Iron-chromium Alloys Research Articles

Pourbaix diagrams for iron-chromium alloys in lithium bromide absorption machines

The influence of lithium bromide concentration on the Pourbaix diagrams for iron-chromium alloys is evaluated in this work, which allows for predicting the corrosion to stainless steels exposed to the aggressive operating conditions of lithium bromide absorption machines (concentrations ranging from: 400–992 g/L). The novelty of this work is found in the development of Pourbaix diagrams for the Fe-Cr-Br–-H2O quaternary system in aqueous solutions with a high concentration of lithium bromide, a topic which has not yet been studied. Results show that the corrosion region at acid pH corresponding to the aqueous species FeBr2(aq), FeBr3(aq), Cr+2, CrOH+2, Cr+3 or CrBr+2 shifts to higher pHs with increasing lithium bromide concentration, which decreases the immunity region of iron and chromium and decreases the passivation region of the solid species FeCr2O4, Fe2O3 and Cr2O3.

Magnetic Hardening of Heavily Helium-Ion-Irradiated Iron–Chromium Alloys

This study reports on the magnetic hardening phenomenon of heavily helium ion-irradiated iron–chromium alloys. The alloys are important structural materials in next-generation nuclear reactors. In some cases, problems may arise when the magnetic properties of the materials change due to neutron irradiation. Therefore, it is necessary to understand the effects of irradiation on magnetism. Helium irradiation was conducted as a simulated irradiation, and the effect of cavity formation on magnetic properties was thoroughly investigated. High-quality single-crystal Fe-x%Cr (x = 0, 10, 20) films, with a thickness of 180–200 nm, were fabricated through ultra-high vacuum evaporation. Subsequently, irradiation of 19 dpa with 30 keV He+ ions was conducted at room temperature. X-ray diffraction measurements and electron microscopy observations confirmed significant lattice expansion and the formation of high-density cavities after irradiation. The magnetization curve of pure iron remained unchanged, while magnetic hardening was noticed in iron–chromium alloys. This phenomenon is believed to be due to the combined effect of cavity formation and changes in the atomic arrangement of chromium.

РАЗРАБОТКА СПЕЧЕННОГО ФРИКЦИОННОГО МАТЕРИАЛА ДЛЯ ГИДРОТРАНСФОРМАТОРА ГМП САМОСВАЛОВ БЕЛАЗ

The torque converter is designed to transmit mechanical energy from the engine through a circulating fluid flow and automatically steplessly changes, within certain limits, the angular speed and transmitted torque depending on the load on the dump truck wheels. The torque converter makes it possible to achieve low speeds of the dump truck with increased traction on the drive wheels, ensures stable engine operation when the load changes, and also helps reduce dynamic loads in the dump truck transmission. The paper presents the results of a study of the effect of iron-chromium alloy powder ПХ30 (PKh30) on increasing the performance properties of sintered friction material for use in the torque converter locking clutch of a hydromechanical transmission. This is achieved due to the high physical and mechanical properties of PKh30, and the Cr23C6 layer formed during the sintering process with a thickness of up to 6 μm. It is established that the introduction of 10–40 vol.% of PKh30 powder helps to increase the friction coefficient from 0.042 to 0.075, with the maximum content being 28 %. Based on the data obtained, the composition of the composite friction material ФМ-15 (FM-15) was developed and patented. The manufactured friction discs, installed and operated in the hydromechanical transmission torque converter of the BELAZ-7555E mining dump truck with a load capacity of 60 tons, showed high performance properties. The developed composition of the friction material is also used in the friction clutches of the loading and hauling machine MoAZ-40751 with a load capacity of 16 tons and the loading and transport mine machine MoAZ-75851 with a load capacity of 50 tons with an electronic-hydraulic automatic control system. The study of tribological properties was carried out on a friction machine ИМ 58 (IM 58). The morphology of the friction surface was studied on a scanning electron microscope MIRA (Czech Republic) with an INCA 350 micro-X-ray spectral attachment from Oxford Instruments (United Kingdom). Phase composition was determined on an Ultima IV X-ray diffractometer of Rigaku Company (Japan) in CuKα radiation at an X-ray tube voltage of 40 kV, anode current of 40 mA.

Исследование режимов термосиловой обработки напыленных модифицированных слоев

The paper presents the findings of a study investigating the properties of sprayed coatings with subsequent electrothermally treated within the context of the Ministry of Internal Affairs of the Republic of Kazakhstan grant project AR19680421. This study considers the peculiarities of electric current flow through the sprayed coating or pre-formed powder layer. The properties of 40X13 steel coatings obtained by hypersonic metallization followed by electrothermosilic treatment are investigated. A method for obtaining a wear-resistant coating is proposed, including the formation of a jet of sprayed particles of two metal wires melted in an electric arc, their deposition as a layer on a pre-prepared surface of the part and subsequent electrothermosilic treatment of the layer. It is proposed to choose martensitic steel as the material of one wire, nickel–chromium or iron-chromium alloy with high electrical resistivity as the material of the other, and the diameter of the wire made of this alloy should be determined depending on the diameter of the steel wire.

Towards enhancing ODS composites in laser powder bed fusion: Investigating the incorporation of laser-generated zirconia nanoparticles in a model iron–chromium alloy

Oxide dispersion-strengthened (ODS) steel is a sought-after composite material known for its high demand in high-temperature and corrosive environments. Achieving the desired ODS steel properties requires specific conditions for the size and nanoparticles (NP) distribution in the printed part. Laser ablation in liquid (LAL) enables precise NP size adjustment. At the same time, the dynamic melt pool solidification in the Laser Powder Bed Fusion (PBF-LB/M) process complements this by creating favorable conditions for successful ODS processing. In this study, ZrO2 NP with a small and narrow particle size distribution (d50 = 3.8 nm; d90 = 10 nm) is produced by LAL. Dielectrophoretic deposition achieves the homogeneous, deformation-free coating of the binary Fe20Cr (wt.-%) matrix powder with NP. PBF-LB/M printed parts out of the oxide-additivated powder exhibit a crack-free structure and a density of up to 98%. Expectedly, the metal matrix grain sizes and room temperature microhardness (~ 220 HV) are not affected by NP addition. NP tracing by 2D simulation indicates a homogeneous NP distribution and less than 10% NP to be agglomerated in the solidified part. Thus, a promising perspective for a complete laser-based process chain for generating and processing ODS alloys is outlined.Graphical abstractTable of Contents

Oxidation Behavior and Outward Diffusion of Al Along Oxide Grain Boundaries of FeCrAl Alloys Overdoped with Zr and Hf

AbstractThe formation of the α-Al2O3 scale on reactive element (RE)-doped FeCrAl alloys is commonly believed to be primarily caused by inward oxygen transport along grain boundaries. However, this study suggests that metal ion outward diffusion also plays a role in the development of the oxide scales and their microstructural characteristics. The study examines the oxidation behavior and grain boundary outward diffusion of iron-chromium alloys containing ~ 10 at% aluminum and ~ 22 at% chromium, doped with an over-critical concentration of REs, i.e., Zr and Hf. All samples were investigated after thermal exposure at 1100 °C by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). As a result of the overdoping, a considerable increase in oxide growth, an increase in the depth of internal oxidation, and RE-oxide formation near and at oxide grain boundaries (GBs) were observed as a consequence of increased inward and outward diffusion. The effect of overdoping manifests itself differently depending on the RE type and amount due to different solubility, ionic size, and electronic structure of alumina. The sample with Zr retained the adhesion of alumina to the alloy after the first and second thermal exposure, while Hf overdoping resulted in severe spallation after the second thermal exposure.

Composite super-capacitor/Na-ion battery with self-healing Fe–Cr alloy electrodes

In this study, we synthesize a novel self-healing supercapacitor (SC) by combining a thermally and alkali-activated carbon interface with a unique chromium–iron alloy. Detailed device electrochemistry is presented, complemented by characterizations through XRD, SEM, and EDS analyses of electrode surfaces. We introduce rapid cyclic voltammetric measurements to illuminate electrical performance and charge storage of fabricated SCs. SEM measurements demonstrate heightened cycling efficiency, indicating reduced electrolyte degradation and dormant sodium metal formation. XRD measurements support SCs’ self-enhancement, evidenced by sodium metal formation and improved crystalline properties on electrode surfaces. SEM micrographs reveal distinct nanostructures—nanoneedles, nanoflowers, carbon nanotubes, and graphene—formed during charge–discharge cycles. EDS confirms reversible Na metal formation, while increased Cr peaks, acting as corrosion inhibitors, highlight self-healing, extending SC lifespan. Attaining a capacitance of around 30 mF and capacity of 55.6 mWh/kg, the material offers at least 1500 μF/g. Initial results showcase a composite SC/Na-ion battery with favorable and scalable SC characteristics.

Dynamics of Nucleation in Solids: A Self-Consistent Phase Field Approach.

We derive a phase field method for computing rigorously the nucleation rate and the incubation time from the sole knowledge of the free energy of the system in the metastable regime. Our theoretical results are assessed against experimental data relative to demixing of an iron-chromium alloy. Our work clarifies the notions of nucleation rate and incubation time extensively used in classical nucleation theory (CNT) processes in solids. Our work thus emerges as an alternative to CNT but of more general applicability, and enables us to model the nucleation process across the whole range of condition encountered in first order phase transitions, an aspect in which CNT fails.

Low-Potential Zone at the Interface of Precipitate and Austenite Affecting Intergranular Corrosion Sensitivity in UNS N08028 Nickel–Iron–Chromium Alloy

The precipitates and the intergranular corrosion behavior of a UNS N08028 nickel–iron–chromium alloy sensitized at different temperatures were studied by employing transmission electron microscopy, Kelvin probe force microscopy and other methods. It was found that sigma precipitates appeared at the grain boundaries of the alloy being sensitized. There was a Cr-depleted zone and a low-potential zone around these precipitates. The potential difference between the sigma precipitates and the low-potential zone was 102 mV, and this increased with the growth of the sigma precipitates. At this potential difference, the migration of the vacancies in the passive film accelerated significantly, and then the protectiveness of the passive film decreased. The intergranular corrosion mechanism of the steel has also be discussed.

Effects of Aluminum and Molybdenum on the Phase Stability of Iron-Chromium Alloys: A First-Principles Study

Effects of Aluminum and Molybdenum on the Phase Stability of Iron-Chromium Alloys: A First-Principles Study

Electrolytic coating of iron-chromium alloy of sulphate-chloride electrolyte in machine parts recovery process modelling

Introduction. The technological process of restoring a part should provide more than 80% of the resource and no more than 50% of the cost of a new part. The wear resistance of the applied coating determines the resource of the restored part operating under waterjet and boundary friction. The microhardness of an iron-based electrolytic coating is one of the key indicators of wear resistance. The study of the results of statistical processing and the factors most affecting the increase in the microhardness of the iron-based coating will make it possible to recommend and optimize the deposition conditions for obtaining the most wear-resistant coatings.Materials and methods. The studies on equipment that let to obtain the necessary data with the required accuracy were carried out. The mathematical processing using modern statistical data processing tools that excluded possible errors, let to obtain the dependence of factors with the necessary accuracy was carried out.Results. During the study of the developed sulfate-chloride electrolyte for the deposition of an iron–chromium coating, it became necessary to determine the effect of deposition conditions – ‘factors’ (temperature, acidity of the electrolyte, cathode current density) on the microhardness of the coating – ‘response’. It was found that the combination of the factors ‘temperature’ and ‘cathode current density’ in the coded values of 1.5. 2.0 and -2 are the most significant. The deposition conditions in order to obtain a coating with maximum microhardness are optimized.Discussion and conclusions. As a result of the conducted studies for the effect of the deposition conditions of the Fe-Cr alloy from the sulfate-chloride electrolyte on the microhardness of the coating, it was found that in order to obtain high-quality coatings of the iron-chromium alloy with high microhardness, it is necessary to strictly comply with the requirements of the deposition conditions and acidity to a greater extent. As the current density and temperature of the electrolyte, compared with the acidity of the electrolyte, iron baths are installed and regulated by equipment.

High-temperature Corrosion of ~ 30 Pct Porous FeCr Stainless Steels in Air: Long-Term Evaluation Up to Breakaway

In this work, a long-term (up to 6000 hours) corrosion evaluation of three porous (~ 30 pct of initial porosity) ferritic iron-chromium alloys with different Cr contents (20, 22, and 27 wt pct of Cr) was carried out at 600 °C, 700 °C, 800 °C, and 900 °C in air. Mass gain measurements and SEM analyses revealed that at temperatures above 600 °C, all alloys exhibit breakaway corrosion, whereas at 600 °C, none of the alloys were heavily oxidized even after 6000 hours. Based on the results, the diffusion character of the corrosion of porous chromia-forming alloys was identified. The microstructure changes at high temperatures in porous alloys containing 22 wt pct of Cr were determined in detail by transmission electron microscopy. The proposed prediction model indicated that the lifetimes of the Fe20Cr and Fe22Cr alloys were determined as 1250 hours (± 535 hours) and 1460 hours (± 640 hours), respectively. It is in agreement with the long-term oxidation experiment. For the Fe27Cr alloy, the deviation between predicted and observed lifetimes occurs. The proposed model allows for qualitative estimation of the porous alloys’ lifetime with experimentally validated accuracy.

Combustion Characteristics and Performance Evaluation of Modified Mesoscale Annular Combustor

ABSTRACT The combustion characteristics and performance of a cylindrical stagnation flow-type mesoscale annular combustor were evaluated. The combustor comprised inner and outer porous tubes made of stainless steel and nickel – chromium–iron alloy, respectively. A rich C3H8–air mixture and air were supplied to the inner and outer tubes, respectively. The cylindrical flame was formed around the inner tube; consequently, a petal-type flame was formed downstream of the cylindrical flame. Experiments were conducted by maintaining a constant flow rate q i of the rich C3H8–air mixture in the inner tube while varying the equivalence ratio φ i of the mixture and the airflow rate q o of the outer tube. To investigate the combustion characteristics, the temperature was measured inside and at the outlet of the combustion chamber. The burned gas compositions, O2, CO, and NO, were analyzed. The heat loss rate η hl and the exergy loss rate η ex,loss were evaluated from the obtained temperature data. The minimum values of η hl and η ex,loss were 0.06 at φ i = 1.5, φ all = 0.3, and 0.44 at φ i = 5.0, φ all = 0.8, respectively. The values of η hl and η ex,loss verified that the combustor offers high performance.

Influence of Chromium Atoms on the Shear-Coupled Motion of [110] Symmetric Tilt Grain Boundary in α-Iron: Atomic Simulation

Shear-coupled grain boundary motion (SCGBM) is an important mechanism of plastic deformation, especially in the cases of ultrafine-grained or nanocrystalline materials at low temperatures. Much research work has been focused on the geometric rules of coupling, the grain boundary migration mechanisms, or the temperature effect of SCGBM, but the effect of the alloy atoms is seldom involved. In this work, molecular dynamics (MD) simulations were carried out to examine the SCGBM of the Σ17[110](223) and Σ9[110](221) grain boundaries (GBs) in iron-chromium alloys containing from 1 at.% to 9 at.% Cr. A constant shear velocity corresponding to 10 m/s parallel to the boundary plane was applied to the models. Our simulation results indicate that the critical stress of GB migration reduces due to the addition of Cr atoms for the Σ17(223) GB. As for the Σ9(221) GB, sliding occurs simultaneously with coupling in the shear process when the atomic amount of Cr reaches 3%. This phenomenon was also observed in the Σ9(221) GB in pure Fe when the temperature was elevated to 300 K, which was studied in our previous simulation work. The existence of new structural units was demonstrated to be responsible for the sliding of the grain boundary.

Effect of Lanthanum Oxide Addition on Microstructure and Wear Performance of Iron-Chromium Alloy Manufactured by Laser Direct Deposition Additive Manufacturing.

Additive Manufacturing (AM) has become increasingly common, and its use in various industries is increasing. However, the microstructure, friction and wear performance of metals made by AM, such as the inexpensive and relatively good-performing iron-chromium alloys, require further investigation. Generally, adding rare earth elements can effectively improve the performance of AM alloys, such as tensile strength, wear resistance, corrosion resistance, creep resistance, etc. This work aims to study the variation of microstructure, friction and wear properties of laser additive manufacturing processed iron-chromium alloys after adding different mass fractions of La2O3. The observations obtained by scanning electron microscopy showed that, with the addition of La2O3, the microstructure of AM alloy becomes more uniform and the grains are significantly refined. It is found by friction test that the running-in period is significantly shortened after the addition of La2O3. The coefficient of friction is reduced to a minimum of 0.68. Compared with AM alloys without La2O3, the wear rate of AM alloys with La2O3 is significantly reduced, with a maximum reduction of 38%. Using an optical microscope to observe the surface morphology of the wear scar, it is found that, after adding rare earth oxide, the wear mechanisms changed from adhesive wear and abrasive wear to abrasive wear, with the spalling of hard particles at the same time.

Magnetization and microhardness of iron–chromium alloy films electrodeposited from an aqueous solution containing N, N-dimethylformamide

Iron-chromium (Fe–Cr) alloy films were electrochemically synthesized from an aqueous solution containing N,N-dimethylformamide (DMF). The chromium content of the alloy films increased up to ca. 32 at%, with an increase in the cathodic overpotential during the electrodeposition. Based on the XRD profiles and electron diffraction patterns, it was revealed that the electrodeposited Fe–Cr alloy films have an amorphous nanocrystalline structure. The crystal grain size of the alloys decreased due to an alloying effect of Cr atoms as well as an increase in the nucleation site density of the alloys that were electrodeposited, accompanying a significant overpotential from the stable complex ions. The saturation magnetization of the electrodeposited Fe–Cr alloy films decreased with an increase in the chromium content. On the contrary, the microhardness increased due to the synergistic contribution of solid solution strengthening and crystal grain refinement. The microhardness of the electrodeposited Fe–Cr alloy films reached up to 422.0 kgf/mm2 (HV0.05) and greatly exceeded that of the solidified Fe–Cr alloy ingots.

Comparative Analysis over Tribology Characterization of TiAlN and TiAlSiN PVD Coating on Plasma Nitride Alloy 20

The nickel–iron–chromium (alloy 20) is enriching by hybrid surface treatment through plasma nitride (PN) and physical vapor deposition (PVD) process. The plasma nitriding process takes 12 h at 500 °C. Potentiodynamic testing is used to characterize the corrosion performance of the treated material, followed by morphological analysis of the exposed surface; XRD, EDX, SEM, hardness, and tensile testing are used to investigate appropriate coating properties. Plasma nitride and hybrid PVD nickel–iron–chromium alloys exhibit perlite (γ + α′) phases and martensite (γ + α) phases, respectively. The martensite microstructure ensures superior tensile strength and hardness. The pin-on-disc tribometer test proposes to analyze friction and hard-faced behavior in the dry sliding position. The inclusion of Si improves the adherent oxide film, resulting in a low wear rate in TiAlSiN alloy 20. Due to the presence of the passive film, TiAlSiN alloy 20 exposes the most passive region to attain better corrosion resistance.Graphical Abstract

Hardness and Microstructure Homogeneity of Pure Copper and Iron-Chromium Alloy Processed by Severe Plastic Deformation

Hardness and microstructure homogeneity of pure copper and iron-chromium alloy processed by severe plastic deformation (SPD) were investigated in grain refinement. Equal channel angular pressing (ECAP) is one of the well-known techniques of the SPD technique due to their up-scale ability and other methods. SPD was applied to pure copper and iron-chromium alloy at comparable temperatures up to four passes. The microstructure and microhardness were observed and measured in the transverse plane for each billet. The homogeneity observation was carried out from the sub-surface until in the middle of the billet. The result showed that the deformed structure appeared adequately after the first pass and had a higher hardness level. The first pass showed a higher inhomogeneity factor than the fourth pass due to the homogeneity microstructure. The hardness also showed homogeneous value along the transverse plane, and it was concluded that ECAP could achieve complete homogeneity in grain refinement

Interatomic Fe–Cr potential for modeling kinetics on Fe surfaces

To enable accurate molecular dynamics simulations of iron–chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe–Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe–Cr, we extend our potential fitting database to include not only conventional bulk properties but also surface-segregation energies of Cr in bcc Fe. In terms of reproducing our DFT results for the bulk properties, the new potential is found to be superior to the previously developed Tersoff potential and competitive with the concentration-dependent and two-band embedded-atom-method potentials. For Cr segregation toward the (100) surface of an Fe–Cr alloy, only the new potential agrees with our DFT calculations in predicting preferential segregation of Cr to the topmost surface layer, instead of the second layer preferred by the other potentials. We expect this rectification to foster future research, e.g., on the mechanisms of corrosion resistance of stainless steels at the atomic level.

Microstructure and Strain Hardening Behaviour of Iron Chromium Alloy Subjected by Severe Plastic Deformation

Microstructure and strain hardening behaviour of iron-chromium alloy subjected to severe plastic deformation (SPD) have been investigated in grain refinement and deformation routes. Equal channel angular pressing (ECAP) was used in this SPD technique due to their un-change dimension billet. The purpose of this research is to investigate the structure and the strain hardening of iron chromium alloy subjected by ECAP process. The ECAP process was carried by routes A, Bc and C up to four passes at 423 K temperature. The strength of the material was measured by tensile testing with 3 mm gauge length, and the strain hardening behaviour was investigated based on the true stress-strain curve. The effect of the deformation route on microstructure and texture was observed by electron backscattered diffraction (EBSD) analysis at the normal, transverse and rolling direction. The result showed that route Bc showed the highest strength and ductility of the ECAP processed material compare to other routes due to their 90 degrees rotation of each ECAP passes number. The increased strength of materials was also associated with grain refinement and accumulation dislocation. It concluded that the ECAP process by route Bc could be used for further material treatment and application for industrial purposes.