Fe Ni Cr Research Articles

Atomistic analysis of the mechanisms underlying irradiation-hardening in Fe–Ni–Cr alloys

This work presents a comprehensive examination of the physical mechanisms driving hardening in irradiated face-centered cubic FeNiCr alloys. The evolution of irradiation-induced defects during shear deformation is modeled by atomistic simulations through overlapping cascade simulations, where the nucleation and evolution of dislocation loops is validated by transmission electron microscopy images obtained from irradiated FeNiCr alloys using tandem accelerator. The effect of different shear rates on the microstructure of irradiated materials with a specific focus on the changes in the density of voids and dislocation loops induced by irradiation was analyzed. Additionally, the fundamental interaction processes between single irradiation-induced defects contributing to irradiation hardening, such as voids and dislocation loops in the alloy are explained. The analysis at atomic level indicates that both the dislocation loops and the voids exhibit strengthening effects. Furthermore, the nanometric voids are much stronger obstacles than dislocation loops of comparable size. The mechanism of cutting the voids leads to an increase of voids density and thus contributes to an increase in irradiation hardening. The mechanism of collapse of small voids into dislocation loops leads to decrease of voids density and at the same time increase of loops density. The coupling effect between the density of voids and dislocation loops is determined. Finally, the novel, physical mechanisms-based model of irradiation hardening and dislocation-radiation defect reaction kinetics are developed, which consider the mechanisms of void cutting, void shrink and void collapse to dislocation loop.

Enhancing strength-ductility combination of Fe–Ni–Cr–Al–Ti high-entropy alloys via co-precipitation of sigma and L21 phases

The sigma phase is a well-known harmful phase in transition metal alloys, leading to severe embrittlement due to its inherent brittleness. However, in this work, we develop a new strategy to obtain enhanced strength-ductility combination via the synergistic effects of interlocking co-precipitation of the sigma and L21 phases in Fe40Ni30Cr20Al5Ti5 (at. %) high-entropy alloy (HEA). This HEA exhibits a good strength-ductility combination after aging treatment (800 °C for 4h), with a yield strength (YS) of about 920 MPa and an ultimate tensile strength (UTS) of about 1300 MPa while maintaining a total elongation (TE) of 24 %. It is attributed to the interlocking co-precipitation of the sigma and L21 phases with equal volume fractions into the face-centered cubic (FCC) matrix through thermomechanical treatment. During the tensile deformation, the softer L21 phase coordinates the deformation around the sigma phase, suppresses the local stress concentration, and achieves a stable high work hardening capability, as well as stacking faults (SFs) networks and density Lomer-Cottrell (L-C) locks, contributes to the excellent strain hardening capacity and thus obtains the enhanced strength-ductility combination in the HEA. This study will provide a new strategy to obtain enhanced strength-ductility combination for alloys containing brittle and hard topologically close-packed (TCP) phases, such as the sigma phases.

The alloyed cementite (Fe–Ni–Cr)3C: Local environment, atomic magnetic moments, and magnetization from DFT calculation

The alloying element added to carbon steel to enhance its properties also penetrates Fe3C cementite particles, altering their properties and influencing the steel product through them. This is why the impact of alloying elements on cementite has been extensively studied. Ni and Cr exhibit opposing behavior in cementite, so cementite doped with Ni and Cr is investigated using DFT calculations. The data obtained for total energy, lattice, magnetization, local magnetic moments at metal atoms, and their nearest environment are compared to experimental magnetic data for Ni and Cr-alloyed cementite. The relationship between Fe atom magnetic moments and their nearest environment is discussed in comparison between Cr and Ni doping. Decrease in magnetization with Ni and Cr content is attributed to 1) replacement of a larger Fe magnetic moment (mFe = 1.9–2.0 μB) with a smaller or even negative moment (mNi = 0.2–0.5 μB, mCr = −0.3 to −1.0 μB); 2) a decrease in the average Fe moment with the number of Cr atoms in the nearest environment; and 3) a strong dependence of the Curie temperature on Cr content in Cr-doped cementite.

First-principles and cluster expansion study of the effect of magnetism on short-range order in Fe–Ni–Cr austenitic stainless steels

Short-range order (SRO), the regular and predictable arrangement of atoms over short distances, alters the mechanical properties of technologically relevant structural materials such as medium/high entropy alloys and austenitic stainless steels. In this study, we present a generalized spin cluster expansion (CE) model and show that magnetism is a primary factor influencing the level of SRO present in austenitic Fe–Ni–Cr alloys. The spin CE consists of a chemical cluster expansion combined with an Ising model for Fe–Ni–Cr austenitic alloys. It explicitly accounts for local magnetic exchange interactions, thereby capturing the effects of finite temperature magnetism on SRO. Model parameters are obtained by fitting to a first-principles data set comprising both chemically and magnetically diverse face-centered cubic configurations. The magnitude of the magnetic exchange interactions are found to be comparable to the chemical interactions. Compared to a conventional implicit magnetism CE built from only magnetic ground state configurations, the spin CE shows improved performance on several experimental benchmarks over a broad spectrum of compositions, particularly at higher temperatures due to the explicit treatment of magnetic disorder. We find that SRO is strongly influenced by alloy Cr content, since Cr atoms prefer to align antiferromagnetically with nearest neighbors but become magnetically frustrated with increasing Cr concentration. Using the spin CE, we predict that increasing the Cr concentration in typical austenitic stainless steels promotes the formation of SRO and increases order–disorder transition temperatures. This study underscores the significance of considering magnetic interactions explicitly when exploring the thermodynamic properties of complex transition metal alloys. It also highlights guidelines for customizing SRO through adjustments of alloy composition.

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.

Effect of aging temperature on microstructure and mechanical properties of Fe–Ni–Cr–Al high entropy alloy

Investigating the strength–plasticity synergy of metal structural materials is a crucial scientific challenge. This study focuses on preparing high-entropy alloys (HEAs) comprising Fe–Ni–Cr–Al, which exhibit a heterostructural coexistence of several phases through cold rolling and aging (CRA). Above 600 °C CRA, the average grain size of the HEA was refined from 260 to 1.64 μm, and numerous annealing twins were formed. Concurrently, two forms of irregularly ordered body-centred cubic (B2) phases and nanoscale ordered face-centred cubic (L12) phases were precipitated. Large B2 particles precipitated along the grain boundary, whereas small B2 and L12 particles precipitated within the grains. The average sizes of the B2 and L12 particles were 510 and 2.21 nm, respectively. The fine grain and precipitation strengthening enhanced the HEA yield strength (from 254 to 710 MPa). The difference in plastic strain between the matrix and precipitate causes long-range back-stress strengthening and heterodeformation-induced hardening, enhancing the strain-hardening ability and maintaining the superior plasticity of the HEA. This study provides an effective approach for obtaining metal structural materials with strength–plasticity synergy.

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.

Corrosion Behaviour of Fe-Based and Ni-Based Alloys in Wet CO2 Gas with and without Chloride Deposits at 750 °C

Corrosion behaviours of Fe–25Cr, Fe–25Cr–2Mn–1Si, Fe–25Cr–20Ni, 310SS, Ni–25Cr, and Ni–25Cr–2Mn–1Si (all in wt%) with and without NaCl–KCl deposits in Ar–60%CO2–20%H2O gas at 750 °C were studied. Without salt deposits, Fe–25Cr performed protectively, while Fe–25Cr–20Ni and Ni–25Cr underwent breakaway oxidation with multilayered scales formed. Adding alloy elements Si + Mn increased the corrosion resistance of all alloys by forming additional Mn-rich oxides and silica. Surface deposits of NaCl–KCl accelerated corrosion, forming porous Fe-rich oxide nodules for Fe–25Cr and thick, porous scales and internal oxidation zones for all other alloys. The protective effect of Si + Mn alloying disappeared in the presence of chlorides. Limited intergranular carbides were observed for all alloys in the gas-only condition. The extent of carburisation increased with the presence of chloride deposits for all Fe-based alloys, but remained unchanged for Ni-based alloys. Corrosion of these alloys at 750 °C is compared with that at 650 °C. The effect of chlorides in volatilising metals at 750 °C is discussed.

Novel Fe‐Based Amorphous Brazing Foils in the Quinary System Fe–Ni–Cr–Si–B

Amorphous brazing foils are increasingly used on a wide variety of component geometries because of their flexibility and the resulting ease of application. Due to the recent rapid rise in Ni prices, there is an enormous need for research into the substitution of nickel with iron within conventionally used nickel‐based amorphous brazing foils. To avoid time‐consuming series of experiments, newly developed thermodynamic databases will be used to predict alloy compositions with a high glass forming ability. Foils should be produced with the melt‐spin process and characterized with differential scanning calorimetry and secondary electron microscopy. Novel iron‐based brazing foils with different compositions are successfully produced in the alloying system iron–nickel–chromium–silicon–boron. The characterization of these foils indicates the presence of a partly amorphous or nanocrystalline structure. The novel iron‐based brazing foils are characterized by a simple and cost‐efficient alloying concept. Furthermore, newly developed thermodynamic databases in the iron–nickel–chromium–silicon–boron system are validated by the successful production of these foils. The prediction of further iron‐based amorphous foils with the aid of thermodynamic calculations can thus be made possible.

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.

Thermochemical Study of the Formation of Silicides, Borides, and Carbides in an Fe–Ni–Cr–Cu–Si–B–C Alloy

Thermochemical Study of the Formation of Silicides, Borides, and Carbides in an Fe–Ni–Cr–Cu–Si–B–C Alloy

Effect of austenitizing temperature and cooling rate on Ms temperature of Fe–Ni–Cr cast iron

The effect of Ms temperature variation in Fe–Ni–Cr cast iron has been investigated in this paper. The heating and cooling processes were carefully compared and analysed through in-situ observation. The results showed that the size of austenite grains remained relatively constant throughout the austenitizing process. Moreover, higher austenitizing temperatures were found to facilitate the transfer of carbon from graphite to austenite, which hindered the martensite transformation. The M3C and M23C6 carbide generated during heating and cooling diminished the concentration of carbon and alloying elements in the austenite and enhanced the Ms temperature. The acceleration of cooling rate could impede the precipitation of carbide and result in more significant lattice distortion of austenite, leading to a notable reduction in Ms temperature and an increment in residual austenite content. The augmentation in austenitizing temperature and cooling rate amplified the non-chemical driving force, culminating in a more arduous martensitic transformation.

Microstructure evolution and fracture mechanism of a Fe–Ni–Cr superalloy during various strain rates tensile deformation at elevated temperatures

Microstructure evolution and fracture mechanism of a Fe–Ni–Cr superalloy during various strain rates tensile deformation at elevated temperatures

Molecular Dynamics Study on Hugoniot State and Mie-Grüneisen Equation of State of 316 Stainless Steel for Hydrogen Storage Tank.

To promote the popularization and development of hydrogen energy, a micro-simulation approach was developed to determine the Mie-Grüneisen EOS of 316 stainless steel for a hydrogen storage tank in the Hugoniot state. Based on the combination of the multi-scale shock technique (MSST) and molecular dynamics (MD) simulations, a series of shock waves at the velocity of 6-11 km/s were applied to the single-crystal (SC) and polycrystalline (PC) 316 stainless steel model, and the Hugoniot data were obtained. The accuracy of the EAM potential for Fe-Ni-Cr was verified. Furthermore, Hugoniot curve, cold curve, Grüneisen coefficient (γ), and the Mie-Grüneisen EOS were discussed. In the internal pressure energy-specific volume (P-E-V) three-dimensional surfaces, the Mie-Grüneisen EOSs show concave characteristics. The maximum error of the calculation results of SC and PC is about 10%. The results for the calculation deviations of each physical quantity of the SC and PC 316 stainless steel indicate that the grain effect of 316 stainless steel is weak under intense dynamic loads, and the impact of the grains in the cold state increases with the increase in the volume compression ratio.

Effect of Mo addition on the microstructural evolution and mechanical properties of Fe–Ni–Cr–Mn–Al–Ti high entropy alloys

High-strength alloys are in urgent demand for engineering applications. Inducing multiple strengthening phases in a ductile matrix by microalloying is an effective alloy-strengthening strategy, especially the simultaneous formation of geometrically close-packed (GCP) phases and topologically close-packed (TCP) precipitation in high entropy alloys (HEAs). In this study, the microstructural evolution and mechanical properties of a series of (FeNi)67Cr15Mn10-xAl4Ti4Mox HEAs with x values of 1, 2, 3, 4, and 5 were analyzed in detail, with the substitution of Mn by Mo. This substitution does not change the L12 phase forming elements (Ni, Al and Ti) in the alloy, and enhance the σ phase precipitation, which meantime does not modify the oxidation resistance in thermal mechanical treatment. After aging at a temperature of 1023 K for 5 h, the matrix of the HEAs still maintains a face-cubic-centered structure. However, as Mn is replaced by Mo, hard σ precipitates are introduced into the matrix and the grains are significantly refined when x < 5. Therefore, the yield strength monotonically increases with increasing x. However, the formation of the hard σ precipitates also hinders the sustainability of the work hardening process, and thereby decreases the plasticity of the HEAs. Hence, the elongation at break monotonically decreases with increasing x. However, the high density of σ phase precipitates obtained at x = 5 prematurely terminates the work hardening process. Therefore, the highest ultimate tensile stress is obtained at x = 4, rather than x = 5. This also changes the fracture morphology from a coarse grain morphology for x < 5 to a typical brittle fracture at x = 5. Accordingly, (FeNi)67Cr15Mn6Al4Ti4Mo4 obtains the optimal mechanical properties overall.

Molecular dynamics simulation of corrosion and its inhibition: comparison of structural stability of Fe/FeNi/FeNiCr/FeNiCrTi steels under high-temperature liquid lead

The liquid lead used in fast nuclear reactor has been known to be able to cause a significant damage to the steels. Therefore, finding new materials with high corrosion resistance is the goal of much research current days. Likewise, developing a way to prevent corrosion is also the goal of designers of nuclear reactors. In the present study, we studied materials: Fe, FeNi, FeNiCr, and FeNiCrTi (a type of SS 316L austenite steel), comparing their structural stability when interacted with molten liquid lead at 750 °C. The performance of each steel is compared under high-temperature molten lead coolant, checking the structure's stability to see the material resistance to corrosion attack of liquid lead. The corrosion can also be seen from the data of iron diffusion coefficient. The larger of the iron diffusion coefficient can be associated with larger corrosion because there is a high solubility of iron atoms from the steel surface to the molten lead. The popular way to prevent more corrosion is by injecting oxygen into the lead coolant. This current work uses the molecular dynamics method to simulate the corrosion and inhibition phenomena. The research aims to compare the performance of Fe, FeNi, FeNiCr, and FeNiCrTi under liquid lead at a temperature of 750. The diffusion coefficient of iron of material will be calculated to describe quantitatively the corrosion level of those structural materials and the corrosion inhibition by oxygen injection. The study has produced important results that adding Ni, Cr, Ti into a pure iron crystal to build alloy steel will make the material stronger, structurally compact, and more resistant to corrosion. For specific composition of steels, from weaker to stronger that resist from corrosion attack, it is possible to make ordering: Fe&lt;&lt;FeNi&lt;FeNiCr&lt;FeNiCrTi. The composition of FeNiCrTi steel in this work is Fe(75)Ni(10.57)Cr(14.05)Ti(0.40). The high corrosion of FeNiCrTi in the liquid lead is effectively reduced by injecting 0.0112 wt % oxygen into lead coolant as a limit value for maximum corrosion inhibition

Heterogeneous grain size and enhanced hardness by precipitation of the BCC particles in medium entropy Fe–Ni–Cr alloys

We report the chemical-composition-dependent precipitation of Cr-rich BCC particles and their role in the hardening of Fe–Cr–Ni medium entropy alloys (MEAs). Three alloys with different chemical compositions: 33Fe–32Cr–35Ni MEA (33Fe), 40Fe–30Cr–30Ni MEA (40Fe), and 45Fe–30Cr–25Ni MEA (45Fe) (at%), were investigated. After annealing at 800 and 950 °C, all three alloys had a heterogeneous grain size distribution, except for 40Fe annealed at 950 °C. The samples annealed at 800 °C showed a more heterogeneous grain size distribution, smaller average grain size, and lower degree of recrystallization than the samples annealed at 950 °C. This difference is ascribed mainly to the contents and precipitation kinetics of Cr-rich BCC particles at the two temperatures. The hardness decreased with the increase in annealing temperature for all the samples. The 33Fe sample exhibited higher hardness than 40Fe and 45Fe because of the joint effect of grain boundary strengthening and precipitation strengthening by the Cr-rich BCC particles. Different peak-load-dependent hardness behaviors were observed in 33Fe-A800 with relatively coarse BCC particles and 40Fe-A800 with fine BCC particles. The fine particles led to higher local hardness, whereas coarse particles resulted in higher microhardness owing to the hetero-deformation-induced strengthening effect. These results provide new insights into the strength optimization of medium- and high-entropy alloys through the dispersion of coarse Cr-rich BCC particles.

Investigation of ultrafine WC–Co–Fe–Ni–Cr3C2 cemented carbide microstructure and properties based on phase diagram thermodynamics

Abstract In this work, different Fe/Ni ratios with constant Co content were prepared to explore microstructure and properties of ultrafine WC-10 wt.%(Co–Fe–Ni)-Cr3C2 cemented carbides. The increase in Fe content in binder has difficulty in controlling carbon content. Therefore, the carbon window was determined by phase diagram to prepare carbon-balanced cemented carbides. The increase in Fe/Ni ratio in the binder deteriorates the uniformity of the binder phase distribution and refines the WC and binder phase grains by affecting the solubility of WC in binder and the wettability of the binder. Grain size, microstructural irregularities and solid solution strengthening of binder phase affect the mechanical properties of cemented carbides. The relative density of cemented carbide with Fe/Ni = 30:70 in the binder is 99.8 % and the transverse fracture strength is 2449 MPa maximum, but the fracture toughness is slightly low. Because of the passivation characteristics of Ni, the alloy with Fe/Ni = 0:100 in the binder has better resistance to corrosion resistance.

Size effects in stress propagation and dynamics of dislocations: Fe–Ni–Cr steel

Movement of line dislocations in fcc steel 310S is found to depend on the size of nanometer sized structures, based on modeling within molecular dynamics (MD). The effect is attributed to time (and size) dependencies of pressure propagation into the medium interior. The observation is crucial in interpreting any MD studies of pressure effects since these are governed by time-dependent internal virial stresses. In particular, velocity of dislocations scales better with value of local internal shear component of virial stress S xy than with external shear pressure applied. Dynamics of stress penetration is described well within the model of damped harmonic oscillator, where characteristic oscillation frequency depends on number of crystallographic layers in direction along the wave propagation while the speed of stress propagation is the speed of sound. The minimal stress required for dislocation movement (Peierls stress) is determined to be 0.75 GPa. Pressure and temperature effects on dislocation movement are systematically investigated.

Surface texture characterization for thin-wall NASA HR-1 Fe–Ni–Cr alloy using laser powder directed energy deposition (LP-DED)

Additive Manufacturing (AM) offers new design and manufacturing opportunities of thin-wall microchannel heat exchangers for aerospace and industrial applications. Laser Powder Directed Energy Deposition (LP-DED) is an AM process providing large scale manufacturing of thin-wall microchannel heat exchangers. Successful industrialization of the LP-DED process requires critical quantification and understanding of the metallurgical, geometric, and process limitations. Specifically, understanding the as-built surface texture, inclusive of roughness and waviness, is significant due to its effects on the friction factor and pressure drop within a heat exchanger. This experimental study completed a design of experiments (DOE) to determine the critical build parameters that impact surface texture for enclosed thin-wall samples. This study summarizes the characterization work of the LP-DED process for 1 mm enclosed walls with an Fe–Ni–Cr (NASA HR-1) alloy. The LP-DED parameters including laser power, powder feedrate, travel speed, layer height, and rotary atomized powder feedstock were modified in the experiment. An evaluation of the DOE samples and resulting surface texture is provided along with conclusions from these experiments. Results indicate that 3D areal and 2D profile (directional) surface texture is estimated by 2x the powder diameter that becomes captured or partially melted on the trailing edge of the melt pool. The fine powder showed a higher sensitivity to parameter changes but resulted in a higher density material and 23% reduction in roughness. Surface texture was also shown to vary between closed channel shapes (internal) due to ricochets, recirculation, and higher volume of powder available to bond compared to external (outer) surfaces. The understanding of the LP-DED process as-built surface texture is essential to fluid flow applications such as heat exchanges and can modify performance for enhanced heat transfer or can be a detriment to pressure drop.