Fe Mn Si Cr Ni Alloy Research Articles

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.

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.

Improvement of the Oxidation Resistance of FeMnSiCrNi Alloys with a Pre-Oxidation Treatment

Improvement of the Oxidation Resistance of FeMnSiCrNi Alloys with a Pre-Oxidation Treatment

Ferritic layers formation mechanism during oxidation of FeMnSiCrNi alloys: Effect of temperature and influence on oxidation behavior

Ferritic layer formation occurs after oxidation in Mn-rich austenitic alloys. It has significant effects on high-temperature oxidation resistance, but a better understanding of its formation is needed to control these effects. Thus, two FeMnSiCrNi alloys were exposed to six temperatures between 675 and 800 °C for 100 h. A relationship between mass variation and ferrite thickness was revealed, as Mn and Cr depletion occurred due to the Mn2O3/MnCr2O4 formation. Thermodynamic calculated phase diagrams indicated ferrite stability at high temperatures, affecting oxidation resistance. Finally, the Mn concentration profile changes during oxidation were studied with DICTRA analyses to explain the ferritic layer growth. By describing the growth and characteristics of this layer, the study can serve as a starting point for future investigations into designing more oxidation-resistant FeMnSiCrNi alloys.

Correlation between shape memory effect and density of annealing twin boundary in an FeMnSiCrNi alloy during special heat treatments with different parameters

It remains unclear whether a negative dependence of shape memory effect (SME) still exists on the density of annealing twin boundary (ATB) in FeMnSi-based alloys during special heat treatments without optimal parameters. To address this issue, the evolutions of grain size and martensite amount in an Fe-14.5Mn-5.5Si-8.2Cr-5.2Ni-0.016C alloy were investigated in addition to the evolution of ATB density during the special heat treatments, i.e. training and thermomechanical treatment with different annealing temperatures. The results showed that the SME still showed a strong negative dependence on the ATB density independent of the special heat treatments. An obvious positive dependence of SME existed on the density of low angle grain boundary concomitant with the reduced ATB density. No obvious correlation between the SME and the grain size existed when the pre-deformation was rather lower (<4%). Larger grain size and less pre-existing martensite were conducive to realizing larger recovery strains.

Aligning Cr23C6 particles to improve shape memory effect in an FeMnSiCrNi alloy by ageing after pre-deformation at different temperatures

Our previous work had shown that shape memory effect (SME) of FeMnSiCrNi alloys can be remarkably improved by aligning Cr23C6 particles through introducing directional interfaces of austenite and deformation-induced martensite at room temperature before ageing. In present paper, we investigated the effects of ageing after pre-deformation at 203 K and room temperature on the precipitation of aligned Cr23C6 particles in an Fe15.3Mn5.8Si8.5Cr4Ni0.2C alloy to further improve the SME. The results showed that regardless of the deformation temperature, the SME improvement by the ageing was obviously higher after pre-deformation by 12% than 5% due to more aligned Cr23C6 particles. The ageing did not improve the SME more obviously after 12% pre-deformation at 203 K than room temperature although the number of directional interfaces between the austenite and martensite was higher. This abnormality could be rationalized by the more dislocations after pre-deformation at room temperature and concurrent comparable number and size of aligned Cr23C6 particles.

Formation of Subsurface Ferritic Layers During Oxidation of Femnsicrni Alloys Due to Manganese Depletion and Their Influence on the Oxidation Resistance of These Alloys

Formation of Subsurface Ferritic Layers During Oxidation of Femnsicrni Alloys Due to Manganese Depletion and Their Influence on the Oxidation Resistance of These Alloys

Effects of silicon and manganese content on the oxidation behavior of FeMnSiCrNi alloys and the correlation between Mn-depleted zone, surface roughness and oxidation resistance

Manganese and silicon effect on high-temperature cyclic oxidation was evaluated in three austenitic shape-memory FeMnSiCrNi alloys, including a novel high-silicon alloy (Fe-17Mn-8Si-10Cr-4Ni-NbC). Mass variation, Mn-depleted zone and metal/oxide interface roughness analyses were used to study the oxidation behavior. Renewed mass gain after spallation was observed for Fe12Mn5Si and Fe17Mn5Si alloys, while Fe17Mn8Si continuously lost mass, associated with low metal/oxide interface roughness and the ferritizing potential of Si. Low manganese availability led Fe12Mn5Si to suffer internal oxidation and iron oxide formation. Here, neither increasing silicon nor reducing manganese increased cyclic oxidation resistance of the alloys.

Initial stages of FeMnSiCrNi shape memory stainless steels oxidation mechanism at 800 °C

FeMnSiCrNi alloys form Mn-rich oxide and Mn/Cr spinel at high temperature. However, studies on the oxidation mechanism are still incipient. Thus, in order to understand the initial oxidation stages of the alloy Fe-17Mn-5Si-10Cr-4Ni-VC at 800 °C, up to 24 h, the oxide scale has been characterized by XR-Diffraction, Raman spectroscopy and TEM-ASTAR. Ferrite expansion during cooling was detected and a new oxidation mechanism was proposed, with simultaneous Mn2O3 (externally) and Mn/Cr spinel (internally) formation since the beginning of oxidation, as also discontinuous Cr2O3 surrounded by spinel. The formation of tetragonal-(Mn,Cr)3O4 was also reinterpreted, highlighting the importance of Mn-diffusion on MnCr2O4.

Fe–Mn–Si–Cr–Ni based shape memory alloy: Thermal and stress-induced martensite

The determining role of C- and Si-content on the shape memory effect of Fe–Mn–Si–Cr–Ni alloys, where Si was partly replaced by Co. In this regard, three alloys, Fe–15Mn–5Si–8Cr–5Ni, Fe–15Mn–5Si–8Cr–5Ni-0.1C, and Fe–15Mn–3Si–8Cr–5Ni-0.1C–2Co were designed to simultaneously study the shape memory effect and mechanical properties in relation to the microstructure. The microstructure of the alloys after cold rolling and annealing was analyzed by EBSD and X-ray diffraction techniques. The results indicated that grain size and the addition of C influenced the shape memory effect of Fe–Mn–Si–Cr–Ni-based memory alloy. With the increase of grain size, the annealing twin density was decreased, reducing the constraint on phase transformation of γ-austenite to ε-martensite. Furthermore, the austenite stability was decreased, such that the martensite-content was increased, and then reduced the shape memory effect of the experimental alloy. With the addition of C, the content of thermally-induced martensite was reduced, and the probability of stress-induced transformation of martensite to obtain α′-martensite was reduced, with consequent enhancement of the shape memory effect for the experimental steel. Additionally, the strength of parent phase was enhanced by the addition of C, and the plastic deformation by slip during stress-induced martensite was minimized, leading to low α′-martensite content and promotion of reversal of stress-induced martensite.

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.

Fabrication of Ferrite-Coated Magnetic Fe–Mn–Si–Cr–Ni Alloy Utilizing Selective Oxidation of Mn Element

The development of magnetic properties extends application fields of Fe–Mn–Si-based shape memory alloys (SMAs) into the field of electromagnetic sensors and actuators. In the previous studies, magnetic Fe–Mn–Si-based shape memory ribbons have been prepared by the melt-spinning technique. However, the melt-spinning technique could only obtain 2-D thin materials. In this paper, a ferrite-coated Fe–18.81Mn–5.61Si–9.31Cr–5.36Ni bulk shape memory material, exhibiting both magnetic and shape memory functions, was fabricated by means of the oxidation at 1173 K for different times. The ferritic layer was depleted in the Mn element due to the selective oxidation of the Mn element, and its growth behavior followed the parabolic law. Furthermore, we prepared not only ferrite/austenite/ferrite sandwich sheets but also matrix at ferrite core–shell wires in the case of ferrite-coated Fe–18.81Mn–5.61Si–9.31Cr–5.36Ni alloy. The shape recovery ratio of sandwich sheets decreased to 74.1% from 78.3% of the ferrite-free state while their saturation magnetization increased to 7.8 emu/g. The shape recovery ratio of core–shell wires decreased to 54.8% from 78.3% of the ferrite-free state with increasing the saturation magnetization to 36.2 emu/g. For both sandwich sheets and core–shell wires, there is a tradeoff relationship between shape memory effect (SME) and saturation magnetization. Accordingly, it is necessary to strike a balance between their shape memory and magnetic properties according to engineering applications.

High temperature oxidation resistance improvement in an FeMnSiCrNi alloy by Mn-depletion under vacuum annealing

FeMnSiCrNi alloys present good properties, although the oxidation resistance at high temperatures is limited by high manganese amount. Thus, the present study evaluated a vacuum annealing treatment on an Fe-17Mn-5Si-10Cr-4Ni-VC alloy as a surface modification method, aiming to improve oxidation resistance. The treatment was performed during 10 h at 1100 °C, generating an external ferrite layer of 170 μm in thickness (manganese decreased to 2 wt%). Oxidation tests at 800 °C up to 24 h in untreated and vacuum treatment demonstrated that heat treatment decreased the mass gain rate in two orders of magnitude through more protective oxide formation.

Anomalous cyclic oxidation behaviour of an Fe-Mn-Si-Cr-Ni alloy - A finite element analysis

In previous research, an FeMnSiCrNi alloy presented anomalous behaviour during cyclic oxidation and gained mass after mass loss by spallation. Research clarified this phenomenon, but no stress analysis had been examined. This study investigates this anomalous behaviour using finite element analysis. FeMnSiCrNi alloy oxidation generates a Mn-depleted zone (ferrite) between the substrate (austenite) and oxide layer, and models containing austenite-ferrite-oxide demonstrated that increasing ferrite thickness and roughness (metal/oxide interface) decrease oxide layer stress, helping to comprehend why the alloy stops losing mass. The main cause, increasing roughness, was derived from ferrite plastic deformation and relates to austenite-ferrite thermal expansion mismatch.

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.

Role of carbon in improving the shape memory effect of Fe–Mn–Si–Cr–Ni alloys by thermo-mechanical treatments

To clarify the role of carbon in improving the shape memory effect of Fe–Mn–Si-based shape memory alloys by thermomechanical treatments, we investigated the effect of optimum thermomechanical treatments on shape memory effect and microstructures of Fe–14Mn–5Si–8Cr–4Ni and Fe–14Mn–5Si–8Cr–4Ni–0.12C alloys. The Cr23C6 particles in optimum thermomechanical-treated Fe–14Mn–5S–8Cr–4Ni–0.12C more effectively prevented collisions between stress-induced ϵ martensite bands than the residual α′ martensite in optimum thermomechanical-treated Fe–14Mn–5Si–8Cr–4Ni. This result is attributed to the thinner width of stress-induced ϵ martensite bands in optimum thermomechanical-treated Fe–14Mn–5S–8Cr–4Ni–0.12C compared to optimum thermomechanical-treated Fe–14Mn–5Si–8Cr–4Ni. In addition, the Cr23C6 particles formed at more sites and provided more obstacles as compared with the residual α′ martensite. Accordingly, the recovery strain of Fe–14Mn–5Si–8Cr–4Ni–0.12C was higher than that of Fe–14Mn–5Si–8Cr–4Ni. It is concluded that carbon addition is beneficial to further improving the shape memory effect of Fe–Mn–Si-based shape memory alloys by thermomechanical treatments.

Shape Recovery in Stainless FeMnSiCrNi(-Co) SMA Processed by ECAE

Stainless shape memory steel presents reasonable shape recovery but lower than the traditional NiTi shape memory alloys (SMA). However, recent results have shown that the shape recovery could be improved by decreasing the austenitic grain size. The present work describes the influence of the austenitic grain size on the shape recovery in stainless shape memory steel deformed by equal channel angular extrusion (ECAE) using a die intersection angle of 120o. Two alloys, FeMnSiCrNi and FeMnSiCrNiCo, were deformed by 1 ECAE pass and then they were compared in the deformed state; deformed and annealed in different temperatures for 1 h, resulting different grain sizes. Both alloys were evaluated by compression tests and the results shows an increase in total shape recovery related to grain size decrease. The best total shape recovery was 73% after a pre-strain of 4% for FeMnSiCrNi alloy.

Influence of VC Precipitation on the Shape-Memory Effect and Corrosion Resistance on an Fe–Mn–Si–Cr–Ni Alloy

The shape-memory effect (SME) and corrosion resistance of an Fe-20Mn-5Si-10Cr-5Ni- 0.7V-0.2C alloy, before and after aging, were investigated. The results showed that VC precipitation and bending temperatures obviously affect the alloy’s SME. Nearly perfect SME (90.2% of initial 4% bend) was achieved when the 2h aged sample was deformed at 223K. At the meantime, the electrochemical impedance spectroscopy (EIS) showed that the alloy, aged for 2h to 4h, exhibited the worst corrosion resistance in the research system related with the fine VC precipitates. The morphology and distribution of VC were observed by SEM.

The Influence of Phase Transformation Cycling on Improving of Plasticity and Microstructure of Fe-14Mn-4Si-8Cr-4Ni Alloy

The influence of phase transformation cycle times on the plasticity and microstructure of FeMnSiCrNi alloy was researched in this paper. The results show that phase transformation cycling can significantly improve the plasticity of the alloy. Plasticity is improved with the increase of cycles. The elongation gets to 87.6% after 5 cycles, it increases 150% compared with non-treated. The more cycle times, the grain is smaller. During the inverse transformation the second phase directional precipitation significantly harden austenite and improve the reversibility of stress-induced martensite. Due to interaction of the second phase strengthening and grain refinement, the plasticity and strength of alloy are both increased significantly. This method provides a new way for the realization of transformation superplasticity.

Factors affecting recovery stress in Fe–Mn–Si–Cr–Ni–C shape memory alloys

The effects of the heating temperature, the carbon content, the amount of pre-strain, the annealing temperature, and the conventional training on the recovery stresses at room temperature of cold-drawn Fe–Mn–Si–Cr–Ni–C shape memory alloys were studied. The results showed that the addition of carbon or the refining of grains could more significantly enhance the recovery stress than the conventional training. The recovery stress of a cold-drawn Fe–Mn–Si–Cr–Ni alloy with 0.18%C could reach 565MPa only after annealed at 1023K. Its recovery stress was only improved to 452MPa after it was subjected to annealing at conventional temperature 1373K and then four cycles of the conventional training. The dominating factors affecting the recovery stress were the amount of the plastic deformation and that of the martensitic transformation induced by the recovery stress in cooling, not the recovery strain under no constraints.