Fe-based Alloys Research Articles

Effect of transverse magnetic field annealing on the magnetic properties and microstructure of FeSiBNbCuP nanocrystalline alloys

Improving the high-frequency magnetic properties of Fe-based nanocrystalline alloys with high-saturation magnetic induction (Bs) has received extensive attention recently. The magnetic properties, microstructure, and magnetic domain structure of Fe76Si12B8Nb2.2Cu0.8P1 ribbons after normal isothermal annealing (NA) and transverse magnetic field annealing (TFA) were investigated. It was found that NA and in situ crystallization TFA (TFA1) have little effects on the Bs and coercivity (Hc) of the ribbons but they significantly affect the magnetic permeability (μ) and optimal annealing window. In contrast, TFA after nanocrystallization (TFA2) enables the ribbons to attain a higher μ in a wide frequency range and a wider annealing temperature range than NA and TFA1. The TFA2 ribbons exhibit a high Bs of 1.45 T, low Hc of 0.8 A/m, and high μ under 1 A/m of 24,000 and 16,600 at 1 and 100 kHz, respectively. The factors causing the improved soft magnetic properties were revealed in terms of magnetic anisotropy and magnetization processes.

Quantitative analysis of retained austenite in Nb added Fe-based alloy

The use of Pipelines for long-distance transportation of crude oil, natural gas and similar applications is increasing and has pivotal importance in recent times. High specific strength plays a crucial role in improving transport efficiency through increased pressure and improved laying efficiency through reduced diameter and weight of line pipes. TRIP-based high-strength and high-ductility alloys comprise a mixture of ferrite, bainite, and retained austenite that provide excellent mechanical properties such as dimensional stability, fatigue strength, and impact toughness. This study performs microstructure analysis using both Nital etching and LePera etching methods. At the time of Nital etching, it is difficult to distinctly observe second phase. However, using LePera etching conditions it is possible to distinctly measure the M/A phase and ferrite matrix. The fraction measurement was done using OM and SEM images which give similar results for the average volume fraction of the phases. Although it is possible to distinguish the M/A phase from the SEM image of the sample subjected to LePera etching. However, using Nital etching is nearly impossible. Nital etching is good at specific phase analysis than LePera etching when using SEM images.

Evaluation of fracture properties of annealed Fe–Si–B–Cr amorphous alloys using micro-tensile tests and blanking machinability

In this study, the change in the strength of B-rich Fe-based amorphous alloy was investigated as a function of its microstructure controlled by the annealing at temperatures from 713 to 873 K. The strength was measured by using a micro-tensile test in a focused ion beam apparatus, and its machinability was tested by a blanking test. It was found that the static strength and machinability of the alloy varied drastically depending on its microtexture. In the micro-tensile test, the as-received sample exhibited ductile fracture with a tensile strength of about 1200 MPa, concurring with the bulk material. During the annealing up to 773 K, fine Fe3B crystals stared to precipitate sparsely in the matrix, and α-Fe crystals grew around Fe3B the crystals. Due to this microstructural change, the tensile strength dropped down to about 300 MPa, the fracture mode changed from ductile to brittle, and the toughness of the alloy decreased significantly. However, when the annealing temperature exceeded 773 K, the microtexture changed to clear polycrystalline, and thus, large plastic deformation reappeared, and the tensile strength returned to about 900 MPa. The blanking test revealed that the annealing reduced the blanking resistance significantly, in particular, in the sample annealed at 763 K. High-quality machining traces without burrs and shear droops were obtained from this sample. From the viewpoint of machinability, it was concluded that the microstructure with the fine precipitates dispersed in the amorphous matrix was most appropriate for this amorphous alloy.

A Review of the Preparation, Machining Performance, and Application of Fe-Based Amorphous Alloys

Amorphous alloy is an emerging metal material, and its unique atomic arrangement brings it the excellent properties of high strength and high hardness, and, therefore, have attracted extensive attention in the fields of electronic information and cutting-edge products. Their applications involve machining and forming, make the machining performance of amorphous alloys being a research hotspot. However, the present research on amorphous alloys and their machining performance is widely focused, especially for Fe-based amorphous alloys, and there lacks a systematic review. Therefore, in the present research, based on the properties of amorphous alloys and Fe-based amorphous alloys, the fundamental reason and improvement method of the difficult-to-machine properties of Fe-based amorphous alloys are reviewed and analyzed. Firstly, the properties of amorphous alloys are summarized, and it is found that crystallization and high temperature in machining are the main reasons for difficult-to-machine properties. Then, the unique properties, preparation and application of Fe-based amorphous alloys are reviewed. The review found that the machining of Fe-based amorphous alloys is also deteriorated by extremely high hardness and chemical tool wear. Tool-assisted machining, low-temperature lubrication assisted machining, and magnetic field-assisted machining can effectively improve the machining performance of Fe-based amorphous alloys. The combination of assisted machining methods is the development trend in machining Fe-based amorphous alloys, and even amorphous alloys in the future. The present research provides a systematic summary for the machining of Fe-based amorphous alloys, which would serve as a reference for relevant research.

A Comparison of the Oxidation and Nitridation Properties of Selected Chromia- and Alumina-Forming Alloys at 800 °C

Three FeCrAl alloys and two chromia-formers (a stainless steel, and a Ni-base alloy) have been exposed in four environments (dry air, air + 20% H2O, 20% H2 + 20% H2O + Ar and 95% N2 + 5% H2) for 168 h at 800 °C. The corroded samples were investigated by SEM/EDS, XRD and gravimetry, and the formation of CrO2(OH)2(g) was measured as a function of time using a denuder technique. The Fe-base alloy formed a Cr-rich protective oxide scale in dry air and wet air but suffered break-away oxidation in 20% H2 + 20% H2O + Ar. In contrast, the Ni-base alloy suffered extensive NiO formation and internal oxidation in dry air and wet air but formed a protective chromia scale in 20% H2 + 20% H2O. All three FeCrAl alloys formed protective alumina scales in dry air, wet air and 20% H2 + 20% H2O + Ar. The FeCrAl alloy Kanthal APMT was severely nitrided in the 95% N2 + 5% H2 environment due to defects in the oxide scale associated with RE-rich inclusions which allowed nitrogen to enter the alloy. In contrast, the two Cr-lean FeCrAl alloys Kanthal EF101 and Kanthal EF100 did not suffer nitridation at all.

Sintering, microstructure and properties of absorbable Fe–Mn-xCu alloys

One issue with Fe-based biodegradable alloys is their relatively slow degradation rate inside the body. In addition, the ferromagnetic nature of Fe intensely limits its application in magnetic resonance imaging (MRI). In this work, the role of copper addition on powder processing, microstructure, and performance of the Fe–35Mn alloy is described. Fe–35Mn based samples containing 0 to 10 wt% Cu were fabricated by ball milling, uniaxial cold pressing, and sintering. The alloys were characterized for their compressive strength, corrosion behavior, and magnetic properties. Results of XRD analysis showed that copper addition promoted ferrite to austenite phase transformation during sintering. Microstructures of the alloys containing up to 3 wt% Cu were composed of a simple solid solution and large pores. However, when Cu content increased to 6 wt%, a free pure Cu phase appeared in the microstructure, resulting in enhanced densification by forming a liquid phase during sintering. Consequently, the compressive yield strength continuously increased with increasing Cu content and reached the maximum value of 203 MPa in the FeMn–10Cu alloy. The corrosion rate also increased with increasing Cu content up to 6 wt%. An average corrosion rate of 0.27 mm/year was found for the FeMn–6Cu alloy, which was more than five times the rate of the base Fe–Mn alloy. The magnetic susceptibility of the alloys decreased with increasing Cu content, indicating a higher MRI compatibility.

Effect of phosphorus segregation on carbides and creep damage of Ni–Fe-based GH984G alloy

The effect of phosphorus segregation on carbides and creep damage of Ni–Fe based GH984G alloy, for the application of advanced ultra-super critical (A-USC) power plant, were investigated under the creep condition of 750 °C and 200 MPa. The results indicate that the primary precipitates of GH984G alloy are MC, M23C6 and γ′ after standard heat treatment. P-doping has no effect on the grain size, γ′ size and morphology. Nevertheless, P atoms segregate at the grain boundaries and around the MC carbides, resulting in a change in the morphology of M23C6 carbides at grain boundary from film-like to granular and a decrease in the density and area percentage of MC carbides. The creep behavior of GH984G alloy at 750 °C/200 MPa changes significantly after P doping and the creep properties (creep life and elongation) are optimized with the increasing P content. The damage feature is microcrack at grain boundaries for P-free alloy, while the creep cavities in P-doped alloy. The fracture mode changes from intergranular fracture to transgranular fracture with the increasing P doping for GH984G alloy after creep at 750 °C/200 MPa. The optimizing of creep properties and transformation of fracture mode of GH984G alloys after P doping are mainly attributed to increase of grain boundary cohesion and the change of carbides caused by the P segregation behaviors during creep process.

Crystallization Toughening of Fe-Based Amorphous Alloys Under Strain–Heat Coupling Effect

Crystallization Toughening of Fe-Based Amorphous Alloys Under Strain–Heat Coupling Effect

Study on fabrication technology and corrosion resistance of Fe-based amorphous alloy coatings by high-speed laser cladding

In this paper, the AME201 Fe-based amorphous alloy coating was prepared by ultra-high speed laser cladding on the surface of 27SiMn alloy steel. The effects of technological parameters on the surface morphology, micro-structure and dilution rate of coating. Corrosion resistance and weight loss of matrix, AME201Fe coating, 316L coating and Fe901 coating were studied by salt spray corrosion test. The results show that the thickness of AME201Fe coating is mostly affected by powder feeding, laser power and scanning speed have a huge impact on the width of coating, and the dilution rate increased from 0.13% to 29% with the change of laser power, nearly several hundreds of times. The results of salt spray test show that the AME201Fe coating has the minimum weight loss value at each stage compared with the matrix, 316L coating and Fe901 coating, which can play a good role in surface protection because of less internal defects and no grain boundary dislocations.

Phase and Structural Transformations in the Fe-Based Alloys under the Combined High-Energy Treatment

Applying the x-ray, metallographic, and microdurometric methods, the phase composition and structural–stress state of the Fe-based alloys under the impact of electrospark treatment in combination with laser processing are studied and analysed. As shown, the structural–phase state of electrospark coating on the steel substrate is determined by several factors. They are the dissociation of WC carbide on the surface of alloying electrode on the W2C and W components followed by their erosion, an interaction of erosion products with elements of the interelectrode medium (C, N, O), an interdiffusion of the coating elements and a steel substrate, and the ascending diffusion of C from the substrate near-surface layers. As revealed, the heterophase coating and near-surface layers of substrate possess a complex structural–stress state. As shown, the residual stresses in different phase components have been formed through different regularities: the tensile stresses in the TiC-based compound, while the compressed stresses in the W2C, W, and Feα. The selective effect of laser heating of the coating on the stresses of different signs is revealed.

Mg-, Zn-, and Fe-Based Alloys With Antibacterial Properties as Orthopedic Implant Materials.

Implant-associated infection (IAI) is one of the major challenges in orthopedic surgery. The development of implants with inherent antibacterial properties is an effective strategy to resolve this issue. In recent years, biodegradable alloy materials have received considerable attention because of their superior comprehensive performance in the field of orthopedic implants. Studies on biodegradable alloy orthopedic implants with antibacterial properties have gradually increased. This review summarizes the recent advances in biodegradable magnesium- (Mg-), iron- (Fe-), and zinc- (Zn-) based alloys with antibacterial properties as orthopedic implant materials. The antibacterial mechanisms of these alloy materials are also outlined, thus providing more basis and insights on the design and application of biodegradable alloys with antibacterial properties as orthopedic implants.

The Role of Grain Boundaries in the Corrosion Process of Fe Surface: Insights from ReaxFF Molecular Dynamic Simulations

Intergranular corrosion is the most common corrosion phenomenon in Fe-based alloys. To better understand the mechanism of intergranular corrosion, the influence of grain boundaries on Fe-H2O interfacial corrosion was studied using molecular dynamics simulation based on a new Fe-H2O reaction force field potential. It is found that the corrosion rate at the polycrystalline grain boundary is significantly faster than that of twin crystals and single crystals. By the analysis of stress, it can be found that the stress at the polycrystalline grain boundary and the sigma5 twin grain boundary decreases sharply during the corrosion process. We believe that the extreme stress released at the grain boundary will promote the dissolution of Fe atoms. The formation of vacancies on the Fe matrix surface will accelerate the diffusion of oxygen atoms. This leads to the occurrence of intergranular corrosion.

Manipulating shock waves with metallurgy

Existing methods for disrupting shock waves employ low-density materials and mesostructures, which occupy significant space, are difficult to fabricate, and are often destroyed after loading. In this work we produce a gradient metamaterial with near-uniform density capable of disrupting shock waves fifty-fold in time. We utilize metastable volumetric contraction at the atomic-scale during α↔ϵ phase transformation in Fe-based alloys to disrupt shock waves. Gradient Fe-xMn alloys are fabricated and shock compressed to pressures approaching 13 GPa, with shock rise times increasing from ∼20 ns in pure Fe to ∼1000 ns in the Fe-xMn laminate. Shock-recovered microstructures indicate that the phases reversibly transform. Two-dimensional simulations, validated against planar experiments, predict geometries that can effectively focus or dissipate shock waves. To our knowledge, this work is the first to demonstrate manipulation of shock waves via alloying of phase-transforming metamaterials.

Ultrasonic-Assisted Shearing Characteristics of Fe-Based Amorphous Alloy Strips

Ultrasonic-Assisted Shearing Characteristics of Fe-Based Amorphous Alloy Strips

The Benefit of the Glassy State of Reinforcing Particles for the Densification of Aluminum Matrix Composites

In metallic glass-reinforced metal matrix composites, the glassy phase can serve a dual purpose: (i) it can behave as soft binder and porosity remover during consolidation; and (ii) it can act as the hard reinforcing phase after densification. The present work aimed to demonstrate the benefit of the glassy reinforcing particles for the densification of aluminum matrix composites. The consolidation behavior of Al–50 vol.% Fe-based alloy mixtures prepared using a glassy Fe66Cr10Nb5B19 alloy powder (Tg = 521 °C, Tx = 573 °C) or a crystalline Fe62Cr10Nb12B16 alloy powder was studied under spark plasma sintering (SPS) and hot pressing (HP) conditions. The powders were consolidated by heating above the glass transition temperature of the glassy alloy (up to 540 °C in SPS and 570 °C in HP). When the coarse aluminum powder was used, the reinforcing particles formed chains within the microstructure. In composites formed from the fine Al powder, the particles of the Fe-based alloy were separated from each other by the metallic matrix, and the tendency to form agglomerates was reduced. The glassy state of the alloy was shown to be beneficial for densification, as the metallic glass acted as a soft binder. The densification enhancement effect was more pronounced in the case of reinforcing particles forming chains. The hardness of the Al–50 vol.% glassy Fe66Cr10Nb5B19 composites obtained by SPS was twice the hardness of the unreinforced sintered aluminum (110 HV1 versus 45 HV1).

3D and 4D Printing of Complex Structures of FeMnSi‐Based Shape Memory Alloy Using Laser Powder Bed Fusion (Adv. Mater. Interfaces 13/2022)

3D Printed Fe-Shape Memory Alloys In article number 2200171, Dohyung Kim, Irene Ferretto, Christian Leinenbach and Wookjin Lee demonstrate 3D and 4D printing of Fe-based shape memory alloy using laser powder bed fusion technique for the first time. Integrating the material-inherent functionalities into complex 3D structures allows for new functionalities of structures including shape morphing, metal-material behavior, and extraordinary specific strength with shape memory behavior.

Research Progress of Fe-Based Superelastic Alloys

In recent years, superelastic alloys have become a current research hotspot due to the large recoverable deformation, which far exceeds the elastic recovery. This will create more possibilities in practical applications. At present, superelastic alloys are widely used in the fields of machinery, aerospace, transmission, medicine, etc., and become smart materials with great potential. Among superelastic alloys, Fe-based superelastic alloys are widely used due to the advantages of low cost, easy processing, good plasticity and toughness, and wide applicable temperature range. The research progress of Fe-based superelastic alloys are reviewed in this paper. The mechanism of thermoelastic martensitic transformation and its relation to superelasticity are summarized. The effects of the precipitate, grain size, grain orientation, and texture on the superelasticity of Fe-based superelastic alloys are discussed in detail. It is expected to provide a guide on the development and understanding of Fe-based superelastic alloys. The future development of Fe-based superelastic alloys are prospected.

Effect of Copper Addition on the Phase Composition and Microstructure Evolution of Fe-Based Amorphous Alloy Coatings Prepared by Laser Cladding

Laser clad coating’s susceptibility to cracking is extremely high due to the brittleness of the material itself and the enormous residual stress caused by rapid heating and cooling. In order to relieve the residual stress, a series of Fe-based amorphous-Cu composite coatings were fabricated on 20 steel using laser processing. The effects of copper addition on the phase composition and microstructure evolution of the coatings were then investigated. The as-prepared coatings, which are mainly composed of Fe-based amorphous, Cu, and (Fe, Cr)23 (C, B)6 have a network microstructure. A large amount of spherical-shaped copper metal is present in the coating and is evenly dispersed within the amorphous matrix. The copper in the coating has little effect on the crystallisation of Fe-based amorphous alloys due to the negligible solubility of solid copper and the Fe-based amorphous alloy. The coating average hardness reduces considerably and shows a significant difference, improving the coating stress distribution.

Direct Observation of Cu Clusters and Dislocation Loops by Cs-Corrected STEM in Fe-0.6wt%Cu Alloy Irradiated in BR2

The neutron irradiation of Fe-based fusion and fission reactor materials leads to an increase in ductile-to-brittle transition temperature with a decrease in upper shelf energy. It is well known that Cu content has a strong influence on the embrittlement phenomenon, as Cu-rich clusters (CRPs) are thought to be directly responsible for embrittlement. In contrast, mechanical property studies for steels with different Cu levels exhibit dominant matrix defects in the embrittlement of both low-Cu steels and high-Cu steels at high fluences. To determine the effects of dislocation loops and CRPs on radiation hardening in those steels, neutron irradiation was conducted on Fe-0.6wt%Cu alloy. The neutron irradiation was performed in BR2 at 290 °C up to a dose of 4.1 × 1024 n/m2. After irradiation, the microstructure was observed and analyzed by spherical aberration-corrected transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) combined with X-ray energy-dispersive spectroscopy, using a JEOL ARM200FC. This technique enabled simultaneous observation of ~10 nm CRPs and dislocation loops. Additional high-voltage electron irradiation was performed at room temperature, and the dislocation loops were identified as interstitial-type dislocation loops. Radiation-induced hardening due to neutron irradiation was estimated by measuring the size and density of the dislocation loops and the CRPs. These results suggest that simultaneous observation of dislocation loops and CRPs using the Cs-corrected STEM with EDS analysis is essential for the study of radiation-induced hardening in Fe-based alloys.

Wear Resistance of Fe-Based Amorphous Powder Deposited Coatings in Air, Water, and SBF Solution: Effect of Layer Number

Amorphous alloys have high strength and high hardness, showing their potential applications as tribological materials. In order to improve the wear resistance of 316L stainless steel (SS), Fe-based amorphous powder was deposited on 316L SS by laser cladding. Since the microstructure of the laser clad coating was sensitive to the dilution between coating and substrate, multilayer Fe-based metallic coatings were fabricated layer by layer. When the laser cladding layer number increased, the microstructure evolved from a complete crystalline phase to a mixed structure with amorphous phase and dendrite. Meanwhile, the amorphous content increased and the average microhardness was enhanced. Accordingly, the wear resistance was improved generally under all the sliding conditions, including in air, distilled water, and simulated body fluid (SBF) solution. For the lubricant effect of liquid, the coefficients of friction in distilled water and SBF solution are relatively lower than that in air. Compared with 316L SS, the volume loss rate of nine-layer coating decreased by two orders of magnitude in air and about 5.5 times in SBF solution. Except for one-layer coating, the predominant wear mechanism of the laser clad coatings in air is abrasive wear accompanied by oxidative wear. The wear mechanism in SBF solution is dominated by abrasive wear and corrosive wear. The superior hardness and good corrosion resistance are responsible for the outstanding wear resistance improvement. Therefore, the laser clad coating with Fe-based amorphous alloy has a potential application in the surface strengthening of mechanical parts or metallic implants.