Iron-based Alloys Research Articles

Direct graphene growth on low-alloy and mild steel surfaces controlled by carbon solubility and surface microstructural transformations during chemical vapor deposition

This study demonstrates for the first time, graphene grown directly on the iron-rich surfaces of bulk 8620 low-alloy and 1018 mild steel by chemical vapor deposition, a key step toward developing thin graphene coatings with strong graphene-steel bonding. Low growth temperatures of 660 °C–680 °C, were used to manipulate the steel's carbon solubility, confining carbon diffusion and microstructural transformations to the surface regions, with the bulk relatively unchanged. For 1018, a growth temperature of 680 °C resulted in a multilayer graphene coating with 80 % coverage. The alloying elements in 8620 improved graphene formation by influencing the surface microstructure transformations at these growth temperatures, with graphene coverage up to 95 %. The surface microstructure for 8620 affected graphene formation, seen in growths at 660 °C where a few-layer graphene coating formed from a cementite surface layer, and for growths at 680 °C where multi-layer graphene covered a pearlite dominant surface microstructure. Contact angle measurements confirmed the hydrophobicity of the graphene coating and electrochemical testing by potentiodynamic polarization and electrochemical impedance spectroscopy confirmed the 101 mV improvement to corrosion potential and an increase in impedance up to 18.23 kΩ. These detailed results regarding the direct growth of graphene as a coating layer on highly oxidation-sensitive steel surfaces suggest that this process is achievable through manipulating carbon solubility at the steel's surface by controlling temperature, alloy composition and surface microstructure transformations. These methods could be leveraged in developing protective graphene coatings for various iron-based alloys.

Effect of elevated temperature on the bond behaviour of adhesive shear joints between glass substrate and iron-based shape memory alloy strip

Glass has been increasingly used as structural elements, such as glass beams or fins. Previous feasibility studies have shown increased initial and post-fracture load-bearing capacity of laminated glass beams post-tensioned with adhesively bonded iron-based shape memory alloy (Fe-SMA) strips. However, the potential elevated service temperatures were not considered, which significantly degraded the material properties of the adhesive. This study experimentally investigated the mechanical behaviour of Fe-SMA-to-glass lap-shear joints with an epoxy adhesive at different temperatures of 23 °C, 50 °C, and 80 °C, representing room temperature and typical elevated service temperatures. The results showed that, compared with the one at room temperature, the load-carrying capacity remained nearly unchanged at 50 °C and decreased by approximately 20% at 80 °C. On the contrary, the effective bond length increased from approximately 116mm to 250-300mm. The failure modes, the tensile strain of the iron-based shape memory alloy, the bond-slip behaviour, and the fracture energy of the joints were also evaluated. The current study fills a significant research gap in the engineering application of strengthening glass structures by bonded pre-stressed Fe-SMA strips. Moreover, the results may also significantly contribute to the future application of the selected adhesive at elevated temperatures.

Analytical model for RC beams with embedded prestressed Fe-SMAs

Prestressed iron-based shape memory alloy (Fe-SMA) strengthening is an effective means to enhance the performance of reinforced concrete (RC) structures. The applied prestress level significantly influences the strengthening efficiency. However, the absence of a reliable model predicting the applied prestress hinders the efficient design of prestressed Fe-SMA strengthening solutions. To fill this gap, the current study proposes an analytical model, with which a constant zone and a transfer zone are identified in strengthened RC beams. The constant zone, with zero interfacial shear stress, sustains a constant prestress level, while the transfer zone, experiencing non-zero shear stress, gradually reduces the Fe-SMA tensile stress from the prestress level to zero. Validated through experiments, the proposed model accurately predicts the applied prestress levels and prestress-induced deflections in RC beams strengthened with Fe-SMAs and more conventional carbon fiber reinforced polymers (CFRPs). Further analysis reveals that the transfer zone length ranges from 4 to 7 characteristic lengths, and it is proportional to the logarithm of the applied prestress level. Simplifying a constant prestress level within the beam span yields sufficiently accurate prestress analysis.

Enhancing magnetostriction in FeAl alloys via crystal growth orientation tuning by a trace amount of Pt doping

Iron-based cubic alloy systems opened the door to the development of magnetostrictive materials with moderate magnetostriction, low cost, and good mechanical properties. At the as-cast state, the grain growth orientation of these alloy systems is close to random, which deteriorates magnetostriction. Doping with certain elements can tune the growth orientation to enhance magnetostriction. However, the driving force for the crystal growth along preferential orientation is still not clear. Here in this work, revealed by density functional theory (DFT) calculation, Pt doping can tune the crystal growth direction of FeAl along <100> crystal direction (same as easy magnetization direction), which can be utilized to realize 90° domain-switching and thus magnetostriction is enhanced greatly. These are confirmed by experimental results. The magnetostriction increases from 29 ppm to 80 ppm, representing a 176% enhancement through doping with 0.4 at.% Pt. The maze magnetic domain structures, observed by magnetic force microscope, are also preferentially <100> oriented and feature stripes. In consideration of the similarity between this study and our previous study on FeGa alloy (C. Zhou et al., 2020), it can be expected that our methods can be extended to other magnetostrictive materials and help develop polycrystals with desired orientations.

Radiation Shielding Properties of Nickel, Copper and Iron Based Alloys

This study explores the radiation shielding properties of Iron-based and Nickel-based alloys with Cobalt composition to evaluate their performance in photon attenuation and shielding applications. The objectives of this work are to determine linear and mass attenuation coefficients (LAC, MAC), half and tenth value layers (HVL, TVL), mean free path (MFP), effective atomic number and electron density (Zeff, Neff), effective conductivity (Ceff), atomic cross section (ACS) and electronic cross section (ECS) of nickel and iron base alloy with Cobalt using Phy-X/PSD within 0.001 MeV to 10 MeV. The result shows Iron and Nickel-based alloys have electron densities around 10²³ electrons per gram, with increased Iron concentration improving low-energy photon attenuation. Nickel-based alloys have a higher MAC and LAC compared to Iron-based oxides, indicating better photon absorption per unit mass and thickness, respectively. Nickel-based alloys exhibit a lower HVL and TVL, indicating greater attenuation and absorption efficiency for photons, especially at lower energies. Conversely, Iron-based alloys, while showing higher HVL and TVL. Nickel-based alloys exhibited higher electron densities the Iron-based alloys and Zeff values for Nickel based alloys, ranging from 27.1 to 27.8 while Iron-based alloys with Zeff between 26.2 and 26.8. Ceff in Iron-based alloys was stable at (1.50 to 1.74) x 10⁹ S/m, while Nickel-based alloys showed significant fluctuations below 0.01 MeV. Nickel-based alloys also had higher ACS and ECS, indicating superior photon interaction, especially at lower energies. These results highlight Nickel based alloys' greater efficacy in low-energy photon attenuation and the stable performance of Iron based alloys at higher energies.

Severe plastic deformation of Zn and Zn-based alloys

There has been much research on zinc and its alloys for being used in different industries and applications, mainly due to their low cost, availability, good wear resistance and mechanical properties. Moreover, zinc alloys have emerged as the latest advancement in the field of biodegradable metals, offering a more sustainable option with their moderate corrosion rate when compared to other biodegradable metals like magnesium and iron-based alloys. Nevertheless, mechanical properties of zinc alloys typically fall below the necessary levels for use in load-bearing implant applications. In this regard, severe plastic deformation serves as a distinctive technique to enhance the mechanical characteristics of zinc-based alloys, all while keeping the chemical composition intact. In addition to mechanical properties, and as is discussed in this article, SPD can affect other properties of Zn alloys, including biological and corrosion behavior. Over the past few years, extensive studies have been conducted to explore how various SPD processes impact the properties of zinc and its alloys. In this study, the main effects of SPD on the microstructure, mechanical properties, superplastic behavior, and corrosion of zinc and zinc allots together with the underlying mechanisms are reviewed.

Experimental insights on iron-based alloys corrosion in water cooled loops

This paper presents experimental findings on the behavior of iron-based alloys in environmental conditions typical of nuclear fusion technology, specifically focusing on material degradation, which is a critical aspect for the water cooling system of EU DEMO breeding blankets. The experimental campaign investigates potassium hydroxide’s role as an alkalizing agent, testing various concentrations to assess its impact on corrosion resistance. Additionally, it examines how oxygen levels affect localized corrosion development, which is crucial for mitigating corrosion risks in fusion applications. Seven 1000-hour tests were conducted to determine optimal conditions for corrosion reduction. Findings include identifying an oxygen concentration threshold to prevent piping cracking on EUROFER97 specimens.

Characterization of low-temperature creep and stress relaxation of an iron-based shape memory alloy (Fe-SMA) using in-situ synchrotron diffraction

Iron-based shape memory alloys (Fe-SMAs) are e-merging materials with extensive application in civil structures owing to their unique properties, including the shape memory effect. However, it is crucial to understand the time dependent behavior of Fe-SMAs for their effective application as pre-stressing element. In particular, behavior at individual stress, the underlying mechanism, and the transformation kinetics have not been investigated yet. To address these important fundamental research gaps, in-situ compression creep and stress relaxation experiments with high-energy X-ray diffraction (HEXRD) of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) Fe-SMAs were conducted. The time-dependent behavior of the Fe-SMA was investigated at different stress levels with respect to the yield strength (YS) at room temperature. The experimental result showed that the material exhibits a creep strain of up to 1.84 % and 56 MPa relaxed stress at test stress of 769 MPa (1.6 σYS) within one hour of holding. Stacking fault probability and phase volume fraction quantification provide an understanding of the mechanisms based on different stress levels. The transformation kinetics traced from the characteristics of HEXRD peaks offer further insights on creep depending on the contribution of {hkl} families. The paper concludes with an evaluation of the existing models for predicting creep and stress relaxation of Fe-SMA.

Perspectives on Adhesive–Bolted Hybrid Connection between Fe Shape Memory Alloys and Concrete Structures for Active Reinforcements

The prestressed active reinforcement of concrete structures using iron-based shape memory alloys (Fe-SMAs) is investigated in this experimental study through three connecting methods: adhesive–bolted hybrid connection, bolted connection, and adhesively bonded connection by activating at elevated temperatures (heating and cooling) and constraining deformation to generate prestress inside Fe-SMAs, through which compressive stress is generated in the parent concrete structures. In tests, the Fe-SMA is activated at 250 °C using a hot air gun, generating a prestress of 184.6–246 MPa. The experimental results show that local stress concentration in the concrete specimen and Fe-SMA plate around the hole is caused by the bolted connection. The adhesively bonded connection is prone to softening and slip of the structural adhesive during the activation process, thereby reducing the overall recovery force of Fe-SMAs. The adhesive–bolted hybrid connection effectively mitigates the local stress concentration problem of concrete and Fe-SMAs at anchor holes, while avoiding the prestress loss caused by the softening and slip of structural adhesive during elevated-temperature activation, achieving good reinforcement effect. This study on the connection methods of an Fe-SMA for reinforcing concrete structures provides both experimental support and practical guidance for its engineering application, offering new perspectives for future research.

Python-based numerical study on bolted joints between Fe-SMA and steel plates for structural reinforcements

In order to rehabilitate the performance of deteriorated steel structures, the active prestressed reinforcement employing new intelligent material, Iron-based shape memory alloy (Fe-SMA), has received extensive attentions. To reveal the mechanical properties of bolted joints between Fe-SMA and steel plates, a parametric method to establish finite element model via secondary development of ABAQUS based on Python scripts was proposed. It greatly reduces modelling costs and improves modeling efficiency. Besides, the proposed numerical models were verified against the experimental results by failure mode, final deformation, load-displacement characteristics, ultimate load-bearing capacity and initial stiffness. It is demonstrated that the numerical simulation results are in good agreement with the experimental results. What is more, a parametric study on thickness and geometry of steel plates, as well as the end distance, edge distance and thickness of Fe-SMA plate was conducted to verify the applicability of current leading specifications for steel structures. It is evident from the results that the thickness of Fe-SMA should be controlled to prevent failure of parent steel structures. Furthermore, similar to steel plates, the thickness of Fe-SMA plate can be considered linear and the failure of bolt can be avoided, as described in Chinese code GB 50017–2017 and Eurocode 3 Part 1–8. However, the minimum allowable edge distance in Chinese code GB 50017–2017 and the ultimate load-bearing capacity calculated by Eurocode 3 Part 1–8 is conservative for bolted joints between Fe-SMA and steel plates. Hence, it is urgent to formulate design specifications for this kind of bolted joints for the scientific and economical application of Fe-SMA in structural active reinforcements.

Experimental investigation on shear behavior of I-shaped concrete beam with Fe-SMA rebars

Vertical prestress loss causes cracking in prestressed box-girder bridge webs. As a new type of prestressed material, iron-based shape-memory alloy (Fe-SMA) rebars can be used as vertically prestressed rebars to compensate for the loss of vertical prestress in box-girder webs. In this study, box-girder webs were simplified into I-shaped beams, and the shear performance of these I-shaped beams with vertical Fe-SMA rebars in the shear span was analyzed to estimate the feasibility of using Fe-SMA rebars. The effects of the activation state, layout spacing, and rebar diameter on the shear performance of the I-beams were explored. The variations in the cracking load, ultimate load, and main tensile strain were systematically investigated. The results indicate a significant transformation from brittle to ductile bending shear failure following Fe-SMA activation. Moreover, the ultimate deflection exhibited a significant increase exceeding a factor of 2. The activation of the Fe-SMA was beneficial for delaying specimen cracking and improving shear strength. Specifically, the shear cracking and ultimate loads increased by 24.21 % and 12.11 %, respectively. Simultaneously, the activation of the Fe-SMA rebar significantly reduced the primary tensile strain within the shear span segment and effectively delayed crack development. The diagonal fracture width of the specimens with the activated Fe-SMA was significantly reduced (67.24 %, 57.14 %, and 52.22 %, respectively) at three different stress settings (400, 450, and 500 kN). Furthermore, a methodology for estimating the shear cracking and bearing capacity of I-beams with vertical Fe-SMA rebars is proposed. The calculated values are in excellent agreement with the experimental data, thereby serving as a valuable reference for future research.

Shear and bonding performances between Fe-SMA and steel for strengthening of steel structures

Iron-based shape memory alloy (Fe-SMA) has been employed in China and the Czech Republic to reinforce steel bridges due to its outstanding self-prestressing characteristics. Nevertheless, the lack of theoretical guidelines necessitates this study to align with the practical Fe-SMA-reinforced applications in civil engineering. This study experimentally investigates the shear performance and load-transfer mechanism of 45 Fe-SMA/steel adhesive joints. Specifically, the shear characteristics of the adhesive joints affected by the various parameters of bonding layer thickness, steel plate thickness, bonding length and adhesive type are explored, the failure mode and load-displacement relationship are assessed, and some suggestions for optimization design are proposed. The experimental results demonstrate that the Fe-SMA/steel adhesive joints experiencing interface failure exhibit a linear load-displacement relationship. Contrarily, the load-displacement relationship of the adhesive joints under cohesive failure modes contains a yield segment. Longer bonding length results in more considerable failure evolution distances for Sika S02 and LPdur 03 specimens with cohesive failure, indicating better ductility of these specimens. Additionally, the epoxy adhesives of Sika S02 and LPdur 03 are preferred while employing Fe-SMA plates for bonding reinforcement of steel structures, which can maximize the characteristics of Fe-SMA to obtain stable and superior reinforcement performance. The experimental achievements have remarkable potentials for improving the in-service performance of old and damaged steel structures and other infrastructures.

Bond-slip models on interfacial behavior between Fe-SMA and steel in hygrothermal environments

Strengthening the existing steel structures to enhance performance can prolong their service life and reduce carbon emissions. Previous studies have employed iron-based shape memory alloy (Fe-SMA) to adhesively and actively retrofit long-span steel bridges in practice, achieving satisfactory repair efficiency. Nonetheless, concerns persist regarding the long-term performance of Fe-SMA-bonded parent structures, principally stemming from the performance degradation of the adhesives in hygrothermal environments. In this study, the damage evolution and debonding mechanisms of Fe-SMA/steel single-lap joints (SLJs) in hygrothermal environments are investigated through 54 lap-shear tests. The evolutionary process of Fe-SMA strain and shear stress within the overlapping zone is assessed, varying with aging time and adhesive type under shear load. Furthermore, the bond-slip models of the Fe-SMA/steel SLJs are put forward, which change with the aforementioned influencing factors in hygrothermal environments. The lap-shear tests demonstrate that the ultimate shear stress of SLJs is transmitted approximately up to 50 mm away from the initial end, with shear stress developing swiftly towards the free end during this phase. In hygrothermal environments, the effective overlapping length of the SLJs is highly contingent on the material properties of adhesives, improving with the prolonged aging time. This study proposes bond-slip models that describe the interfacial performance between Fe-SMA and steel, accounting for the detrimental influence of temperature, humidity, plastic deformation of components and strain relaxation. The experimental outcomes can guide the analysis of the debonding characteristics of Fe-SMA-bonded structures, and the theoretical study can provide reliable predictions for the service performance of reinforcement systems in hygrothermal environments.

Shear Retrofitting Effect of Self-prestressed Iron-based Shape Memory Alloy for Reinforced Concrete Beams

Shear Retrofitting Effect of Self-prestressed Iron-based Shape Memory Alloy for Reinforced Concrete Beams

Magnetic shielding properties of an iron-based nanocrystalline alloy for induction heating systems

A nanocrystalline alloy, with an iron-based composition (Fe58.5Si16.7B6.5Nb5.1Cu13.2) and a Curie temperature of 570 °C, was investigated for its effectiveness as magnetic shielding films in an induction heating system. The primary focus of the research was to evaluate the shielding performance of the 3-turned (9-layered) shielding films with dimensions of 135 mm × 17 mm × 0.15 mm. Upon winding, these films formed a cylindrical structure that enveloped the coil, with a diameter of 13.9 mm and a height of 17 mm. The results showed that increasing the degree of fragmentation within the nanocrystalline shielding films significantly reduced the magnetic permeability by decreasing the real component from 11,500 to 400 and the imaginary part from 2800 to 20. However, a lower degree of fragmentation led to a 10 % increase in the resistance (Rs) of the heating module, although this effect was less pronounced as the relative permeability continued to increase. Furthermore, observations on preheating time to a set temperature of 400 °C and total energy consumption over a duration of 250s revealed an initial downward trend, followed by a rapid increase that even exceeded the initial values as the magnetic permeability of the nanocrystalline shielding films augmented. Notably, the study emphasized that nanocrystalline shielding films with a relative permeability value of 1000 demonstrated exceptional magnetic shielding performance, resulting in a 12.5 % reduction in preheat time and 7 % less energy consumption during preheating. In addition to empirical findings, the study developed a theoretical model elucidating the shielding mechanism inherent in induction heating systems. This model serves as a robust framework for the application of nanocrystalline shielding materials in such systems, laying the groundwork for enhanced magnetic shielding capabilities in future applications.

A Review of Additively Manufactured Iron-Based Shape Memory Alloys

A Review of Additively Manufactured Iron-Based Shape Memory Alloys

Surface Modification of Chromium–Nickel Steel by Electrolytic Plasma Nitriding Method

Electrolytic plasma nitriding is an attractive chemical heat treatment used to improve the surface properties of steel by implementing nitrogen saturation. This method is widely applied to steel and iron-based alloys operating under various operating conditions. In this work, using liquid-phase plasma nitriding technology, a nitrided layer was obtained on the surface of 40CrNi steel in electrolytes of different concentrations. The microstructure and phase composition of the nitrided layer were investigated and analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and we performed Vickers hardness and wear resistance tests using the ball-on-disc method. The microhardness and wear resistance of nitrided 40CrNi steel were significantly improved due to the lubricating properties of the ε-Fe2N phase formed on its surface.

Magneto-mechanical hysteresis damping mechanism in dual-phase iron-based alloy with zero magnetostriction

Magneto-mechanical hysteresis damping (MMHD) is usually positively correlated with their measured magnetostriction, but this correlation becomes ambiguous in negative magnetostriction and multiphase materials. This work found that even if saturated magnetostriction of Co-20Fe alloy is zero, its MMHD value can still be as high as 0.015. Analysis revealed that the MMHD correlates with phase percentages and the absolute parallel magnetostriction values of phases. In multiphase alloys, measured magnetostriction cannot be directly used to assess damping. High nonmagnetic damping in Co-15Fe alloy with fcc structure is due to distributed misfit dislocations. This research sheds light on damping mechanisms in multiphase ferromagnetic alloys.

Cavitation erosion performance and phase transformation strengthening behavior of laser clad iron-based shape memory alloy coatings

In order to avoid cavitation damage on the surface of overcurrent components after long-term service, the surface is reinforced with a coating to improve its cavitation resistance, thus prolonging service life. The present study employed analytical techniques, such as X-ray diffractometry (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), to investigate the cavitation erosion performance of laser clad Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) coatings with focus on the enhancing mechanism of their martensitic phase transformation. The results indicated that laser cladding could produce high-quality SMA coatings, free of defects such as pores and cracks, resulting in a significant improvement in the cavitation erosion performance. After 5 h of the cavitation, the coated samples remained in the cavitation erosion incubation stage, demonstrating an accumulated mass loss rate of approximately 0.12 mg/h, merely 13 % of that observed in the matrix samples. Extensive microstructural delamination occurred in the matrix samples after 5 h of the cavitation, whereas the coated samples exhibited only "shear bands" formed by plastic deformation on the surface. The martensitic phase transformation from γ-austenite to ε-martensite served to dissipate the stress induced by cavitation bubble collapse on one hand, and, on the other hand, the robust nature of martensite produced a hardening effect, significantly enhancing the cavitation resistance of the coating.

An activation guideline for the resistive heating process of iron-based shape memory alloy embedded in concrete

In new and existing reinforced concrete (RC) structures, extensive research has proven that iron-based shape memory alloys (Fe-SMA) can be used as prestressing materials. As for the Fe-SMA embedded in concrete, the resistive heating method is usually adopted to activate its shape memory effect to develop prestress in the concrete. The prestressing process of the Fe-SMA involves multiple physical fields such as electric currents, temperatures, and mechanics. An accurate and standardized implementation of the activation process is essential for the Fe-SMA to effectively generate the expected prestress in the structure. However, data drift can occur when thermocouples measure the temperature of the Fe-SMA through which current flows and non-contact heat sensors can not measure the temperature of the Fe-SMA embedded in the concrete. It is also difficult to theoretically estimate the activation time and temperature of the Fe-SMA in concrete. The pre-test or empirical values are usually required to estimate the activation current and time for reaching the target temperature, compromising the construction efficiency. Additionally, the selection of activation parameters varies wildly for Fe-SMA with different specifications and sizes. There are currently no standardized guidelines for the electrical resistive activation of the Fe-SMA. Therefore, a multi-physical finite element model was developed to study the self-prestressing process of the Fe-SMA embedded in concrete and predict the temperature distribution and prestress of the Fe-SMA and concrete. The effects of the current density, the Fe-SMA shape and size, and the concrete cover depth were analyzed. In the end, an activation guideline for the electrical resistive heating of the Fe-SMA was offered to facilitate the construction and activation process in field engineering.