Fe Cr Ni Alloys Research Articles

Bond Synergy Model for Bond Energies in Alloy Oxides

In this work we introduce a metal-oxide bond-energy model for alloy oxides based on pure-phase bond energies and bond synergy factors that describe the effect of alloying on the bond energy between cations and oxygen, an important quantity to understand the formation of alloy oxides and their composition. This model is parameterized for binary cation-alloy oxides using density-functional theory energies and is shown to be directly transferable to multi-component alloy oxides. We parameterized the model for alloy oxide energies with metal cations that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo, Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of pure-phase bond energies in oxides and the calculated bond energy values give sensible results compared to common experience, including the role of Cr as the passive-layer former in Fe–Ni–Cr alloys for corrosion applications. Additionally, the bond synergy factors give insights into the mutual strengthening and weakening effects of alloying on cation-oxygen bonds and can be related to enthalpy of mixing and charge neutrality constraints. We demonstrate how charge neutrality can be identified and achieved by the oxidation states that the different cations assume depending on alloy composition and the presence of defects.

Cobalt-element-free eutectic medium-entropy alloys with superior mechanical performance and processability

A new composition-design strategy was used to guide the development of Co-free eutectic high-entropy alloy. In the present work, we successfully realized the prediction of the eutectic point of CrFeNiNbx through the energy-dispersive spectrometer data of CoCrFeNiNbx. After that, we systematically investigated the effect of the Nb content on the phase-structure evolution and macro-mechanical properties of the equiatomic CrFeNi alloy. Experimental results show that the removal of Co reduces the eutectic point and decreases the solubility of the Nb element in the face-centered-cubic (FCC) phase. Compared with the Co-bearing eutectic, there are not obvious change of the morphology of the Co-free eutectic, while the interlaminar spacing and volume of the FCC phase increased, which resulting in a decrease in yield strength but a certain degree of improvement in compressive strain.

Exploring failure modes of alumina scales on FeCrAl and FeNiCrAl alloys in a nitriding environment

Two high-temperature FeCrAl and FeNiCrAl alloys were exposed in a strongly nitriding environment at 900 °C and the morphology of nitridation was studied. Quasi-in-situ experiments revealed that nitridation started at specific surface sites directly related to the alloy microstructure where the alumina scale was permeable to nitrogen. FeCrAl alloy grains with (112) orientation formed outward-growing alumina scales and were susceptible to nitridation. Outward-growing scales and substrate nitridation was also observed at chromium carbide precipitates in the FeNiCrAl alloy. Both alloys suffered nitridation at reactive element-rich (Y and Zr) inclusions larger than a certain critical size. The latter type of attack is caused by cracks and pores in the scale. The findings open new avenues of research for developing the next generation of high temperature alloys with superior properties.

Modelling and prediction of hardness in multi-component alloys: A combined machine learning, first principles and experimental study

In present study, the relations between hardness and elemental descriptors in the multi-component alloys (MACs) are particularly uncovered via machine learning (ML) and first-principles calculations. The RBF neural network is utilized to efficiently train a large database which allows an acceptable accuracy for identifying the overall role of elemental features for target properties. Detailed information from ML predictions indicates the critical element of Al and its significant advantages for the hardness in a model Al–Cr–Fe–Ni system. Investigations on elastic properties using first-principles calculations provide relations between physical quantities and match well with ML model. Furthermore, the Al1.2CrFeNi alloy was selected as an example, experimentally synthesized and properties-identified, to provide a strong validation in this case. Combined with some other reported alloys in this system, the prediction of the developed model can achieve above 90%. Further experimental analysis found that a dual phase microstructure presents in the Al1.2CrFeNi alloy, leading to a superior work hardening ability compared with the reported high performance alloys. This study offers reliable composition-properties features and encourages more researches using this integrated approach to guide for tuning novel MACs.

A simple model for nitrogen-induced lattice expansion of γ'N and γ N phases in Fe–Cr–Ni alloys with different chromium contents

ABSTRACT A recent publication on low-temperature nitriding of Fe–Cr–Ni alloys with various combinations of Cr and Ni contents showed experimentally the co-existence of γN and γ'N phases. An important result of the investigations was that with increasing Cr-content in the alloy, the lattice expansion induced by nitrogen dissolution in short-range ordered (SRO) γN is more pronounced than in the long-range ordered (LRO) γ'N phase. Eventually, for Cr contents beyond about 12 wt.%, the lattice expansions of the two co-existing phases become inseparable with X-ray diffraction investigation. The present contribution gives a simplified visualisation and prediction of the lattice expansion to explain this phenomenon. It is demonstrated that 25% of the N atoms trapped by Cr resides in LRO positions of γ'N-Me4N (Me = Fe,Cr,Ni).

Effect of Cooling Rate on the Precipitation Behavior of a Fe–Cr–Ni Alloy

Ferrite (δ) in two-phase austenite–ferrite Fe–Cr–Ni alloys decomposes into Mo- and Cr-rich phases like sigma (σ) and chi (χ), when aged in the temperature range of 873–1273 K (600–1000 °C). The precipitation of these phases for a particular Fe-Cr-Ni alloy has an adverse effect on its mechanical properties and corrosion resistance. In the present work, precipitation behavior of UNS S32205 duplex stainless steel (a Fe–Cr–Ni alloy) during controlled cooling and heating (isothermal aging) has been studied in the temperature range of 973–1073 K (700–800 °C). Scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and energy-dispersive spectrometer (EDS) attached to SEM were used to characterize the microstructures. The effect of precipitation of σ and χ phases on the micro-hardness was also studied. The precipitation sequence for 1023 K (750 °C), when cooled from 12,000 to 5 °C/min, was δ → carbides → χ → σ, while for 1073 K (800 °C), it was found to be δ → χ → σ. The Mo-enriched metastable χ phase nucleates at the initial stage of aging which then transforms to stable σ precipitates. The amount of σ and χ phases increased with temperature and aging time, but temperature was found to have a dominant role than the cooling rate due to higher diffusion of solute atoms at high temperatures. EBSD studies did not show any orientation relationship between parent δ ferrite and σ phase.

Oxidation resistance of Fe–Cr–Ni laser cladding layer under supercritical water

In this work, the laser cladding technology was applied to deposit Fe–Cr–Ni alloy powder on the surface of mild steel (AISI 1015) to improve the oxidation resistance of the materials under supercritical condition. During the oxidation of supercritical water, crystals in different regions were bonded, resulting in transformation from equiaxial crystal to columnar crystal. Meantime, the Cr and Mn elements diffused from coating to substrate. Cr2O3 and Fe2O3 were formed after the reaction between the Cr and Fe elements in the coating and supercritical water and oxygen. After supercritical water oxidation for 1000 h, the surface of the Fe–Cr–Ni laser cladding coating still had good compactness and could effectively inhibit the oxidation of supercritical water.

Growth mechanism of surface scales on Ni–Fe–Cr alloys at 960 °C in air

The oxidation mechanism of Ni–Fe–Cr alloys was studied at 960 °C in air. The results showed that an outward-growing (Ni,Fe)3O4/Fe2O3 layer and a Cr internal oxidation zone were initially formed on Ni–Fe–10Cr alloy. With increasing oxidation time, a continuous Cr2O3 inner layer was developed between internal oxidation zone and substrate, and subsequently the internal oxidation zone was further oxidized into (Ni,Fe,Cr)3O4 spinel layer. For the Ni–Fe–15Cr alloy, a thin Cr2O3 layer was firstly formed and broken down after 5 h. Then the development process of scale was similar to that on Ni–Fe–10Cr alloy.

Correction to: On the morphology of grain boundary discontinuous reactions and phase identification in an advanced Cr–Fe–Ni alloy

In the original article, Fig. 15 is incorrect. The correct version of the figure is presented below.

On the morphology of grain boundary discontinuous reactions and phase identification in an advanced Cr–Fe–Ni alloy

On the morphology of grain boundary discontinuous reactions and phase identification in an advanced Cr–Fe–Ni alloy

Cryo-quenched Fe–Ni–Cr alloy decorative steel single crystals II: Alloy phases, structure, hardness, tensile, tribological, magnetic and electronic properties

Abstract We have previously reported (Boatner et al., J. Alloys Compd. 691 (2017) 666–671) on the discovery, formation, processing, and application of a new decorative ternary steel. alloy and on its use in a wide range of practical applications including: custom and commercial knives, art objects, jewelry, electronics, and furniture. This decorative property results when polished single crystals of the 70 wt%Fe-15 wt%Ni-15 wt% Cr austenitic alloy are cryo-quenched into the martensitic phase resulting in the formation of a three-dimensional raised pattern of mixed austenitic/martensitic laths. These laths propagate across large dimensions of the material due to the absence of grain boundaries in the single crystal. The macroscopic optically reflective 3-D decorative pattern reproduces the structural symmetry inherent in the single-crystal orientation. This pattern results solely from the metallurgical phase properties of the ternary alloy and is completely distinct from the properties of Damascus steels or more modern so-called pattern-welded steels. Here we use X-ray diffraction, nanoindentation, hardness measurements/scratch testing, tribological measurements, and alloy resistivity and magnetization methods to obtain a more fundamental and comprehensive study of the effects of the austenitic/martensitic phase transition on the structural and physical properties of the 70 wt%Fe-15 wt%Ni-15 wt% Cr alloy. These results reveal new insight into irreversible phenomena that are associated with the inhibited phase transition on heating of the two-phase, mixed austenitic/martensitic structure that is formed subsequent to cryo-quenching the alloy crystal to 77 K.

The Effect of Ni Content on the Corrosion Resistance of Some Fe–Cr–Ni Alloys in Simulated Body Fluids in the Presence of H2O2 and Albumin

The stainless steel alloys are greatly utilized for human orthopaedic and implants. The electrochemical behaviour of the stainless steel of Fe–17Cr–xNi alloys (x = 8, 10, 14) has been studied in simulated body fluid containing H2O2 and albumin at 37 °C. The electrochemical behaviour of the Fe–17Cr–8Ni, Fe–17Cr–10Ni and Fe–17Cr–14Ni has been investigated using the potentiodynamic polarization and electrochemical impedance spectroscopy, EIS. The surface morphology of the three alloys was examined before and after immersion in the simulated body fluid containing H2O2 and albumin using scanning electron microscope. The elemental composition of the oxide layer formed on the surface of the alloys after immersion in the electrolyte was obtained using energy dispersive X-ray analysis, EDX, technique. The metals released into the electrolyte has been determined using atomic absorption spectrophotometry. The EIS and potentiodynamic polarization results demonstrate that the Fe–Cr–14Ni alloy attains highest polarization resistance and the smallest rate of corrosion than Fe–17Cr–8Ni and Fe–17Cr–10Ni alloys. Fe–17Cr–14Ni is slightly influenced by immersion in simulated body fluid containing H2O2 and albumin which is confirmed by SEM images and metal release via formation of protective passive film. The surface analysis has shown the participation of the different alloying elements in the passive film.

Density, excess volume, and structure of Fe-Cr-Ni melts.

The relationship between the excess volume and the structure of Fe-Cr-Ni melts is investigated using containerless levitation and in situ high-energy synchrotron x-ray diffraction techniques. The density of six hypoeutectic Fe-Cr-Ni alloys along the 72 wt. % Fe isopleth was measured in the stable and undercooled regions, and the excess volume was evaluated as a function of Cr concentration. It is found that the 72Fe-Cr-Ni alloys exhibit a positive sign of excess volume and the amount increases with increasing Cr concentration. Analysis of the structure factor and pair distribution function of the alloy family reveals that the short-range order in the melt becomes more pronounced with decreasing Cr concentration; this demonstrates a direct correlation between the excess volume and local liquid structure. A characteristic signature of the icosahedral structure is observed in the structure factor of the melts, and the potential origin of the positive excess volume of the 72Fe-Cr-Ni alloys is qualitatively discussed in relation to the icosahedral structure.

Stainless steel-like FeCrNi nanostructures via electrodeposition into AAO templates using a mixed-solvent Cr(III)-based electrolyte

Electrodeposition of stainless steel-like materials such as FeCrNi alloy into micro- and nanotemplates provides a sustainable framework for creating biomedical-oriented micro- and nanocomponents with outstanding characteristics. While Cr(III)-based electrodeposition represents a ‘green’ alternative to toxic Cr(VI), its use is limited by Cr(III) aqueous chemistry which leads to the incorporation of impurities and the hydrogen evolution reaction (HER). These factors are responsible for low deposition efficiencies, brittleness and porosity. The current work sought to investigate the use of ‘green’ Cr(III)-glycine electrolyte to improve FeCrNi electrodeposition from Cr(III) precursors. Mixed-solvent electrolyte containing ethylene glycol (EG) was employed to reduce HER aftereffects. FeCrNi mixed EG electrolytes were compared to their aqueous counterparts to observe differences in Cr(III)-glycine complexation, coatings' composition and current efficiency. The feasibility of this method for creating nanostructures was verified by template-assisted electrodeposition using anodic aluminium oxide (AAO) templates. This study established that mixed-solvent electrolytes are an effective strategy to improve Cr(III)-based plating of alloys into miniaturised moulds. For the first time, electrodeposited FeCrNi nanowires (NWs) and nanotubes (NTs) were achieved via the framework developed in this work. The possible mechanisms controlling the morphological variations in FeCrNi nanostructures were discussed in relation to the kinetic and growth models in single metal electroplating into nanotemplates.

Work hardening mechanism based on molecular dynamics simulation in cutting Ni–Fe–Cr series of Ni-based alloy

In order to study the micro-forming mechanism of work hardening in cutting Ni–Fe–Cr series of Ni-based alloy using Cubic Boron Nitride (CBN) tool, the cutting model was established by means of molecular dynamics simulation analysis method. The Morse potential function and other potential functions were calculated to characterize the interaction between atoms. Then, the influence of variation of cutting force, the dislocation density, dislocation pile-up, Lomer-Cottrell dislocation, and solute atoms on work hardening are deeply analyzed. The results show that the metal surface with plastic deformation initiates a variety of internal mechanisms to hinder dislocation movement as dislocation density increases, dislocation motion and interaction between dislocations intensifies. The mechanism of work hardening in Ni–Fe–Cr alloy is not only dislocation pile-up that is not easy to slip or cannot slip or dislocation tangle caused by dislocation intersection, but also a lot of Lomer-Cottrell dislocations. The solute elements that reduce stacking fault energy indirectly affect the generation of Lomer-Cottrell dislocations. In addition, solute atoms in nickel-based alloys can pin dislocations, hinder the movement of dislocations, and promote dislocation tangle in the workpiece. Various mechanisms interact and influence each other, which is a complex whole.

Microstructure and properties of Fe–Cr–Ni alloy coatings on T10 steel by laser cladding

In the present study, Fe–Cr–Ni alloy coatings were produced by laser cladding using the blending powder of Cr and Ni on the surface of T10 steel. The composition of phase and microstructure were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD). The microhardness and corrosion resistance were investigated. The Fe–Cr–Ni cladding coatings composed of austenites and a few eutectic ferrites. And the content of eutectic ferrite in the grain boundary decreased with the decreasing Cr/Ni ratio of the blending powder. The Creq/Nieq ratio and the ferrite number (FN) of the coatings confirm that the solidification process was the AF mode for the Fe–Cr–Ni cladding coatings. The average microhardness value of Fe–Cr–Ni coatings was about 380HV0.2 and the Cr/Ni ratio of the blending powder was not an obvious effect. The corrosion resistance of Fe–Cr–Ni alloy coatings which was significantly superior to T10 steel decreased with the decreasing Cr/Ni ratio of the blending powder. This research exhibits that the Fe–Cr–Ni coatings and laser cladding processing have a potential engineering application value on hypereutectoid carbon steel.

Electrical and magnetic properties of amorphous Fe22.5Co22.5Ni22.5Cr22.5Zr10 alloy

This report is focused on the investigation of electrical and magnetic properties of distorted bcc system. The inspiration for the selection of amorphous Fe22.5Co22.5Ni22.5Cr22.5Zr10 alloy with a distorted bcc structure is based on the theoretical band calculation. It is confirmed that the free electron density of state of disordered bcc FeNiCr alloy increases at Fermi surface.Amorphous Fe22.5Co22.5Ni22.5Cr22.5Zr10 alloy, hereafter denoted as a-FeCoNiCrZr, shows among all the metallic materials the weakest temperature dependence of the electrical resistivity, ρ0(T). The weak ρ0(T) has been interpreted in the context of different physical processes such as tunnelling of free electrons and electron phonon interactions.Magnetically, a-FeCoNiCrZr consists of independent soft ferromagnetic clusters with average cluster size of about 1840 atoms. The Curie temperature, TC, was verified using Landau’s theory of second-order phase transitions in low non-zero external fields. The reduced magnetization, M(T)/M(0), as a function of reduced temperature, T/TC, is explained in the framework of the exchange integral fluctuation theory. The exchange integral fluctuation is dominant only at low external fields. At Bex = 9 T, the exchange integral fluctuation has no noticeable effect on reduced magnetization. At Bex = 9 T, the precision of magnetic clusters around the Bex controls the behaviour of reduced magnetization as function of temperature.

Modeling of Radiation-Induced Segregation in Fe–Cr–Ni Alloys

In the model of radiation-induced segregation based on the first and second Fick laws and taking into account the inverse Kirkendall effect, concentration profiles of the components of the concentrated Fe‒Cr–Ni alloy and radiation point defects at various temperatures, dislocation densities, and dose gain rates were obtained. Calculation of concentration profiles was carried out from the moment of the beginning of irradiation to reaching the stationary mode. The sensitivity of the concentrations of the components of the alloy near the surface from the input parameters (migration energies of vacancies Cr, Ni, Fe, migration energy of interstitial atoms, etc.) is analyzed.

Magnetic Fe–Cr–Ni oxide alloy nano-belts prepared from the chemical decomposition of a stainless steel screw (a top-down approach): an efficient and cheap catalyst for multicomponent reactions

A new, cheap, and accessible method has been used for the preparation of nano-belts from the chemical decomposition (top-down approach) of a cheap stainless steel screw and found as an efficient magnetically recyclable nanocatalyst for the preparation of quinolines and 1,8-dioxo-octahydroxanthenes under mild reaction conditions. The nano-belts, Fe–Cr–Ni oxide alloy, was prepared in a two-step synthesis and characterized with various instrumental methods. Due to magnetic property of the screw (a ferritic-alloy), the resultant nano-belts is magnetic. Magnetic Fe–Cr–Ni alloy nano-belts were applied toward efficient preparation of quinolines and 1,8-dioxo-octahydroxanthenes under mild conditions. The catalyst could be readily recovered and recycled for several consecutive runs, while it suffers from a very low metal leaching and subsequently efficiency drop.

Creep resistance of Fe–Ni–Cr heat resistant alloys for reformer tube applications

Relations between microstructure, phase transformations and creep resistance of austenitic Fe–Ni–Cr alloys are investigated. As-cast alloys with different silicon contents and an ex-service tube are submitted to laboratory agings to trigger specific phase transformations, and subsequently creep-tested at 950°C under stresses of 24–48 MPa. As-cast microstructures contain interdendritic chromium-rich M7C3 carbides with niobium-rich MC carbides. After aging at 950°C, primary M7C3 carbides transform into chromium-rich M23C6 carbides, associated to a loss in creep strength. The G phase present in the ex-service alloy is reversed into MC carbides by a heat treatment at 1100°C, associated to a slight decrease in creep resistance. Besides, the addition of silicon is highly detrimental to creep strength. Results can be used for alloy design.