Fe Ni Mn Alloys Research Articles

Structural Change in Co–Cr–Fe–Mn–Ni Alloys upon Variation in Mn and Fe Concentrations

Structural Change in Co–Cr–Fe–Mn–Ni Alloys upon Variation in Mn and Fe Concentrations

Syngas production from phenolic pollutants via a series of hydroxylation, ring cleavage, and aqueous-phase reforming catalyzed by a hydrotalcite-supported Fe–Mn–Ni alloy

A trifunctional catalyst facilitating a series of hydroxylation, oxidative ring opening, and aqueous-phase reforming reactions was developed to convert phenolic wastewater into syngas.

Composition stability of single fcc phase in Cr–Fe–Mn–Ni alloys: First-principles prediction and experimental validation

The relative phase stability of fcc and bcc Cr–Fe–Mn–Ni alloys has been investigated using a combination of density functional theory, cluster expansion (CE), and Monte Carlo (MC) simulations. The MC simulations for fcc and bcc Cr–Fe–Mn–Ni alloys performed using the CE models enabled computing the Gibbs free energies of formation of 1767 fcc and bcc alloys in the whole range of compositions of each element and analyzed as a function of temperature. In order to determine regions of stability of single fcc/bcc structures and atomic fractions of these phases in two-phase regions, we constructed the thermodynamic databases (TDBs) derived from MC simulations with their application in the OpenCalphad calculations. The results obtained using this approach are in qualitative agreement with the available experimental data from the literature and the experiments performed within this work for the samples of [CrFeMn]100−xNix (x = 20, 25 and 35 at.%) alloys synthesized using arc-melting and annealed at 1273 K for 48 h. The analysis of fcc fractions of the near-equiatomic alloy compositions has enabled the identification of the alloys that are predicted to be single fcc phase for a wide range of temperatures.

Significance of Mn concentration on aging behavior, microstructure evolution and mechanical properties of Fe–Ni–Mn alloys

Fe–Ni–Mn alloys, are ultra-high-strength steels, with suitable ductility and age-hardenability in the solution annealed (SA) condition. However, they suffer from grain boundary embrittlement after aging at ∼480OC, when Mn content goes beyond a specific value. This study was conducted to investigate systematically the effects of the Mn concentration on the microstructural evolution, aging behavior, and the resulting mechanical properties of Fe–10Ni–xMn alloys containing 3.5, 6 and 9Mn wt.%. Samples containing 3.5 and 6 wt.% Mn showed age-hardenability during aging and higher Mn content resulted in a higher hardness value which in turn showed higher strength. The Mn content of about 9 wt.% led to the stability of the austenite phase at room temperature (RT). The results showed that although age-hardening did not occur in this microstructure, a good combination of strength and ductility was achieved. Studying the effects of Mn content in a wide range, resulted in different properties by introducing the proper chemical composition and the preferred heat treatments in this type of alloys, which could be age-hardenable, easy to fabricate, and low-cost.

The autocatalytic evolution of martensitic microstructure

This work considers the autocatalytic spread of the martensitic transformation throughout the austenite grains in FeNiC and FeNiMn alloys. Formal descriptions were reviewed. The microstructural path concept was re-introduced. The model’s analysis of scale factors reiterated the importance of the martensite–austenite interaction. We compared the initial heterogeneous martensite nucleation in a polycrystalline FeNiC with the nucleation in a Fe30Ni particulate alloy. A cluster of tetrakaidecahedral austenite grains might be a reasonable choice to describe the martensite spread in the FeNiC.

Insights from an OKMC simulation of dose rate effects on the irradiated microstructure of RPV model alloys

This work studies the defect features in a dilute FeMnNi alloy by an Object Kinetic Monte Carlo (OKMC) model based on the "grey-alloy" method. The dose rate effect is studied at 573 K in a wide range of dose rates from 10−8 to 10−4 displacement per atom (dpa)/s and demonstrates that the density of defect clusters rises while the average size of defect clusters decreases with increasing dose rate. However, the dose-rate effect decreases with increasing irradiation dose. The model considered two realistic mechanisms for producing <100>-type self-interstitial atom (SIA) loops and gave reasonable production ratios compared with experimental results. Our simulation shows that the proportion of <100>-type SIA loops could change obviously with the dose rate, influencing hardening prediction for various dose rates irradiation. We also investigated ways to compensate for the dose rate effect. The simulation results verified that about a 100 K temperature shift at a high dose rate of 1 × 10−4 dpa/s could produce similar irradiation microstructures to a lower dose rate of 1 × 10−7 dpa/s irradiation, including matrix defects and deduced solute migration events. The work brings new insight into the OKMC modeling and the dose rate effect of the Fe-based alloys.

Integrated High-Throughput and Machine Learning Methods to Accelerate Discovery of Molten Salt Corrosion-Resistant Alloys.

Insufficient availability of molten salt corrosion‐resistant alloys severely limits the fruition of a variety of promising molten salt technologies that could otherwise have significant societal impacts. To accelerate alloy development for molten salt applications and develop fundamental understanding of corrosion in these environments, here an integrated approach is presented using a set of high‐throughput (HTP) alloy synthesis, corrosion testing, and modeling coupled with automated characterization and machine learning. By using this approach, a broad range of Cr—Fe—Mn—Ni alloys are evaluated for their corrosion resistances in molten salt simultaneously demonstrating that corrosion‐resistant alloy development can be accelerated by 2 to 3 orders of magnitude. Based on the obtained results, a sacrificial protection mechanism is unveiled in the corrosion of Cr—Fe—Mn—Ni alloys in molten salts which can be applied to protect the less unstable elements in the alloy from being depleted, and provided new insights on the design of high‐temperature molten salt corrosion‐resistant alloys.

Influence of Electron Beam Treatment on the Defect Substructure of a High-Entropy Co–Cr–Fe–Mn–Ni Alloy

Influence of Electron Beam Treatment on the Defect Substructure of a High-Entropy Co–Cr–Fe–Mn–Ni Alloy

Temperature-Dependent Irradiation-Induced Clustering in a Fe–Mn–Ni Alloy

Temperature-Dependent Irradiation-Induced Clustering in a Fe–Mn–Ni Alloy

Influence of plastic deformation on the microstructural and magnetic properties of some Fe-based alloys

We report the morphological and magnetic properties of deformation-induced martensite characteristics in the austenite phase of Fe69Ni27Mn4 and Fe67Ni27Mn4Zn2 (wt %) alloys after 30% plastic deformation. Scanning electron microscopy (SEM) and also physical property measurement system (PPMS) facilities were applied to investigation to clarify the deformation-induced martensite characteristics from morphological and magnetic points of view. Scanning electron microscope observations showed elongated deformation-induced martensite morphology in the austenite phase of the examined alloys. Additionally, two alloys exhibited typical ferromagnetism in their martensite phase. The saturation magnetization (Msat) was found to be firstly increased and then decreased with increasing temperature. We found that the % Zn addition shifts the Curie temperature (Tc) of Fe–Ni–Mn alloys to higher temperatures. The largest Msat (~ 27 emu·g−1), the Hc (~ 26 Oe), and Tc (~ 248) were obtained for the Fe–Ni–Mn–Zn alloy with a mixed configuration of bcc and fcc phases.

High Entropy and Sluggish Diffusion "Core" Effects in Senary FCC Al-Co-Cr-Fe-Ni-Mn Alloys.

Relative role of enthalpy and entropy in the stabilization of senary FCC Al-Co-Cr-Fe-Ni-Mn high entropy alloys was investigated via a high throughput combinatorial solid-to-solid diffusion couple approach. Many off-equiatomic compositions of FCC AlpCoqCrrFesNitMnu were generated by the diffusing Al and Ni in equiatomic Co20Cr20Fe20Ni20Mn20 alloy, i.e., the Al48Ni52 vs Co20Cr20Fe20Ni20Mn20 diffusion couple, annealed at 900°, 1000°, 1100°, and 1200 °C. Above 1000 °C, the solubility limit of Al in off-equiatomic AlpCoqCrrFesNitMnu alloy was determined to be higher than the solubility limit of Al in equiatomic AlxCoCrFeNiMn alloy. Compositions corresponding to the highest solubility limit of Al in off-equiatomic AlpCoqCrrFesNitMnu alloy exhibited a lower free energy of mixing, i.e., higher thermodynamic stability, than equiatomic AlxCoCrFeNiMn compositions, at 1100 °C and above. Therefore, the role of enthalpy was estimated to be significant in achieving higher thermodynamic stability in off-equiatomic alloys, since they always have lower entropy of mixing than their equiatomic counterparts. The magnitude of interdiffusion coefficients of individual elements in Al-Co-Cr-Fe-Ni-Mn alloys were compared to the interdiffusion coefficients in relevant quinary, quaternary, and ternary solvent-based alloys. Interdiffusion coefficients were not necessarily lower in FCC Al-Co-Cr-Fe-Ni-Mn alloys; therefore no sluggish diffusion was observed in FCC HEA, but diffusion of individual elements in BCC Al-Co-Cr-Fe-Ni-Mn alloy followed the sluggish diffusion hypothesis except for Ni. All compositions in the FCC Al-Co-Cr-Fe-Ni-Mn alloy were observed to comply with existing empirical single phase formation rules in high entropy alloys.

Microstructure, Mechanical Properties, and Sliding Wear Behavior of Oxide-Dispersion-Strengthened FeMnNi Alloy Fabricated by Spark Plasma Sintering

The face-centered-cubic (fcc) CoCrFeMnNi high-entropy alloy suffers from low strength and wear resistance at ambient temperature. Herein, we developed a strategy to overcome the strength/ductility trade-off and simultaneously increase the wear resistance via the in situ formation of uniformly dispersed Mn3O4 nanoparticles in an ultrafine-grained fcc FeMnNi matrix. The obtained equiatomic FeMnNi alloy exhibited a high yield strength of up to 912 MPa and an elongation of 19 pct. Grain boundary and oxide-dispersion-strengthened were found to be the main strengthening mechanisms. Ball-on-disk wear tests showed that the FeMnNi alloy had low wear rates in the order of 10−4-10−5 mm3/(N m) upon sliding against an alumina ball, and the wear mechanism changed from abrasive wear to oxidation and fatigue wear at high loads and sliding velocities. The presence of Mn3O4 nanoparticles hindered the severe plastic flow of the fcc matrix during sliding. The excellent combination of strength, ductility, and tribological performance of the present alloy renders it as a promising candidate for structural applications.

Influence of composition and as-cast structure on the mechanical properties of selected high entropy alloys

The paper investigates the influence of several alloying elements (Al, Mn, Cu, Ti and Si) and the typology of the as-cast structure on the mechanical properties of high entropy alloys. A theoretical criteria analysis was carried out on the Al–Cr–Cu–Fe–Mn–Ni, Al–Cr–Co–Fe–Ni–Ti, Al–Cr–Fe–Mn–Ni and Al–Cr–Cu–Fe–Mn–Ni–Si alloy systems to select appropriate compositions for application requirements. The alloys were prepared by induction melting and were cast in copper mold. As-cast samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction and mechanical analyses. The experimental results partially validated the criteria predictions. Alloys with higher Al content presented most predominantly BCC type phases. Ti and Cu were found enriched in the interdendritic area. Si influenced greatly the as-cast morphology of the dendrite structure. The substitution of Co with Mn generated a significant improvement of the mechanical properties. A composition-structure-properties correlation was described in the paper. The morphology of the as-cast structure had a strong impact on the final properties of the alloys. The Al–Cr–Fe–Mn–Ni alloy showed the best overall characteristics, with a hardness of 412 HV and a compressive strength of 895 MPa.

Nanoscale modulated structures by balanced distribution of atoms and mechanical/structural stabilities in CoCuFeMnNi high entropy alloys

We observed the nanoscale modulated structures in the homogenized CoCuFeMnNi and CoCu1.71FeMnNi high entropy alloys and the mechanical/nanostructural stabilities of modulated structures were studied by compressive deformation up to the true strain of 1.0. Constituent elements in CoCuFeMnNi and CoCu1.71FeMnNi alloys with dendrite structure comprised of the Cu-Mn rich interdendritic region and Co-Fe rich dendrite arms in the as-cast alloys appeared to be uniformly distributed on the microscopic scale after homogenization. One of the most interesting and unique observation in the homogenized alloys is the presence of nanoscale phase separation with no distinct separation or splitting of electron diffraction spots, suggesting two separated phases have the same structure and similar lattice constants. We propose that the reduction of lattice strain and interface energies through selective and balanced distribution of various atoms to minimize difference of lattice constants enabled nano-scale separation of the alloy into two FCC phases. The lattice strain energy decreased from 0.93 kJ mol−1 to 0.75 kJ mol−1 in CoCuFeMnNi and from 0.85 kJ mol−1 to 0.38 kJ mol−1 in CoCu1.71FeMnNi by separation into two phases with similar lattice constants. Both CoCuFeMnNi and CoCu1.71FeMnNi alloys exhibited rapid strain hardening up to the strain of 0.23 and then saturation of the flow stress. The initial rapid increase of hardening is attributed to the presence of nanoscale modulated two-phase structure.

The effect of dislocations on MnNi-rich clusters in self-ion irradiated FeMnNi alloy

The effect of dislocations on irradiation-induced MnNi-rich clusters in self-ion irradiated FeMnNi alloy was investigated using X-ray diffraction (XRD), nanoindentation, positron annihilation Doppler broadening spectroscopy (PADBS), and atom probe tomography (APT). The nanoindentation results showed that irradiation-induced hardening decreased with dislocation density increasing. The results of APT and PADBS revealed that high-energy Fe-ion irradiation generates high-density MnNi-rich clusters and large vacancy-type defects in irradiated FeMnNi alloy. Note that dense dislocations suppress the formation of large vacancy-type defects and MnNi-rich clusters. By analyzing the effect of dislocations on point defects (PDs), diffusion of Mn and Ni atoms, and nucleation of MnNi-rich clusters, we found that nucleation mechanism of MnNi-rich clusters is strongly dependent on the flux of PDs. However, high-density dislocations can facilitate to annihilate irradiation-induced PDs and cause the decline of defect-solute coupling fluxes, which are responsible for a reduction in number density and mole fraction of MnNi-rich clusters.

Revisiting Temperature and Magnetic Effects on the Fe-30 Wt Pct Ni Martensite Transformation Curve

This work revisits the relationship between the volume fraction of martensite and the transformed microstructure. This relationship is analyzed by considering that although thermodynamic principles determine the possibility of transformation, the size and arrangement of the martensite units over the austenite grains is determined by the local surroundings. The proposed equation for the transformation curve incorporates the probabilistic aspect of the initial transformation in a limited number of scattered austenite grains and autocatalysis. The validation of the model, already verified with data typical of FeC steels, FeNiC and FeNiMn alloys, is extended in this study to a transformation that exhibits microstructure diversity. Finally, we show that the model fits the transformation curves typical of “18Cr-8Ni” stainless steel; this finding demonstrates that the model is applicable to transformation curves characteristic of other systems due to a conceptualization based on the intrinsic aspects of martensite transformation in steels.

Understanding the deformation behavior of CoCuFeMnNi high entropy alloy by investigating mechanical properties of binary ternary and quaternary alloy subsets

Combinatorial approach has been employed to understand the deformation micro-mechanisms and strength evolution of FCC equiatomic CoCuFeMnNi high entropy alloy using equimolar subset alloys, judiciously unearthed by thermodynamic modelling using CALPHAD. A series of mechanical tests indicate absence of one-to-one correlation between entropy of mixing and mechanical properties for the alloys. Optimum combination of strength and ductility was observed in ternary equiatomic FeMnNi alloy, although quinary alloy exhibits the highest strength among all the four alloys. The deformation of all the alloys is dominated by octahedral slip as well as partial slip with the absence of deformation twinning. TEM investigation on the deformed samples reveals profuse dislocation activity. Strain rate sensitivity in the range of 0.005–0.008 and activation volume of 100–150 b3 indicate cross slip as the dominant operative mechanism for all the alloys. Nevertheless, quinary CoCuFeMnNi HEA manifests unique behavior by showing increase in strength even after long term annealing at 1273 K for 7 days. This is attributed to the presence of copper-rich nano-clusters in the alloy which undergo coarsening and partial dissolution thereby contributing to higher solid solution strengthening. Thus, the unique microstructure of the quinary CoCuFeMnNi HEA that can explore cluster strengthening and solid solution hardening manifests new vistas to design novel alloys for potential applications.

Effect of Magnetic state of Austenite on Martensitic transformation in Fe–Ni Alloys in High and Zero Magnetic Fields

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

The effect of alloying element Zn on magnetic properties of martensite phase in FeNiMn alloy

The effect of alloying element Zn on the characteristics of thermal induced martensite and magnetic properties of martensite phase were investigated with scanning electron microscopy (SEM) and Mössbauer spectroscopy characterization techniques. SEM observations revealed that the athermal martensitic transformation occurred with lath martensite morphology for different amount of Zn element. On the other hand Mössbauer spectroscopy showed that magnetic characteristic of martensite phase remarkably altered by increasing the amount of Zn element. The increased amount of Zn also causes the disappearance of the magnetization of the martensite phase.

Electrodeposition of multicomponent Co–Cr–Fe–Mn–Ni alloy

Abstract This work is focused on the initial realization of a multi-component coating deposition from the aqueous solution. The Coating composed of the elements Co-Cr-Fe-Mn-Ni was prepared by electroplating process. The chosen substrate was copper. The purpose of the work was to apply the high entropy alloy, which is defined as alloy with structure of a solid solution containing five or more elements in an approximately equal atomic ratio. The use of electrodeposition in this area is rare. The conditions of the plating process, the percentage of the metal ions and cohesion of the layers were studied. The morphology of the excluded coatings was monitored by scanning electron microscopy and their elemental composition was verified by the EDS analysis. The wear resistant features were examined approximately before and consequently also after the thermal resistance testing.