Fe-based Alloys Research Articles

Corrosion behaviour of HVOF developed Mo-based high entropy alloy coating and selected hard coatings for high temperature geothermal applications

The corrosion behavior of High Entropy Alloy (HEA), wear-resistant cermets, self-fluxing Ni alloy, and Fe-based amorphous alloy coatings were investigated in simulated alkaline high-temperature geothermal environments with/without H2S and CO2 gases for geothermal applications. Phase density of the corrosive fluid (liquid/vapor) influenced the corrosion behavior in the test environments. The NiCrSiBFe self-fluxing coating formed a continuous corrosion surface film while the FeCrMoWMnBCSi amorphous coating was prone to localized corrosion in the liquid phase. The cermet coatings had pores and cracks that led to localized penetration while the CoCrFeNiMo0.85 HEA showed the highest corrosion resistance in all test environments with no localized corrosion damage.

Fe-Mn-Al-Ni Shape Memory Alloy Additively Manufactured via Laser Powder Bed Fusion

Fe-Mn-Al-Ni is an Fe-based shape memory alloy (SMA) featuring higher stability and low temperature dependency of superelasticity stress over a wide range of temperatures. Additive manufacturing (AM) is a promising technique for fabricating Fe-SMA with enhanced properties, which can eliminate the limitations associated with conventional fabrication and allow for the manufacture of complicated shapes with only a single-step fabrication. The current work investigates the densification behavior and fabrication window of an Fe-Mn-Al-Ni SMA using laser powder bed fusion (LPBF). Experimental optimization was performed to identify the optimum processing window parameters in terms of laser power and scanning speed to fabricate Fe-Mn-Al-Ni SMA samples. Laser remelting was also employed to improve the characteristics of Fe-Mn-Al-Ni-fabricated samples. Characterization and testing techniques were carried out to assess the densification behavior of Fe-Mn-Al-Ni to study surface roughness, density, porosity, and hardness. The findings indicated that using a laser power range of 175–200 W combined with a scanning speed of 800 mm/s within the defined processing window parameters can minimize the defects with the material and lead to decreased surface roughness, lower porosity, and higher densification.

Role of Cr Element in Highly Dense Passivation of Fe-Based Amorphous Alloy.

The effect of the Cr element on the corrosion behavior of as-spun Fe72-xCrxB19.2Si4.8Nb4 ribbons with x = 0, 7.2, 21.6, and 36 in 3.5% NaCl solution were investigated in this work. The results show that the glass formability of the alloys can be increased as Cr content (cCr) is added up to 21.6 at.%. When cCr reaches 36 at.%, some nanocrystals appear in the as-spun ribbon. With increasing cCr content, the corrosion resistances of as-spun Fe-based ribbons are continually improved as well as their hardness properties; during the polarization test, their passive film shows an increase first and then a decrease, with the highest pitting potential as cCr = 7.2 at.%, which is confirmed by an XPS test. The dense passivation film, composed of Cr2O3 and [CrOx(OH)3-2x, nH2O], can reduce the number of corrosion pits on the sample surface due to chloride corrosion and possibly be deteriorated by the overdosed CrFeB phase. This work can help us to design and prepare the highly corrosion-resistant Fe-based alloys.

Superhydrophobic Fe-based amorphous alloy coatings with excellent anti-fouling and anti-corrosion properties by picosecond laser texturing

Producing superhydrophobic surfaces on the amorphous alloy coatings with excellent anti-corrosion and anti-fouling properties offers a promising strategy to broaden the applications of amorphous alloys in marine fields. In this work, the superhydrophobic surfaces on the Fe-based amorphous alloy coatings with micro-nano hierarchical structures were fabricated using picosecond pulsed laser texturing (LT) and surface chemical modification. The fabricated superhydrophobic coating surfaces have achieved a maximum contact angle of 166.5°and a minimum sliding angle of 3.6°. Additionally, these produced coatings also demonstrate outstanding self-cleaning and anti-fouling properties for preventing surface contamination. The superhydrophobicity originated from the formation of micro-nano hierarchical structures and the grafting of organic compounds with low surface free energy on the LT fabricated surfaces. The changes in wettability were attributed to the differences in the solid–liquid interfacial area fractions. The electrochemistry tests revealed that the corrosion resistance of the produced coatings with superhydrophobic surfaces had improved considerably compared with the as-sprayed amorphous alloy coatings, which could broaden the functional applications of the Fe-based amorphous alloy coatings.

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.

Dissolution-induced oxide synthesis using SiO2 microparticles for oxide dispersion strengthening of Fe-based alloys

This study reports on a single-track laser surface alloying process that utilizes SiO2 powder to disperse both SiO2 particles and oxide inclusions in 316L stainless steel for oxide dispersion strengthening (ODS) purposes. In this process, the SiO2 powders partially dissolve in the melt pool, and the released silicon and oxygen atoms nucleate to form oxide inclusions in-situ within the metal matrix. This dissolution-induced oxide synthesis route demonstrated a high potential for ODS, achieving a high particle number density (6.6 × 104 mm−2) and area fraction (3.3%) comparable to that of bulk 316L samples produced via directed energy deposition. The hardness of the SiO2/316L composites reached a maximum of 232.4 HV compared to that of the 316L substrate (average 170.8 HV). The improvement in hardness was theoretically explained and quantified, significantly originating from the enhanced dislocation density strengthening mechanism resulting from the large difference in the coefficient of thermal expansion between SiO2 and 316L.

Fabrication and Properties of a Biodegradable Zn-Ca Composite.

In recent years, Zn and its alloys have become some of the most promising degradable metals as in vivo implants due to their acceptable biocompatibility and more suitable degradation rate compared with Mg-based and Fe-based alloys. However, the degradation rate of Zn-based materials after implantation in the body for orthopedic applications is relatively slow, leading to long-term retention of the implants after fulfilling their missions. Moreover, the excessive release of Zn2+ during the degradation process of Zn-based implants usually leads to high cytotoxicity and delayed osseointegration. To provide a feasible solution to the problem faced by Zn-based implants, a Zn-Ca composite was fabricated by an air pressure infiltration method in this work. The XRD pattern of the composite suggests that the composite is fully composed of Zn-Ca intermetallic compounds. The degradation tests in vitro show that the composite has a much higher degradation rate than pure Zn, and the high Ca content regions in the composite can preferentially degrade as sacrificial anodes. In addition, the composite can efficiently induce Ca-P deposition during immersion tests in Hank's solution. Cytotoxicity tests indicate that L-929 cells exhibit around 82% cell viability (Grade 1) even after being cultured in the 100% extract prepared from the Zn-Ca composite for 1 day and show excellent cell viability.

2D X-ray diffraction method for evaluating the local crystallization of Fe-based amorphous alloy ribbon induced by ultrashort pulsed laser local heating

Fe-based amorphous alloys, which exhibit excellent soft magnetic properties, are difficult to machine, owing to their high strength, toughness, and hardness resulting from their unique structures. The authors proposed a novel blanking method that improves the machinability by crystallizing only the local regions involved in machining, thereby reducing the local strength and toughness. Because the micro-region mechanical properties of amorphous alloys vary greatly depending on the precipitated crystal species and volume fraction, it is necessary to nondestructively investigate the type of microstructure achieved by local heat treatment to determine the appropriate blanking conditions. However, an appropriate method for investigating crystals precipitated locally in an amorphous matrix is yet to be established. In this study, we used the 2D X-ray diffraction method to investigate the local crystallization of an Fe-based amorphous alloy ribbon after local heat treatment using an ultrashort pulsed laser. Furthermore, the 2D method was used to investigate the residual stresses in the fully crystallized amorphous alloy ribbons, and the results were compared using the sin2(ψ) method. The 2D method detected the slightly precipitated crystals in a local area with a radius of about 40 µm in the amorphous matrix. The integrated intensity of the diffraction peaks can be used to predict the internal structure after local heat treatment. Furthermore, the 2D method could measure residual stress with smaller error than the sin2(ψ) method. The core-shell crystals precipitated by heat treatment exhibited a compressive residual stress of −82 MPa to −67 MPa in the core Fe3B crystals and tensile residual stress of 39–60 MPa in the shell α-Fe crystals, approximately. The residual stress values of the precipitated crystals depended on the direction of rotation of the quenching roll used in the production of the amorphous alloy ribbons.

Hardness prediction of the carbides in Fe-based multi-elements alloy by first-principles

Hardness prediction of the carbides in Fe-based multi-elements alloy by first-principles

Optimization of electromagnetic properties for soft magnetic powder cores prepared by gas-atomized FeSiBCuNb powders with continuously distributed the phase structures

The FeSiBCuNb gas-atomized powders (GAPs) show high sphericity, which is conducive to the formation of uniform insulating coating layers. However, it is difficult to obtain completely amorphous GAPs with relatively large particle sizes for Fe-based nanocrystalline alloys. In this work, the raw FeSiBCuNb GAPs with continuously distributed the phase structures are used to prepare soft magnetic powder cores (SMPCs). The effects of annealing process parameters on the average grain size, crystalline volume fraction, magnetic anisotropy constant (K), residual internal stress and magnetic properties of the SMPCs were studied in detail. The results showed that the increase of annealing temperature was more helpful for the magnetic properties of the SMPCs than extension of annealing time, which was due to average magnetic anisotropy constant (〈K〉) on coercivity primarily influenced on the SMPCs under the different annealing temperatures. When the annealing temperature is 500 °C, heating time is 50 min and holding time is 10 min, the NSMCs achieve relatively excellent magnetic properties: the effective permeability is 29.38 at 100 kHz, the quality factor is 126, the losses are 786 mW/cm3 (20 mT, 1 MHz), and the DC-bias characteristic is 67.28% (100 Oe or 7960 A/m). These results provided the potential for utilization of the raw FeSiBCuNb GAPs with continuously distributed the phase structures.

Effect of Warm Rolling on the Structure and Tensile Properties of a Metastable Fe-Based Medium Entropy Alloy

Effect of Warm Rolling on the Structure and Tensile Properties of a Metastable Fe-Based Medium Entropy Alloy

Effects of spark plasma sintering parameters on properties of Fe-based bulk amorphous alloys

Fe-based bulk amorphous alloys were prepared by spark plasma sintering (SPS) with different parameters. The thermal stability of Fe-based bulk amorphous alloys was characterized by differential scanning calorimetry (DSC) to determine the thermodynamic characteristic temperature, such as glass transition temperature (Tg) and crystallization temperature (Tx). X-ray diffraction (XRD), Archimedes drainage method, universal material testing machine, Electrochemical workstation and scanning electron microscope (SEM) were utilized to analyze the phase composition, relative density, compressive strength, corrosion performance, and fracture morphology and corrosion morphology of Fe based bulk amorphous alloys. This experiment show that Fe-based amorphous powder can be made into Fe-based bulk amorphous alloy with the size of φ12 × 9 mm by SPS technology. Meanwhile, the sample prepared with the parameters of sintering temperature of 560 ℃, sintering pressure of 550 MPa and the holding time of 1 min basically maintains the amorphous structure, and it has good compressive strength of 678 MPa, Microhardness of 1351.2 HV, density of 94.4 %, and perfect corrosion resistance.

Nanostructural evolution and improved magnetic performance of high saturation-induction Fe-based alloy via two-step combination crystallization

Refining nanoparticles and reducing the average random anisotropy constant (<K1>) are crucial for improving the magnetic properties of nanocrystalline alloys with high magnetic saturation induction. This study systematically investigates the evolution of nanostructure and soft magnetic performance during two-step combination annealing, which includes stress annealing at a flash heating rate followed by normal-annealing. Stress-annealing at 500 °C prior to crystallization reduces the area of the FeB-like short-range-order structure and effectively increases the number density of Cu clusters that act as heterogeneous nucleation sites for α-Fe(Si) nanoparticles. Stress-annealing at 500 °C precipitates tiny (∼ 5 nm) Fe3Si nanoparticles (A6 structure) dispersed in an amorphous matrix, resulting in more Fe clusters in the amorphous matrix and superior crystallinity following the second-step annealing process. The two-step combination annealing process increases the magnetic saturation induction (by ∼3%) and permeability (by∼62%) at 10 kHz in comparison with those obtained for the one-step annealed sample. Moreover, we propose a model for nanostructural evolution and the observed correlation with magnetic performances.

Improving the Surface Integrity and Tribological Behavior of a High-Temperature Friction Surface via the Synergy of Laser Cladding and Ultrasonic Burnishing

Quite a lot of engineering friction components serve at high temperatures, and are thus required to have excellent friction and wear resistance. The said study aims to fabricate high-wear-resistance coating on ordinary low-cost materials, achieving the low-cost manufacturing of some high-end friction components that are usually made with expensive solid alloys. The coating was prepared via laser cladding with a sort of widely used Fe-based self-fluxing alloy powder. The chosen substrate material was forged 42CrMo, which is popular in high-temperature friction engineering applications. In order to achieve the best possible high-temperature friction and wear properties, the prepared coating was turned and then ultrasonic burnished. Three samples, i.e., the substrate sample, the cladded sample without burnishing, and the cladded sample with burnishing, were prepared. For the three samples, the surface characteristics and friction properties at a 200 °C temperature were compared and investigated. According to the results, the cladded sample with burnishing exhibited the best surface finishing and friction behavior. Ultrasonic burnishing after cladding led to a further hardness improvement of 15.24% when compared with the cladded sample without burnishing. Therefore, ultrasonic burnishing is an effective low-cost post-treatment method for a wearable coating serving at a high temperature.

Investigation on pitting corrosion mechanism of the Fe-based amorphous alloy coating by three-dimensional X-ray imaging at micro-scale

Few work have been performed regarding the quantitative characterization of three-dimensional (3D) pitting corrosion process directly, although the corrosion behaviors and the passivation film stability of metals in various solutions have been studied heavily. The reported work quantitatively characterized the 3D pitting corrosion of the Fe-based amorphous alloy coating (Fe-based AAC) via X-ray micro-computed tomography (X-ray micro-CT) and further elucidated the mechanism of its pitting corrosion. Moreover, the microstructure and electrochemical performance of the Fe-based AAC have also been explored. The results showed that the targeted thermal sprayed Fe43Cr20Mo10W4C15B6Y2 coating was prone to be corroded with the increase of the hydrogen ion concentration, i.e. higher hydrogen ion concentration leads to poorer corrosion performance of the Fe-based AAC. The X-ray micro-CT results revealed that the pits in the Fe-based AAC initially nucleated below the pitting potential, and they also generated in the over-passivation stage. Furthermore, it was found that the corrosive medium does not penetrate into the coating/substrate interface, and the deduced corrosion mechanism from the findings was also discussed.

Influence of field-induced anisotropy on magnetic properties and domain structure of Fe-based nanocrystalline alloy via a new continuous magnetic field annealing furnace

Influence of field-induced anisotropy on magnetic properties and domain structure of Fe-based nanocrystalline alloy via a new continuous magnetic field annealing furnace

Application-Oriented Characterization and Analysis of Core Materials Under Medium-Frequency Condition

In medium-frequency applications, magnetic components generally operate in high-temperature conditions caused by higher power loss and more difficult heat dissipation, which results in changes in their electromagnetic characteristics. In this paper, the application-oriented characterization of the typical core materials, Mn-Zn ferrite and Fe-based nanocrystalline alloy, is comprehensively studied. The magnetic parameters under sinusoidal (5 kHz-50 kHz) and square (10 kHz) excitation from 20°C to 125°C is analyzed detailedly. Combined with the micromagnetic theory, the influence factors of electromagnetic parameters such as permeability and power factor angle are investigated. The loss variation of ferrite with temperature, flux density and frequency is explained by using the energy loss ratio. The proportion of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> and Pdy in total loss with temperature and frequency is compared, and the loss fluctuation of nanocrystalline alloys and ferrite is analyzed. Moreover, the reasonable range of frequency that needs to consider temperature effect in practical applications is suggested. The difference between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B-H</i> loop bias under asymmetrical square excitation and DC bias conditions is compared and illuminated. The effectiveness and limitation of typical Steinmetz Equations considering the temperature and duty cycle effect are analyzed, and the suggestion of loss calculation is given combined with the material characteristics.

Revealing the effect of rapid annealing on nano-crystallization behavior and soft magnetic properties of Fe–Co–B amorphous alloy

Rapid annealing (RA), or the application of a high temperature for a short duration, is an efficient strategy to promote the nano-crystallization of Fe-based amorphous alloys and improve their soft magnetic properties. Herein, the ternary Fe–Co–B amorphous alloy is investigated as a typical system to reveal the effect of RA on crystallization behavior and soft magnetic properties. It is found that the large superheating generated during RA significantly increases the homogenous nucleation rate of nanocrystals, while the short duration greatly inhibits the growth kinetics, yielding fine and dense nanograins in the amorphous matrix. The Fe–Co–B alloy shows optimized properties of low coercivity (5.6 A/m) and high saturation magnetization (1.87 T) after RA at 813 K for 3 s. In contrast, all superheating and long duration used in conventional annealing produce large and sparse grains with single crystal morphology and large coercivity above 30 A/m. This work reveals the thermodynamic and kinetic effects of RA on the nano-crystallization behavior of Fe-based amorphous alloys, showing that the RA treatment (high annealing temperature and short annealing time) can induce in-situ homogeneous nucleation and growth, which may help guide the design of Cu-free amorphous/nanocrystalline alloys with desirable soft magnetic properties.

Hetero-deformation induced strengthening, precipitation hardening, and metastability engineering in a novel maraging Fe68Ni10Mn10Co10Ti1.5Si0.5 medium entropy alloy

In the present study, the concept of maraging characteristics has been manipulated using a multistep thermo-mechanical approach involving isothermal aging and reversion treatments. Accordingly, a novel metastable maraging Fe68Ni10Mn10Co10Ti1.5Si0.5 (at%) medium entropy alloy has been designed and microstructurally engineered to achieve a heterogeneous medium entropy alloy decorated by (NiMn)3−xTix and ƞ-Ni3Ti nano-precipitates. Remarkably, the alloy exhibited an ultra-high yield strength of ∼1.3 GPa with a total elongation of ∼25.3% in the partially reversed sample, attributed to several aspects of microstructural heterogeneities, including the dual-phase microstructure, compositional gradient heterogeneity, and nano-precipitates. We proposed a prospective direction for the development of high-performance materials for structural applications through the microstructural engineering of Fe-based medium entropy alloy.

Chemical Etching, Thermally Driven Combination Strategy to Fabricate Superhydrophobic Fe-Based Amorphous Coatings with Excellent Anticorrosion Property: Based on Hydroxylation Effect.

Fe-based amorphous coatings are ideal materials for surface protection due to their outstanding mechanical properties and corrosion resistance. However, coating defects are inevitably formed during the preparation of coatings by thermal spray technology, which seriously affects the corrosion performance. Inspired by bionics, conceiving superhydrophobic surfaces with liquid barrier properties has become a new idea for the corrosion protection of metal surfaces. In this work, based on surface hydroxylation, we designed a superhydrophobic Fe-based amorphous coating with corrosion resistance by chemical etching combined with a thermally driven preparation strategy. The obtained superhydrophobic coatings exhibit liquid repellency (contact angle >150°) and excellent corrosion resistance (corrosion current density and passive current density reduced by 3 orders of magnitude). The results revealed that the superhydrophobic behavior stems from the construction of hydroxyl-induced surface micro-/nanomultilevel aggregates (cluster structures). The hydrophobic agent layer deposited on the surface of cluster aggregates and the nanoparticle elements that constitute the clusters dominate the corrosion resistance of the coating. This work provides an effective guide to the design of high-corrosion-resistant Fe-based amorphous alloy coatings and promotes their engineering applications.