Fe Cr Ni Alloys Research Articles

Enhancing mechanical properties in Co-free medium-entropy alloys through multi-phase structural design

Pursuing cost-effective multicomponent alloys with superior properties has sparked interest in exploring Co-free alternatives. In this work, a notable structural evolution from a coarse columnar face-centered cubic (FCC) configuration to a refined dual-phase microstructure was observed in the as-cast Co-free equiatomic CrFeNi-based multicomponent alloys through the Al and Ti additions. The presence of L12 nanoprecipitates in the FCC matrix and multiscale nanoprecipitates in the body-centered cubic (BCC) matrix led to a substantial threefold increase in hardness and a ∼50% reduction in wear rate. The average friction coefficient (COF) was reduced to ∼0.6877. This alloy demonstrates exceptional compressive properties, with a yield strength of 1140 MPa, ultimate strength of 2569 MPa, and plastic strain of 38%. The yield strength is nearly tenfold higher than that of the CrFeNi alloy. These findings highlight the potential of multi-phase structural design as a promising strategy for the development of wear-resistant multicomponent alloys.

High-temperature deformation behaviour and processing map of near eutectic Al–Co–Cr–Fe–Ni alloy

The high-temperature deformation behaviour of near-eutectic high entropy alloy was studied at 800–1100 °C and 0.01–10 s−1. The microstructure of the as-cast alloy depicted a proeutectic L12 phase and epitaxially grown eutectic colonies of lamellar L12 and B2. Deformation temperature and strain rate played vital roles in defining the precipitation and deformation behaviour of the alloy. The lower-temperature deformed samples were characterized by extensive deformation twinning and strain accumulation. In contrast, high-temperature deformation led to uniform deformation with dynamic recrystallization, recovery, B2 lamellar fragmentation and B2 precipitation. The microstructure of the deformed samples corresponded well with the processing maps developed via dynamic materials model. The processing zones for the alloy were identified to be 800–950 °C and 10−2 – 10−1.25 s−1 as well as 925–1100 °C and 10−2 – 10−0.5 s−1. The critical material flow parameters displayed a complex relationship with temperature, strain rate and strain. In the studied temperature and strain rate regime, the critical strain rate was determined to be 0.1s−1. At strain rates above and below this value, the critical strain for recrystallization was higher. Within the studied temperature and strain rate regime, the near eutectic alloy displayed superior compressive strength and wider thermos-mechanical processing region than its eutectic counterpart.

Влияние добавок карбида и борида вольфрама на структуру и микротвердость эквиатомного CrFeNi-покрытия, сформированного короткоимпульсной лазерной наплавкой

A coating based on a single-phase medium-entropy CrFeNi alloy with a face centered cubic structure has good ductility, relatively high anti-corrosion properties, low cost, but insufficient strength for its widespread use. It is assumed that adding strengthening particles in the form of tungsten carbides and borides to the CrFeNi equiatomic coating will lead to an increase in its mechanical properties. This work studies the influence of tungsten carbide and boride additives on the structure and microhardness of a CrFeNi equiatomic coating. The coatings were formed by layer-by-layer short-pulse laser cladding with preplaced powder on a multifunctional laser installation equipped with a solid-state laser with a lamp pump based on an Nd:YAG crystal. The change in phase composition when adding strengthening particles was detected using X-ray diffraction analysis and transmission electron microscopy (TEM). Both methods confirmed the precipitation of Cr23C6 chromium carbide in the deposited coatings. TEM photographs indicate that the precipitated phase is distributed along the grain boundaries of the -solid solution. The study found that the addition of 6 wt. % WC and 3 wt. % WB increases the level of microhardness of the CrFeNi coating by 26 % (from 340±6 to 430±12 HV 0.025). This occurs due to the presence of Cr23C6, WC particles in the structure and possible microdistortions of the crystal lattice of the -phase as a result of doping with tungsten atoms released during the dissolution of tungsten borides and carbides in the process of high-temperature short-pulse laser heating.

Fe–Ni–Cr alloy matrix composite reinforced by superhard in-situ TiB2 produced through casting

ABSTRACT Fe–7.2Ni–16.2Cr–7Ti–3B (wt-%) composition was melted and cast into strips producing an in-situ TiB2 reinforcement within a stainless-steel matrix. The composite was characterised for microstructure and nanoindentation hardness. The microstructure consisted of in-situ formed particles of TiB2 and fine eutectic of austenite–borides. Superhigh nanoindentation hardness of 47.2 GPa was measured on TiB2 particles with 590.2 GPa elastic modulus while these values for the matrix were 6.95 and 277 GPa respectively.

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Unexpected deformation-induced martensitic phase transformations in Ni–Cr and Ni–Cr–Fe alloys

Deformation of Ni–Cr and Ni–Cr–Fe alloys has historically been understood to occur through dislocation slip, while deformation-induced martensitic transformations are believed to be suppressed by the high stacking fault energy (SFE). The present study challenges these longstanding beliefs with experimental and theoretical evidence of deformation-induced martensitic transformations in Alloy 625 and Ni–20Cr, respectively. Systematic investigations are conducted along the three principal grain orientations; experiments employ nanoindentation coupled with post mortem transmission electron microscopy (TEM) analysis, while molecular dynamics (MD) simulations are conducted in uniaxial tension. Experimental results reveal γ→ε and γ→ε→α′ martensitic transformations in Alloy 625 consistent with the Bogers-Burgers-Olson-Cohen (BBOC) intersecting shear mode. The orientation relationship is characterized as a distorted Shoji-Nishiyama OR between FCC/HCP and Kurdjumov-Sachs OR between FCC/BCC. By contrast, Alloy 690 does not exhibit martensitic transformations despite having a lower SFE than Alloy 625, due to Mo solute strengthening in Alloy 625. MD simulations reveal consistent transformation mechanisms across grain orientations, but orientation-dependent differences in Schmid factors and critical resolved shear stress affect the strain evolution and extent of the transformation. This study concludes that SFE alone may not comprehensively dictate whether deformation-induced martensitic transformations will occur; other factors such as free energy and strain rate also influence transformability.

Atomic Investigation of Corrosion Mechanism and Surface Degradation of Fe–Cr–Ni Alloy in Presence of Water: Advance Reactive Molecular Dynamics Simulation

Atomic Investigation of Corrosion Mechanism and Surface Degradation of Fe–Cr–Ni Alloy in Presence of Water: Advance Reactive Molecular Dynamics Simulation

Long-term corrosion behavior of FeCr(Al, Ni) alloys in O2 + H2O with KCl(s) at 600 °C: Microstructural evolution after breakaway oxidation

The microstructural evolution of the oxide scales formed on FeCr(Al,Ni) alloys after breakaway oxidation was studied in 5 % O2 + 20 % H2O + N2 (Bal) + KCl(s)/KCl(g) at 600 °C for 168, 1000 and 8000 h. The SEM/EDS, SEM/EBSD and XRD investigation show that all alloys experience breakaway oxidation and form multi-layered scales. Experimental results, thermodynamic modelling and kinetic simulations show that FeCrAl and FeCrNi alloys form chromium-rich spinel oxide in inward-growing scales which transform into a protective corundum-type oxide as the oxidation progresses, while FeCr alloy experiences fast oxidation and maintains a non-protective spinel oxide/internal oxidation after long exposures.

Laser‐Based Directed Energy Deposition Remanufacturing of Gray Cast Iron using Stainless Steel 316L and Inconel 625 Filler Materials

Directed energy deposition (DED) is identified as an ideal candidate for restoring damaged or worn cast iron components such as agricultural engine blocks, housings, and manifolds. While this laser‐based process offers superior control of the heat input compared to traditional arc‐based repair, gaseous porosity and brittle intermetallic structures reduce the strength and ductility of the fusion zone. Varying combinations of Fe–Ni–Cr alloys have found success in remanufacturing cast iron using laser‐based DED, but little attention has been given to the consequence of filler material composition and form, that is, wire versus powder. This study quantifies structural characteristics in cast iron repairs and offers microstructural and process‐specific insights to support these observations. With appropriate thermal conditions, up to 98.7% of the original tensile strength of gray cast iron may be achieved. These results point toward superior gray cast iron restoration using tunable laser‐based DED.

High-temperature corrosion model of Incoloy 800H alloy connected with Ni-201 in MgCl2–KCl heat transfer fluid

Abstract Long-term dipping corrosion experiments on Incoloy 800H (800H) in molten eutectic MgCl2–KCl salt at 1,073 K with and without connection with Ni-201 alloy were carried out. While connecting with Ni-201 alloy, the corrosion rate of 800H was 4.47 ± 0.26 mg·cm−2·day−1 (10−3.55±0.02 A·cm−2). However, the corrosion rate for the 800H that was not connected to the Ni-201 alloy was 3.00 ± 0.27 mg·cm−2·day−1 (10−3.71±0.04 A·cm−2). Therefore, Ni-201 alloy accelerates the corrosion rate of 800H in the molten MgCl2–KCl salt while connecting to each other. In addition, based on the calculation of Gibbs energy of Ni–Fe–Cr alloy and exchange current density of 800H in MgCl2–KCl salt, a new Tafel model was developed to predict the corrosion rate of 800H alloys. The corrosion rate calculated by the new model is 10−3.74 A·cm−2, which agrees with the experimental data.

An Experimental High-Throughput to High-Fidelity Study Towards Discovering Al–Cr Containing Corrosion-Resistant Compositionally Complex Alloys

Compositionally complex alloys hold the promise of simultaneously attaining superior combinations of properties, such as corrosion resistance, light-weighting, and strength. Achieving this goal is a challenge due in part to a large number of possible compositions and structures in the vast alloy design space. High-throughput methods offer a path forward, but a strong connection between the synthesis of an alloy of a given composition and structure with its properties has not been fully realized to date. Here, we present the rapid identification of corrosion-resistant alloys based on combinations of Al and Cr in a base Al–Co–Cr–Fe–Ni alloy. Previously unstudied alloy stoichiometries were identified using a combination of high-throughput experimental screening coupled with key metallurgical and electrochemical corrosion tests, identifying alloys with excellent passivation behavior. The alloy native oxide performance and its self-healing attributes were probed using rapid tests in deaerated 0.1-mol/L H2SO4. Importantly, a correlation was found between the electrochemical impedance modulus of the exposure-modified air-formed film and self-healing rate of the CCAs. Multi-element extended x-ray absorption fine structure analyses connected more ordered type chemical short-range order in the Ni–Al 1st nearest-neighbor shell to poorer corrosion resistance. This report underscores the utility of high-throughput exploration of compositionally complex alloys for the identification and rapid screening of a vast stoichiometric space.Graphical

Initial Study on Metal Dusting Behavior of Fe–Cr and Fe–Ni-Cr Alloys Under a Simulated Blast Furnace Operating Condition

Blast furnace ironmaking produces a reducing and carburizing atmosphere in the blast furnace which may lead to metal dusting. However, there is limited research on metal dusting under this particular atmosphere. This paper investigated metal dusting behaviors of ferritic Fe-(10, 20, 25)Cr and austenitic Fe-20Cr-(20, 33)Ni, Fe-25Cr-20Ni (wt.%) alloys at 550 and 650 °C in an Ar-33CO-7H2-7CO2-2H2O (vol.%) gas simulating a blast furnace operating condition. A relatively short reaction time, up to 100 h, was used to evaluate the initial stage of metal dusting of these alloys in the blast furnace gas condition. Severe metal dusting and coke deposition were observed at 550 °C, while no significant dusting but internal oxidation and carburization were observed at 650 °C. Higher Cr and Ni contents in the alloy lowered kinetics of metal dusting at 550 °C and of carburization at both temperatures. Austenitic alloys were more susceptible to metal dusting and coke deposition than ferritic alloys with the same Cr content at 550 °C. At 650 °C, however, ferritic alloys experienced higher extents of carburization and oxidation than austenitic alloys with the same Cr concentration. The effects of alloy composition and reaction temperature on metal dusting in this simulated blast furnace operating condition were discussed.

Atomistic characterization of multi nano-crystal formation process in Fe–Cr–Ni alloy during directional solidification: Perspective to the additive manufacturing

The directional solidification phenomenon has been observed in conventional castings and state-of-the-art manufacturing processes like additive manufacturing of steel. Precise control of temperature gradient during directional solidification in the additive manufactured components is essential to get growth and evolution of various crystalline structures, which enhance the properties. In this study, we have used molecular dynamics simulation to investigate the directional solidification of Fe–Cr–Ni steel under a wide range of temperature gradients. It is observed that multiple crystal morphology such as single crystal, nano-grains, multiple stacking faults, twins etc. Form during directional solidification depending on the temperature gradient. Evolution of various crystalline structures characterized by adaptive common neighbour analysis, surface area, volume and corresponding dimensionless aspect ratio. The current investigation adds to the pedagogical understanding of the effects of thermal gradients on the evolution characteristics of crystal morphology evolved during modern additive manufacturing processes.

Elastic modelling of lattice distortions in concentrated random alloys

Lattice distortions, i.e. small atomic displacements away from the average lattice, are linked to a number of functional and mechanical properties of concentrated metallic alloys, particularly their yield strength. Here we develop an elastic model of lattice distortions where every atom is modeled as an Eshelby inclusion in a homogeneous elastic matrix. Local environment effects are included by considering fluctuating anisotropic eigenstrain tensors associated to the inclusions. The model is tested on several concentrated alloys, face-centered cubic (FCC) AlMg and FeNiCr alloys, as well as a fictitious body-centered cubic (BCC) binary alloy to study systematically and independently the effects of a size and an elastic modulus mismatch between the constituents. The elastic model predicts lattice distortions well when the size and elastic modulus mismatches are typically less than 5% and 25%, respectively. Interestingly, we find that when the size mismatch is small, as in FeNiCr alloys, the lattice distortion is dominated by the fluctuations of the dilatational eigenstrains rather than their average value as often assumed in elastic models of concentrated alloys. Moreover, models usually assume homogeneous elastic constants, while the limit obtained here of 25% is often exceeded in concentrated alloys, particularly with a BCC structure.

Effects of inclusion type and inclusion radius on deformation characteristic and failure mechanism inside monocrystalline NiFeCr alloy

The effect of different inclusion types, inclusion radius, and strain rates (STRs) on the mechanical property, deformation behaviors, energy absorption, and failure mechanisms of NiFeCr alloy is investigated through a molecular dynamic simulation of a tensile process. The tensile strength, strain energy, and dislocation densities of the sample without and with inclusion all increase as increasing STRs. However, the tensile strength, strain energy, and dislocation densities of the sample without inclusion are all larger than those of the sample with inclusion. Moreover, Young’s modulus (E) of the none-inclusion sample is a little smaller than that of the Fe-inclusion sample while larger than that of the Ni-inclusion and Cr-inclusion samples. The results also show that the effect of inclusion radius is complex, which depends on the type of material that makes up the inclusion. E values decrease as increasing inclusion radius for all inclusion types. The phase transformations from FCC to HCP structure and the dislocation length for the none-inclusion sample are much larger than that of the inclusion samples. Besides, the nuclear deformed appears at the contact area between the inclusion and the NiFeCr workpiece and then widely develops as increasing strain. The Stair-rod and Shockley partial dislocations consider a dominant proportion for all samples.

Control mechanism of gadolinium-rich precipitates in new nuclear shielding FeCrNi alloys

A series of different Ni content FeCrNi alloys incorporated with Gd was designed and fabricated. The gadolinium-rich precipitates in all alloys were identified through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The types of precipitates transformed from M3Gd to M5Gd (M = Fe, Ni, Cr) intermetallic compound when the Ni content reached 30 wt.%. With increasing Ni content, the melting temperature of both the M3Gd and M5Gd phases improved. The melting temperature of M5Gd was more than 1200 °C, which was higher than the M3Gd precipitate, and this made alloys have narrow solidification temperature range. The structural stability of the gadolinium-rich precipitate and the interfacial strength calculated by density functional theory is discussed. These fabricated alloys with more than 30 wt.% Ni content also gave excellent shielding properties and deserve further investigation.

Directly monitoring the shift in corrosion mechanisms of a model FeCrNi alloy driven by electric potential

Stainless steels are used in a myriad of engineering applications, including construction, automobiles, and nuclear reactors. Developing accurate, predictive mechanistic models for corrosion and electrochemical corrosion kinetics of stainless steels has been a topic of research studies over many decades. Herein, we quantified the aqueous corrosion kinetics of a model austenitic Fe–18Cr–14Ni (wt%) alloy in the presence and absence of applied potential using systematic in situ electrochemical atomic force microscopy (EC-AFM) and transmission electron microscopy (TEM). Without an applied bias, vertical dissolution of corrosion pits is controlled by the surface kinetics/diffusion hybrid mechanism, whereas lateral dissolution is diffusion controlled. When an electric bias is applied, the increase in corrosion rate is dominated by the nucleation of new pits. These insights gained by the in situ EC-AFM will allow applications of this method for a quantitative understanding of corrosion of a wider class of materials.

Integrated effect of aging and heavy ion radiation on FeNiCrAl duplex alloy for accident-tolerant fuel cladding

Alumina-forming duplex FeNiCrAl alloy with superior mechanical properties and high-temperature oxidation resistance has been regarded as an accident-tolerant fuel cladding material. This work investigated the effect of aging and the radiation resistance of FeNiCrAl duplex alloy after up to 2000 hours thermal aging and 3.5 MeV Fe13+ ion radiation. The ferrite phase containing B2 phase shows much fewer radiation defects and lower radiation hardening rate than conventional FeCrAl alloy. The coherent B2 phase precipitate is critical in hindering dislocation and inhibiting the formation of radiation induced defects which is proved via experiment and molecular dynamics simulation. Besides, the Al depletion of B2 phase and nano-sized precipitation are characterized by using Time-of-Flight Secondary Ion Mass Spectrometry and Atom Probe Tomography. These findings effectively illuminate microstructure evolution of FeNiCrAl duplex alloy after long-term aging and radiation and lead to new insight for designing advanced accident-tolerant fuel material.

Effect of Temperature on the Stress-Strain Response of the Fe–Cr–Ni Alloy

Effect of Temperature on the Stress-Strain Response of the Fe–Cr–Ni Alloy

Dislocation nucleation mechanisms during nanoindentation of concentrated FeNiCr alloys: unveiling the effects of Cr through molecular simulations

Fe-based alloys with high chromium and nickel concentrations are very attractive for efficient energy production in extreme operating conditions. We perform molecular dynamics (MD) simulations of nanoindentation on fcc FeNiCr multicomponent materials. Equiatomic FeNi, Fe55Ni19Cr26, and Fe74Ni8Cr18 are tested by using established interatomic potentials and similar conditions, for the elucidation of key dislocation nucleation mechanisms and interactions. Generally, we find that the presence of Cr in these alloys reduces the mobility of prismatic dislocation loops, and increases their area, regardless of crystallographic orientation. Dislocation nucleation and evolution is tracked during mechanical testing as a function of nanoindentation strain and Kocks–Mecking continuum modeling displays good agreement with MD findings. Furthermore, the analysis of geometrically necessary dislocations (GNDs) is consistent with the Ma–Clarke’s model at depths lower than 1.5 nm. The presence of Cr leads to a decrease of the GND density with respect to Cr-less FeNi samples, thus we find that Cr is critically responsible of increasing these alloys’ hardness. Post-indentation impression maps indicate that Ni–Fe–Cr compositions display strain localization and hardening due to high Cr concentration.