acicular, thus revealing the fragile character of failure. It has been argued that the specimens cracked in the neutral point but preserved their integrity owing to the ductile character of γ-fcc austenite matrix.

Effect of Al–Fe–Mn–Si particle characteristics on the growth morphology and corrosion resistance of anodic oxide film on AA 3003 aluminium alloy

This study examines the impact of Al–Fe–Mn–Si particle characteristics in AA3003 alloy on the morphology and resistance of anodic oxide films against corrosion. The results show that low-silicon-content Al–Fe–Mn–Si particles oxidise simultaneously with the matrix to form a discontinuous porous oxide film, and complex small pores are formed in the porous layer; although high-silicon-content Al–Fe–Mn–Si particles have the same oxidation rate as the alloy matrix, the growth of the oxide film is hindered by unoxidised particles in the porous layer due to the influence of particle size and chemical composition, resulting in uneven growth of the oxide film and ultimately causing defects such as enlarged pores and cracks. A mechanism model for Al–Fe–Mn–Si particles affecting the morphology of oxide film growth was established. Electrochemical test results show that compared with the oxide film of the high-silicon-content alloy, the oxide film of the low-silicon-content alloy has better corrosion resistance performance, with a corrosion potential of −0.512V (compared with −0.836V for the high-silicon alloy) and a corrosion current density of 3.34 × 10−8A/cm2 (compared with 9.614 × 10−7 A/cm2 for high-silicon alloy). The barrier layer attained an elevated impedance value and exhibited self-repairing capabilities.

Investigation of the interface precipitation on α-Al(Fe,Mn)Si particles in Al–Fe–Mn–Si–Mg–Cu alloy

The effects of particles on precipitation reactions in aluminum alloy have been widely unknown. Al–Fe–Mn–Si–Mg–Cu alloy strengthened with uniformly distributed Al(Fe,Mn)Si nanoparticles was successfully produced in this study. The alloy was then characterised using high-resolution scanning transmission electron microscopy (HRTEM), to provide a fundamental insight into the interface precipitation. Interfacial precipitations of several tens of nanometers in size was formed after aging, which were found to be Al5Cu6Mg2 and Si phases. The results demonstrated that the facetted α-Al(Fe,Mn)Si particles had a significant influence on precipitation adjacent to the α-Al(Fe,Mn)Si/Al interfaces. Semi-coherent α-Al(Fe,Mn)Si/Al interfaces were revealed to have periodically spaced misfit dislocations that are generally considered to be beneficial to heterogeneous precipitation. They not only reduce nucleation energy barriers but also act as short-circuit diffusion paths to accelerate growth rates by transporting solute atoms and vacancies.

Effect of Cerium Addition on the Microstructure and Shape Memory Properties of Austenitic Fe–Mn–Si–Cr–Ni Alloys

The addition of rare earth elements, such as cerium, to austenitic Fe–Mn–Si‐based shape memory alloys has been shown to improve both corrosion resistance and shape recovery. However, the mechanisms underlying the effect of Ce on shape recovery are still unclear. This study investigates the influence of the addition of small amounts of Ce (0.18, 0.42, and 0.96 wt%) on the microstructure and shape recovery of an austenitic Fe–13.50Mn–3.98Si–9.54Cr–4.51Ni alloy. Ce additions induce the formation of a large number of Ce‐rich particles, which act as austenitic grain refiners. Both grain refinement and the formation of Ce‐rich particles contribute to the strengthening of the matrix at 0.42 wt% Ce addition. In addition, Ce additions alter the MS temperature, which increases with Ce additions. Total shape recovery improves with 0.18 and 0.42 wt% Ce additions, but decreases with 0.96 wt% Ce addition. The beneficial effect of Ce addition in improving the shape recovery of the austenitic Fe–Mn–Si–Cr–Ni alloy is related to the enhancement of the elastic shape recovery component of the total shape recovery. However, the shape memory recovery due to the shape memory effect always decreases with the increase of the Ce content.

Elucidating deformation pathways and interface characteristic of self-accommodated dual γ/ε phase microstructure in Fe–Mn–Si–Al alloy

There has been an intense scientific interest in investigating the phenomenon of deformation-induced ε-ε martensite (hcp) interaction owing to the thermodynamically paradoxical reverse transformation and mechanical twinning. In this study, detailed transmission electron microscopy has been employed to examine the crystallographic orientation relationship, phase stability and boundaries between the intersection phases on the ε-ε intersections in a 10% tensile deformed Fe–30Mn–4Si–2Al alloy. The transformation/twinning scheme is systematically summarized initiating from the austenite matrix (γ) and two deformation-induced ε-martensite variants. It involves diverse intersection reactions: mechanical ε-twins, a 90°-rotating γ-phase from the γ matrix (γR), and 90°-rotate ε-phase re-transformed from the intersection γ. All these phases share a common 〈101〉γ || <21¯1¯0>ε axis that is equivalent to the intersection axis of the crossing {111}<12¯1>γ shears and interrelated with rotational angles with respect to the axis. Electron diffraction, coupled with stereographic analysis, revealed the distinct orientation relationships between γ–ε and γR–ε phases. The boundaries between the intersection γR and neighboring ε-phase are inclined from the corresponding {111}γ||{101¯1}ε planes. By means of the phenomenological theory of martensite crystallography (PTMC), the inclination of the boundary is rationalized by considering the lattice-invariant shear on the double {111}γ plane inside the intersection γ to satisfy the invariant plane condition of the boundary.

In-situ studies of primary nucleation and growth of the cubic Al19Fe4MnSi2 phase in an Al–Fe–Mn–Si metallic glass

The crystallization process of amorphous/glassy alloys below the glass transition temperature when the diffusion processes are hampered is of great interest for study. Here, we measured the growth rate of a crystalline phase with a complex cubic structure in the Al–Fe–Mn–Si metallic glass near the crystallization temperature in-situ by using transmission electron microscopy. We estimated the effective diffusion coefficient that is likely related to the slowest diffusing element (Mn). The results are compared with the crystallization of different other amorphous/glassy alloys considering the reduced crystallization temperature. Notwithstanding of the compositional difference from the matrix growth of the crystalline phase is significantly faster than can be estimated from the corresponding diffusion coefficients found for pure Al and AlFe compound.

Adapting Fe–Mn–Si–Cr shape memory alloy for laser powder bed fusion by adjusting the Mn content

Shape memory alloys (SMA) are functional materials exhibiting the shape memory effect. Conventional standard manufacturing technologies for shape memory alloys include melting, casting, and forming. These often require additional machining steps to achieve the final component shape, limiting the geometric design. The production of SMAs using additive manufacturing technologies opens up new possibilities, but research has been limited, especially for iron-based SMAs. The present study investigated whether an iron-based SMA alloy powder suitable for the additive manufacturing process can be produced via atomization and subsequently 3D printed with laser powder bed fusion (PBF-LB/M). Two FeMnSi SMAs with varying manganese contents of 23.6% and 28.5% were successfully atomized and laser processed. The effect of the manganese content on the shape memory characteristics was investigated by means of dilatometry. A 5 wt% change in manganese content was found to impact the onset of the keyhole fusion mode for PBF-LB/M as well as the resulting shape memory characteristics. Reduced manganese content is shown to enhance the shape memory effect of FeMnSi.

High‐Temperature Oxidation Behavior of Medium‐Manganese Austenitic Steel

The high‐temperature oxidation behavior of medium‐manganese austenitic steel is investigated. The double‐layered oxide scale is formed in the investigated samples. The outer oxide layer consists of (Fe,Mn)‐rich oxides, while the inner oxide layer is mainly composed of AB2O4 spinel oxides. When the oxidation temperature is 800 °C, a region composed of oxide and ferrite is formed in the substrate surface layer. When the oxidation temperature is 900 and 1000 °C, there is no such region observed in the substrate surface layer. Although the content of Al in the Fe–Mn–Al sample and the content of Si in the Fe–Mn–Si sample are relatively lower than the content of Cr in the Fe–Mn–Cr sample, the oxidation resistance of the Fe–Mn–Al and Fe–Mn–Si samples is still better than that of the Fe–Mn–Cr sample. The oxidation resistance of the Fe–Mn–Cr–Al and Fe–Mn–Cr–Si samples is also better than that of the Fe–Mn–Cr sample. The addition of Al and Si can improve the oxidation resistance of the Fe–Mn–Cr sample. Besides, the oxidation resistance improvement effect of adding Si to the Fe–Mn–Cr sample is better than that of adding Al to the Fe–Mn–Cr sample.

Effect of cooling rate on the final microstructure and tensile property in an Fe–Mn–Si–C-based multiphase TRIP steel

The effect of cooling rate on the formation of the final microstructure and the tensile property was studied in Fe–Mn–Si–C-based multiphase steel. Three different cooling rates of 5 °C/s, 10 °C/s, and 30 °C/s (CR5, CR10, and CR30) were applied from 800 °C to 400 °C and then the specimens held at 400 °C for 30 min. EPMA, EBSD, and TEM analyses clarified the constituent phases' volume fractions and the mechanical stability of retained γ. Appling a faster cooling led to a remarkable increase of tensile properties without a loss of elongation. This increase was accompanied by a higher fraction of bainite as the cooling rate increased All the specimens showed a similar fraction and mechanical stability of γ. In-situ tensile EBSD experiment revealed the accelerated deformation-induced martensite transformation (DIMT) in the faster cooling rate condition. The increased flow stress from a larger bainite fraction brought faster DIMT kinetics and improves tensile properties. This study provides a detailed understanding of the influence of cooling rate on microstructural evolution and tensile properties.