Iron-Based High-Temperature Alloys: Alloying Strategies and New Opportunities

Abstract

Iron-based high-temperature alloys are engineered to withstand extreme conditions, including elevated temperatures, mechanical stress, and corrosive environments. These alloys play a critical role in industries such as aerospace, power generation, and chemical processing, where materials must maintain structural integrity and performance under demanding operational conditions. This review examines recent advancements in iron-based alloys, with a focus on alloying strategies, high-temperature performance, and applications. Traditional approaches—including alloy design, microstructure control, process optimization, and computational modeling—continue to enhance alloy performance. Furthermore, emerging technologies such as high-entropy alloy (HEA) design, additive manufacturing (AM), nanostructured design with nanophase strengthening, and machine learning/artificial intelligence (ML/AI) are revolutionizing the development of iron-based superalloys, creating new opportunities for advanced material applications.

1. Introduction

Advanced high-temperature materials encompass several key categories: high-temperature alloys (HTAs, also known as superalloys) [1,2], refractory metals [3], ceramics, intermetallic compounds, metal matrix composites, ceramic matrix composites, C/C composites, and gradient functional materials [4,5]. These materials are critical for industries operating under extreme conditions, including aerospace, automotive, power generation, and industrial manufacturing [6,7,8]. High-temperature (HT) materials are specifically engineered to endure mechanical stress, thermal cycling, oxidation, and corrosion at elevated temperatures [9,10]. Among these, HTAs have become the most widely adopted due to their exceptional thermal stability, good machinability, outstanding mechanical properties, and superior resistance to oxidation and corrosion at high temperatures [1,2,8,11]. Designed to maintain mechanical strength and structural stability at temperatures typically above 600 °C, HTAs are crucial for extreme environments where conventional materials would fail under intense heat, pressure, or chemical exposure [12]. These alloys are primarily based on nickel (Ni) [13], cobalt (Co) [14], iron (Fe) [11], or titanium (Ti) [15], and are frequently alloyed with chromium (Cr), molybdenum (Mo), and aluminum (Al) to enhance their thermal and mechanical properties.

HTAs are classified into three primary categories according to their dominant metallic base: Fe-based, Co-based, and Ni-based superalloys (Figure 1a) [16,17,18]. Among these, Ni-based alloys currently represent the most extensively utilized category [16], prized for their exceptional heat resistance and oxidation stability, which make them indispensable for aerospace (Figure 1b) and power generation applications [19]. Their remarkable strength primarily derives from the formation of a protective oxide layer that effectively prevents further material degradation.

Co-based alloys demonstrate superior performance in high-wear environments and are commonly employed in turbine blade applications [14]. In comparison, Fe-based alloys offer a cost-effective alternative [20], and are typically employed in less extreme conditions than nickel or cobalt alloys while still maintaining considerable heat resistance.

The selection of HTAs is governed by application-specific requirements including operating temperature ranges, mechanical stress conditions, and environmental exposure. A critical consideration involves balancing performance requirements with cost-effectiveness. Among the available options, Fe-based HTAs distinguish themselves through compelling advantages, most notably their exceptional cost efficiency. Given the natural abundance of Fe and its significantly lower cost compared to nickel, cobalt, or titanium, Fe-based alloys emerge as the preferred solution for large-scale industrial applications [17,21,22,23,24,25,26,27,28,29], where material costs substantially influence technological and economic feasibility. Beyond their economic advantages, Fe-based HTAs deliver competitive HT performance, exhibiting excellent strength retention, creep resistance, and fabrication ease [21,22]. These alloys demonstrate superior manufacturability, including enhanced weldability [30,31,32], casting characteristics [33,34,35], and good formability [36], along with compatibility with advanced coating technologies [37,38] and material functionalization methods [39,40,41]. Such comprehensive processability often surpasses that of nickel- or cobalt-based superalloys, particularly in machining operations and joining processes [42,43,44,45], making them more practical for industrial-scale manufacturing.

Research interest in Fe-based alloys, as evidenced by the publication trends shown in Figure 1c,d, demonstrates consistent growth, with a clear evolution from traditional research themes like steel metallurgy, mechanical properties, and microstructural analysis toward emerging frontiers such as shape memory alloys, powder metallurgy techniques, amorphous material development, activity coefficient studies, and hyperfine interaction investigations. The properties of Fe-based HTAs can be precisely engineered through strategic alloying with elements such as Cr, Ni, Mo, Al, and Si [23,46,47], enabling tailored improvements in oxidation resistance and mechanical stability under extreme operating conditions. This adaptability renders them suitable for demanding applications including gas turbine components [19,48], HT exhaust systems, steam power generation infrastructure [46], and nuclear reactor pressure vessels [35].

The selection of Fe-based alloys for this review is justified by their exceptional cost–performance ratio, versatile processability, and rapid technological advancements. Moreover, emerging strategies such as high-entropy alloy design, additive manufacturing techniques, and machine learning-assisted development are transforming the field of iron-based superalloys. This review synthesizes advances in iron-based high-temperature alloys while addressing key challenges and opportunities to guide future breakthroughs in extreme environment performance.

2. Alloying Strategies

Fe-based alloys are classified based on their primary alloying element (Me), structure, and intended application. This section focusses on the influence of alloying elements. The performance of Fe-based HTAs is heavily influenced by the choice of alloying elements. The key elements commonly used in Fe-based alloys are chromium (Cr) [49,50,51], aluminum (Al) [52,53,54,55], silicon (Si) [56,57,58], nickel (Ni) [59], and zirconium (Zr) [60]. Besides these, other elements such as molybdenum (Mo) [61], vanadium (V), cobalt (Co), titanium (Ti), Tungsten (W), and manganese (Mn) [62,63] are also used to optimize the high-temperature properties of Fe-based alloys. Nitrogen (N) also plays a crucial role in the nitriding of Fe-based alloys, where alloying elements like Ti, V, Al, Si, Cr, and Mo form nitrides (MeNx) in the matrix. The resulting properties of the nitrided alloy depend on the alloy composition, the crystal structure [64] and morphology of the nitrides, and the nitriding depth, as summarized by Steiner and Mittemeijer [65].

Du et al. [66] provide a concise overview (Figure 2a) of how fundamental alloying elements—C, P, S, Si, and Mn—affect the microstructure and mechanical properties of iron-based alloys. Among them, C plays a crucial role in both ironmaking and steelmaking processes due to its essential function as a reductant in the extraction of iron from its ores. Moreover, carbon significantly influences the microstructure, mechanical properties, and HT behavior of Fe-based alloys, making it a key factor in determining their performance [67,68]. Fe-based HTAs can be classified based on their carbon content into three main categories: low-carbon alloys, medium-carbon alloys, and high-carbon alloys. Low-carbon alloys excel in oxidation resistance and thermal stability, making them ideal for components exposed to high-temperature gases. Wear resistance increases with carbon content for Fe-based HTAs (such as martensitic secondary hardening steels) [69]. Artificial intelligence and machine learning (AL/ML)-driven alloy research is gaining significant attention [2]. By leveraging data-driven modeling, AI/ML accelerates the prediction of Fe-based alloy properties and optimizes compositions [70,71,72,73]. In the context of iron–carbon alloying design strategies (Figure 2b), the application and development of machine learning methods in phase structure identification, process parameter optimization [74], and mechanical properties optimization based on composition and microstructure, as well as the composition inverse design technology and surface damage detection method of iron and steel materials, have been thoroughly introduced and discussed [72]. Further, fundamental alloying elements and other features are used as input parameters and then trained through a backpropagation neural network model, as shown in Figure 2c [66,72].

The introduction of Cr and Al can enhance the oxidation resistance by forming a protective oxide layer on the surface, which is crucial for high-temperature applications like gas turbines and exhaust systems [49,52]. The addition of Si improves the overall resistance to oxidation, and increases the strength of the alloy at high temperatures [75]. Cast irons with a high silicon level are widely used when equipment is being handled in sulfuric acid environments. Though primarily a component in nickel-based alloys, small amounts of Ni are sometimes added to Fe-based alloys to improve thermal stability and creep resistance. Further, the refractory metals (Mo, W, and V) enhance the high-temperature strength, creep resistance, and overall thermal stability of the alloys [75,76], which is also critical for maintaining structural integrity under prolonged high-temperature stress. Moreover, Yang et al. [35] found that the solute elements (Mn, Ni, Si) played an important role in the grain structure, hardness, irradiation hardening, and defect clustering behavior of Fe-based model alloys.

The incorporation of rare earth metals has been demonstrated to significantly enhance the performance characteristics of high-temperature alloys [54,77,78,79,80]. A notable example is shown in the work of Qi et al. [77], who established that yttrium (Y) additions markedly improve high-temperature steam oxidation resistance in FeCrAl alloys. This enhancement primarily occurs through the stabilization of the protective surface oxide film. The same research group further investigated this phenomenon through first-principles calculations [81], revealing the atomic-scale mechanisms by which Y improves oxidation resistance. Their theoretical analysis complemented the experimental findings, providing fundamental insights into the role of Y in surface oxide stabilization.

As for the alloying of Fe-based alloys, significant attention has been paid to the synergistic effects of various alloying elements [82,83]. These synergistic interactions, achieved through the careful selection and combination of two or more elements, are essential for optimizing the performance of the alloy [84]. Each alloying element contributes distinct properties, but their combined effects often result in enhanced mechanical, thermal, and chemical characteristics that surpass the individual contributions of each element. For instance, Cr is frequently used in Fe-based alloys to enhance oxidation and corrosion resistance by forming a stable, protective Cr₂O₃ layer on the surface. When combined with Al [85], Mn [86], and Si [47], the protective effect is amplified. The synergistic interaction of Cr and Al extends the durability of the alloys in harsh environments [87,88], known as Fe–Cr–Al alloys [61,89,90,91], making them suitable for applications such as catalyst support [24], as well as cladding in nuclear reactors [23,92], gas turbines [93], and heat exchangers [94].

The synergistic combination of Ni and Mo significantly enhances creep resistance and solid solution strengthening in Fe-based alloys. Ni improves thermal stability and fracture toughness [59], while Mo enhances the resistance to deformation under prolonged high-temperature stress [76]. When alloyed with Cr and/or Ni, Co further contributes to improved HT strength and oxidation resistance [95]. Studies have demonstrated that Cu [63,96], Al [63,97], Mn [63], Ti [22,98] and Mo [95,99] effectively promote precipitate formation, further optimizing alloy performance. These precipitates serve as potent obstacles to dislocation motion, significantly enhancing strength and creep resistance. For instance, Ti and Mo enhance high-temperature strength and creep resistance by refining grain structures and stabilizing precipitates [100]. Another notable example is the strategic incorporation of Ti and V with other alloying elements [101]. Ti facilitates grain refinement and stabilizes carbide/nitride formation, while vanadium strengthens the alloy via fine vanadium carbide precipitates [76,101]. These elements collectively stabilize the microstructure by promoting the formation of beneficial intermetallic phases, including Ni(Al, Fe) [102], NiAl [103,104], Ni₃Ti [95], Ni₂TiAl [103,105,106], Ni₃(AlTi) [107], and CoAl [108], as well as other precipitate phases [22,109,110,111]. Together, these elements substantially improve both high-temperature strength and wear resistance in Fe-based alloys. It is important to note that the NiAl phase contributes to brittleness and promotes intergranular fracture in Fe–Ni–Co–Al-based alloys [22]. To address the dual challenges of the poor room-temperature ductility and inadequate creep resistance above 600 °C shown by NiAl-strengthened ferritic steels, a thermodynamic calculation-guided alloy design approach was employed [112]. Through this method, an optimized Fe-10Cr-2Mo-11Al-13.5Ni (at. %) composition was developed and experimentally evaluated. The results demonstrate that this alloy achieves an effective balance between room-temperature ductility and HT creep performance, successfully mitigating the inherent limitations of NiAl-strengthened systems.

The development of metal materials has been marked by a significant increase in chemical complexity, driven by the need for advanced properties in demanding applications (Figure 3a) [113,114]. This diversification has led to the creation of novel materials, including medium-entropy alloys (MEAs), high-entropy alloys (HEAs), and other chemically complex systems. The strategy design of synthesizing high entropy mainly includes the regulation of the composition, morphology, structure, and surface/interface engineering (Figure 3b) [115]. The superior performance of these materials can be explained by four key effects: the high entropy effect, the sluggish diffusion effect, the lattice distortion effect, and the cocktail effect (Figure 3c) [116].

The synergistic effect also plays a critical role in high-entropy alloying approaches, where multiple principal elements are combined in near-equimolar proportions [114,117,118,119,120,121]. Among these, Al, Co, Cr, Cu, Fe, Mn, Ni, and Ti elements are the most commonly used for high-entropy alloys (HEAs) [122]. For example, the combination of Fe, Ni, Co, Cr, and Al in high-entropy configurations enhances oxidation resistance [123]. Research has demonstrated that the AlCoCrFeNi HEA containing refractory elements exhibits superior high-temperature oxidation resistance compared to traditional refractory alloys (825 Ni-based alloy and 2205 duplex stainless steel) with a similar Cr content at 1000 °C. These synergistic interactions produce a balanced combination of properties, making such alloys particularly suitable for high-temperature structural applications [124,125].

Compared to conventional high-temperature (HT) alloys, the HT properties of HEA consisting of the refractory element can be further enhanced through several mechanisms: increased anti-phase boundary energy from high alloying concentrations, restrained grain boundary sliding due to sluggish diffusion effects, and reduced recrystallization driving forces resulting from severe lattice distortion [118,120]. Furthermore, incorporating light alloy elements benefits both lightweight design [126] and plasticity optimization [120]. Beyond high-temperature performance, the multi-principal-element design also significantly improves cryogenic temperature performance [127,128,129].

Recently, iron-based high-entropy alloys (HEAs) have attracted significant attention due to their cost-effectiveness [127,130,131]. For example, Fe₅₀Mn₂₀Al₂₀Cr₅Ti₅ (Alloy 1) and Fe₅₀Mn₂₅Al₁₅Cr₅Ti₅ (Alloy 2) were identified through high-throughput CALPHAD computational screening [132]. Both alloys demonstrate excellent tensile and compressive properties at elevated temperatures, with yield strengths of 607 MPa and 643 MPa, respectively, at 700 °C. These properties result from precipitate strengthening by nano-scale L2₁ phases and stabilized fine microstructures. Similarly, a BCC-based Fe_72.4Co_13.9Cr_10.4Mn_2.7B_0.34 HEA steel achieves an exceptional balance of strength and ductility [133]. The enhanced strength originates from three synergistic mechanisms: optimized compositional modulation, refined BCC-structured grains, and the grain boundary segregation of interstitial boron. The remarkable plasticity stems from multiplanar dislocation slips, coherent interfaces, and shear band formation. This multi-element alloying strategy not only simultaneously improves strength, ductility, and oxidation resistance, but also provides a versatile platform for developing advanced materials to meet increasingly demanding high-temperature applications [134].

In summary, optimizing Fe-based HT alloys depends critically on harnessing synergistic effects among alloying elements. Through the strategic selection and combination of elements such as Cr, Ni, Al, Mo, and Ti, these alloys achieve enhanced mechanical strength, oxidation resistance, and thermal stability. These synergistic improvements are essential for developing materials capable of withstanding extreme operational conditions in demanding high-temperature applications across aerospace, energy, and manufacturing sectors.

3. Fabrication and Processing

The manufacturing methods for Fe-based HTAs include melting and casting [135], powder metallurgy (PM) [109,136], vacuum induction melting (VIM) [77,137,138,139], arc and electroslag remelting, spray deposition, laser cladding, arc welding and electro-slag welding (ESW), diffusion bonding, chemical vapor deposition (CVD), physical vapor deposition (PVD), friction stir processing [140], and additive manufacturing (AM) [141]. The choice of alloying method depends on several factors, including the desired properties of the alloy, the production scale, and the application requirements. For Fe-based HTAs, selecting the right alloying method is crucial for achieving the necessary balance of strength, oxidation resistance, and thermal stability, while also ensuring cost-effectiveness and manufacturability. These methods enable the fine-tuning of alloy properties to meet the demanding conditions of industries such as aerospace, power generation, and automotive.

Each of these methods offers distinct advantages depending on the specific application requirements and desired properties of Fe-based HTAs. Whether employing conventional melting and casting techniques or advanced processing methods such as powder metallurgy (PM) and additive manufacturing (including laser cladding and powder-bed technologies), the alloying process plays a pivotal role in developing Fe-based materials capable of withstanding extreme high-temperature conditions. The selection of processing method is ultimately determined by multiple factors including production scale, compositional complexity, and final performance specifications. While this review primarily focuses on the effects of the alloying strategy due to space constraints, it is important to acknowledge that other critical factors—including manufacturing and design approaches [142,143,144,145], machining processes [18], heat treatment protocols [146,147,148], surface treatments [149], and protective coatings [150,151]—significantly influence the ultimate properties of these materials.

Advanced high-strength steels (AHSS) constitute a specialized category of steel alloys characterized by substantially enhanced mechanical properties, with minimum yield strengths exceeding 460 MPa—markedly superior to conventional carbon steels [152]. The AHSS family comprises several distinct classifications based on microstructure and processing techniques: dual-phase (DP) steel [153], transformation-induced plasticity (TRIP) steel [154,155], press-hardened steel (PHS), twinning-induced plasticity (TWIP) steel [156], and complex-phase (CP) steel, among others [157,158]. Building upon this foundation, ultra-high-strength steels (UHSS) further push performance boundaries through sophisticated alloying strategies, incorporating multiple elements to optimize strength, ductility, and crash resistance [159,160,161]. For instance, with alloying additions of 3 wt. % and 4 wt. % Cu, a typical Fe-22Mn-0.6C TWIP steel demonstrates improved properties through a grain-refinement strategy [96]. The alloying elements are typically treated as the solution soluted in the BCC Fe phase. Lin et al. [162] showed that the introduction of alloying elements (Ni, Mo, Cr, and C) markedly amplifies the elastic modulus of Fe-based alloys by first-principles phonon calculations. And the interstitial solid solution of C provides a more significant enhancement to the elastic modulus, while Ni, Mo, Cr, and C elements notably enhance the anisotropy of the Fe-based alloy [162]. Recently, a machine learning (ML) framework was developed to predict and optimize the stretch-flangeability of AHSSs by establishing composition–microstructure–property correlations, utilizing datasets encompassing 212 steel conditions [163].

When iron-based superalloys meet additive manufacturing or 3D printing technology, it gives brings about new opportunities [92,159]. Fe-based alloys, together with Ti-based alloys, Al-based alloys, and Ni-based alloys, are the most common alloys produced via AM technology [164]. The use of 3D printing technology for Fe-based HTAs is an area of growing interest [164,165,166,167,168]. Figure 4a displays a schematic diagram of alloy design for 3D-printed metal. Optimizing alloys for metal AM involves balancing multiple factors to achieve desired mechanical properties, printability, and microstructure. The ideal AM alloy minimizes segregation and cracking (e.g., short freezing ranges), leverages rapid solidification for fine microstructures, and aligns strengthening mechanisms (precipitation, solid solution, etc.) with the characteristics of a base metal. This method allows for the production of complex geometries and custom components for HT applications [164,169].

Figure 4b presents a schematic overview of basic mechanical properties of widely used steels processed through both AM and conventional methods [169]. A comparative study of 15-5 PH stainless steel produced by additive manufacturing (direct metal laser sintering) versus traditional manufacturing (TM, wrought) revealed that AM-processed alloys exhibit superior Vickers microhardness [171]. Research on Fe-based alloys has primarily focused on steel materials [159,164], with particular emphasis on austenitic stainless steel 316L [30,142,166,172,173,174,175,176,177]. Previous studies [164,175] demonstrate that AM-produced 316L achieves a higher yield and ultimate tensile strength compared to its conventionally wrought and annealed counterparts. The enhanced yield strength and hardness are attributed to the intragranular cellular segregation network structure and randomly distributed oxide nano-inclusions formed during selective laser melting (SLM), along with the refined dendrites resulting from rapid solidification under direct metal deposition (DMD). The observed reduction in ductility can be explained by the presence of “track–track” and “layer–layer” melt pool boundaries [164].

A comparative analysis of yield strength–elongation and yield strength–impact energy relationships between 3D-printed plain carbon steels (1080 and 1040 steels) and conventional wrought steels (Figure 4c) has shown improved strength–ductility–toughness performance in the AM specimens. Notably, the 3D-printed 1080 steel achieved a yield strength of 1773 MPa, while the 1040 grade reached 1340 MPa [170]. The laser wire direct energy deposition technology has found widespread application in complex part manufacturing and welding repair applications. This technique has been successfully employed to fabricate lean duplex stainless steel 2101 using underwater laser wire direct energy deposition [178].

AM technology has received extensive attention for use in materials functionalization. For example, complex-shaped Nd₂Fe₁₄B magnets [179] and Fe-based soft magnetic materials [180] have been successfully fabricated using the SLM process. The AM-processed Fe-based soft magnetic materials exhibit superior magnetic properties compared to those of the samples produced by traditional molding techniques [180]. Functional gradient Fe-based alloys can be readily manufactured via the AM process [142], as the process follows a layer-by-layer stacking principle [181]. The AM technology enables the precise fabrication of porous or lightweight Fe-based alloy structures, further optimizing their functional applications in biological materials [182,183], energy-absorbing materials [181,184], catalytic supports [24,185], shape memory alloys [184], and other specialized applications [167,181].

The steel industry is a major contributor to global carbon emissions, driving the need for sustainable and eco-friendly fabrication and processing methods for Fe-based alloys [186]. Sustainability-related research topics in iron and steel production have been thoroughly summarized by Raabe [186]. Recent advances focus on reducing energy consumption, minimizing waste, and utilizing renewable resources while maintaining material performance. The transition toward the sustainable manufacturing of Fe-based alloys demands innovative approaches to reduce environmental impacts while maintaining material performance. A promising direction is hydrogen-based direct reduction (H-DRI) [187,188], which replaces carbon-intensive coke with green hydrogen as the reducing agent for iron ore. A sustainable method, turning oxides directly into green alloys in bulk forms through a one-step solid-state process, was reported by Wei et al. [189]. Further, sustainable bulk nano-structured porous alloys were produced via the reactive vapor-phase dealloying–alloying synthesis route by same group [190]. Complementing this shift in primary production, electric arc furnaces (EAFs) powered by renewable energy are enabling the large-scale recycling of steel scrap with significantly lower carbon footprints [186,191,192]. When combined with alloy designs that avoid hazardous or difficult-to-recycle elements, this approach supports a circular economy model for Fe-based materials [193]. The processing stage also offers sustainability gains through advanced techniques like additive manufacturing [194], which minimizes material waste through near-net-shape fabrication, and solid-state methods such as friction stir welding [140] that eliminate energy-intensive melting steps. Atypical ferroalloys, e.g., rare earth element permanent magnets (NdFeB), are widely used in a multitude of industries, especially in electric motors for electric and hybrid vehicles and wind turbines [195]. The recycling potential of NdFeB permanent magnets and the identified physical and metallurgical separation and recovery technologies have been attracting more and more attention [196,197].

Further improvements have emerged from strategic alloy development, whereby critical raw materials like cobalt and rare earth elements are substituted with more abundant alternatives. For instance, new generations of maraging steels have achieved high strength without relying on Co or Mo [198]. A sustainable ultra-high-strength maraging steel (Fe₁₈Mn₃Ti), with the abundant Mn as a major alloying element, was obtained through controlled solute segregation and α-Mn nanoprecipitation [198]. Concurrently, digital tools like machine learning optimize energy use in rolling and heat treatment processes [71,199], while lifecycle assessments guide material selection based on comprehensive environmental metrics.

Recently, artificial intelligence and machine learning (AI/ML) have been used in material discovery and design [200,201,202,203]. AI/ML are transforming iron-based alloy design by enabling the rapid exploration of vast compositional and processing spaces, reducing trial and error, and uncovering novel materials [2,44,68,177,204,205,206,207,208]. An ML framework for designing high-performance multi-principal element alloys (Fe-Cr-Ni-Al/Ti) is shown in Figure 5 [97]. The process follows four key steps: data preparation (collecting composition–property datasets), feature selection (choosing input variables), model selection (picking an ML algorithm), and model application (using the model to predict optimal compositions). Two distinct training strategies are highlighted: the C-strategy, which directly uses alloy compositions as model inputs, and the P-strategy, which relies on composition-derived features (e.g., thermodynamic or structural descriptors). The study demonstrates how this ML-driven approach efficiently identifies promising alloys, focusing on optimizing strength and toughness, and bypassing traditional trial-and-error methods [97]. As datasets grow and algorithms improve, AI/ML will play an even greater role in optimizing process conditions [71], predicting mechanical properties [209,210,211], and designing the next generation of advanced steels [2], high-entropy alloys [8,212], functional iron-based materials [213], and others [72].

4. High-Temperature Properties

The high-temperature (HT) properties of Fe-based alloys are critical for applications in aerospace, power generation, chemical processing, and other industries where materials are exposed to extreme conditions. Research on Fe-based alloys and steels has predominantly focused on chemical corrosion [214,215,216], biological corrosion [217,218], and performance in complex environments [214,219,220]. When subjected to elevated temperatures, Fe-based alloys exhibit a range of essential performance characteristics, including oxidation and corrosion resistance, mechanical strength, creep resistance, thermal stability, and microstructural stability. These properties collectively determine their suitability to demanding high-temperature applications.

4.1. Oxidation and Corrosion Resistance

Fe-based alloys, particularly austenitic stainless steels (types 304, 316, and 347), have served as nuclear fuel cladding materials since 1951 [85]. The alloying strategy significantly influences the oxidation and corrosion resistance of these metals. Protective oxide layers such as Cr₂O₃ [221], Al₂O₃ [222,223] and FeCr₂O₄ [52] form on the alloy surface, effectively preventing degradation in both oxidizing and carburizing environments. Previous investigations [51,221,224,225] have demonstrated that adding Cr to form an Fe–Cr alloy enhances oxidation resistance at elevated temperatures. Additional elements including Al [54,222,226], Ni [59,84], Co [227], Zr [60], Mn [228], and others [229] have been employed to further improve HT oxidation and corrosion resistance performance. Building upon the Fe–Cr alloy foundation, subsequent developments incorporated new alloying elements such as Ni [224], Al [50], Y [50], Ti [47,146], Si [47], and Mo [230]. In recent years, FeCrAl alloys have emerged as particularly outstanding due to their exceptional HT resistance properties.

The development status for three typical accident-tolerant fuel cladding materials (coated Zr-based cladding, FeCrAl cladding, and SiC/SiC cladding) was thoroughly summarized in a previous review [85]. A comparative analysis of FeCrAl alloy corrosion behavior in a light water reactor (LWR) coolant environments is presented in Figure 6A(a,c). During normal operation and anticipated operational occurrences (including both hydrogen water chemistry (HWC) and normal water chemistry (NWC)), protective Cr-rich oxide films dominate after one year of exposure. In contrast, accident scenarios involving HT steam oxidation (Figure 6A(c)) primarily yield alumina-based protective layers. Figure 6B exhibits optical micrographs of oxidized HEAs with various compositions (HEA06 = Al_0.5CrFeNiMn, HEA06 = Al_0.5CrFeNiCo, HEA08 = Al_0.5CrFeNiCo + Zr, HEA08 = Al_0.5CrFeNiCo + Y). The HEA08 samples consistently formed compact, smooth oxide layers without macroscopic exfoliation, while other HEA alloys exhibited varying degrees of oxide particle spallation after HT oxidation. These results unequivocally demonstrate the critical role of alloy design in determining HT isothermal oxidation performance [85].

Under irradiation, Fe-based nuclear materials undergo progressive degradation as atomic displacements generate defects that evolve into clusters and voids, while transmutation-produced helium and hydrogen exacerbate damage [231]. These effects cause radiation hardening, swelling, and segregation—all thermally accelerated—ultimately compromising mechanical performance [232,233,234,235,236]. Current research focuses on radiation-tolerant designs including nanostructured alloys [232,237], ODS steels [238,239], and HEAs [235,236,240,241,242] that engineer microstructures to control defect accumulation. Cheng et al. [240] and Tan et al. [241] systematically evaluated the irradiation responses of HEAs, highlighting their unique potential utility in nuclear environments. The chemical complexity and lattice distortion inherent to HEAs promote enhanced defect recombination, suppressing void swelling and radiation-induced hardening compared to conventional alloys. While their unique properties offer potential radiation resistance, significant gaps remain between laboratory results and practical implementation. The field needs rigorous studies that simultaneously address fundamental radiation behavior, engineering challenges, and economic feasibility to determine if HEAs can evolve from scientific novelties to viable nuclear materials [242].

Figure 6C gives the mechanism diagram of the surface steam oxidation of FeCrAl alloys [87]. The study has revealed that Al₂O₃ formation plays the dominant role during HT steam oxidation between 1000 °C and 1300 °C. Cr also has a positive impact on surface-oxidizing film formation [49], particularly by enhancing long-term oxidation resistance through reduced oxidation weight gain rates. FeCrAl alloys have garnered considerable attention for use in nuclear fuel cladding applications due to their superior HT oxidation resistance compared to conventional zircaloy [23,27,92]. Further comparative studies under actual operating conditions (500–520 °C for 6–12 months in a loop seal region of an 85 MW_th waste-fired CFB boiler in Sweden) showed that FeCrAl alloys outperform both austenitic stainless steels and Ni-based alloys in terms of oxidation resistance [94]. Beyond experimental investigations, HT corrosion behaviors have been successfully simulated using the Calphad (Calculation of Phase Diagrams) approach [243].

Hybrid molecular dynamics (MD) and Monte Carlo (MC) simulation serve as an effective tool for investigating elemental migration dynamics behavior. To compare diffusion coefficients among three alloys (FeCrAl, NiCoCrAl, and AlCoCrFeNi HEA) at 1100 °C [244], hybrid MD/MC simulations were conducted using the large-scale atomic/molecular massively parallel simulator package. Figure 6D demonstrates the simulation results of the Al-depletion layer for FeCrAl alloy (Figure 6D(a,b)), NiCoCrAl alloy (Figure 6D(c,d)), and AlCoCrFeNi HEA (Figure 6D(e,f)) at 1100 °C. The HEA system, exhibiting the highest configurational entropy, demonstrates maximum atomic chaos, followed by NiCoCrAl and the FeCrAl alloy system (Figure 6D(a,c,e)). The increasing rate of mean square displacement (MSD) of the different elements reflects their diffusion rates (Figure 6D(b,d,f)). The Al diffusion coefficients follow the order FeCrAl > NiCoCrAl > HEA system. The significantly lower diffusion coefficient (approximately one order of magnitude) in AlCoCrFeNi HEA indicates that inward oxygen diffusion dominates Al₂O₃ scale growth. This inward oxygen diffusion promotes the formation of columnar Al₂O₃ grain structures, while reduced outward Al diffusion decreases oxidation rates and inhibits interface rumpling, thereby enhancing oxidation resistance [244].

To further improve HT performance, minor elements including Mo [61], Y [77], Nb [245], Ta [246], Si [84], and so on [23,91,238] have been introduced into the FeCrAl alloy. Recent advances have employed multi-component [247] and high-entropy designs [248,249], along with strategies like oxide dispersion strengthening (ODS) [238,250], machine learning [2,251], and optimized machining processes [251,252]. Beyond HT steam environments, the influences of alloying elements on FeCrAl(Si)/(FeCrNi) alloys in corrosive environments containing KCl (or K₂CO₃) + HCl (600 °C, 168 h) were also investigated by atom probe tomography [84]. This further confirmed that alloying elements benefit corrosion protection through the formation of inward-growing heterogeneous scales.

The corrosion behavior of Fe-based alloys in various molten salt environments has been extensively investigated, with studies on Li₂CO₃-Na₂CO₃-K₂CO₃ with TP347H stainless steel at 650 °C [253], solar salt (60%NaNO₃-40%KNO₃) with ferritic steels at 400–600 °C [254], chloride salt (NaCl–KCl) with 316L stainless steel at 800 °C [255], and Li₂CO₃–Na₂CO₃–K₂CO₃ and LiCl–Li₂O with Fe–36Ni alloy at 650 °C [256]. A comprehensive study of molten carbonate corrosion behavior in TP347H stainless steels with varying Al contents (0–2.5 wt. %) revealed significant performance differences [253]. The steel without Al content (0 wt. % Al) exhibited severe corrosion, demonstrating a weight gain of approximately 9.44 mg/cm² after 1000 h exposure, corresponding to a corrosion rate of 103.07 µm/year. In contrast, the 2.5 wt. % Al alloy showed optimal performance with the lowest weight gain (~6.0 mg/cm²) and corrosion rate (75.09 µm/year).

Figure 6. (A) Various protective films ((a,b) Cr-rich spinel or hematite films, (c) Al₂O₃ film) formed on the surfaces of FeCrAl alloys in various environments: (a,b) in low- and high-oxygen-activity aqueous environments, (c) under HT steam oxidation (1200 °C, 4 h), Reprinted with permission from Ref. [85] Copyright © 2018 Elsevier. (B) Surface morphology of the HEA alloys after the isothermal oxidation test for 20 h, Reprinted with permission from Ref. [257] Copyright © 2021 Elsevier. (C) Schematic illustration of the surface steam oxidation mechanism in an Fe–Cr–Al alloy, Reprinted with permission from Ref. [87]. Copyright © 2022 Elsevier (D) Hybrid molecular dynamics and Monte Carlo simulations of atomic migration behavior in the Al-depletion layer for FeCrAl alloy (a,b), NiCoCrAl alloy (c,d), and AlCoCrFeNi HEA (e,f) at 1100 °C, Reprinted with permission from Ref. [244] Copyright © 2022 Elsevier.

Figure 6. (A) Various protective films ((a,b) Cr-rich spinel or hematite films, (c) Al₂O₃ film) formed on the surfaces of FeCrAl alloys in various environments: (a,b) in low- and high-oxygen-activity aqueous environments, (c) under HT steam oxidation (1200 °C, 4 h), Reprinted with permission from Ref. [85] Copyright © 2018 Elsevier. (B) Surface morphology of the HEA alloys after the isothermal oxidation test for 20 h, Reprinted with permission from Ref. [257] Copyright © 2021 Elsevier. (C) Schematic illustration of the surface steam oxidation mechanism in an Fe–Cr–Al alloy, Reprinted with permission from Ref. [87]. Copyright © 2022 Elsevier (D) Hybrid molecular dynamics and Monte Carlo simulations of atomic migration behavior in the Al-depletion layer for FeCrAl alloy (a,b), NiCoCrAl alloy (c,d), and AlCoCrFeNi HEA (e,f) at 1100 °C, Reprinted with permission from Ref. [244] Copyright © 2022 Elsevier.

Figure 7A(a,b) [253] shows a mechanistic diagram of molten carbonate corrosion for Al-modified TP347H steel. In the initial corrosion stage (Figure 7A(a)), the alloy surface undergoes simultaneous reactions with molten carbonate and atmospheric oxygen, forming iron, chromium, and aluminum oxides. These oxides subsequently react with the carbonate melt to generate lithium ferrite (LiFeO₂) and lithium chromite (LiCrO₂), along with various spinel phases. Al plays a pivotal role by facilitating the development of a continuous, compact LiFeO₂ layer that shields the substrate from direct exposure to the corrosive medium. As corrosion processes to the stable stage (Figure 7A(b)), ongoing oxygen diffusion promotes the formation of a protective inner oxide layer primarily composed of Cr₂O₃ and Al₂O₃, with NiO contributing to the protective barrier. This composite inner layer demonstrates exceptional stability in the molten carbonate environment, significantly enhancing long-term corrosion resistance. The Al–Cr synergy is particularly significant, as Al not only accelerates initial LiFeO₂ formation, but also improves the density and adhesion of the subsequent Cr₂O₃-rich layer. The proposed mechanism (Figure 7A(a,b)) demonstrates that a higher Al content accelerates the development of the protective LiFeO₂–LiCrO₂ outer layer, while the Cr-dependent inner oxide layer provides durable protection. This dual-layer system—comprising an outer lithium-containing oxide layer and an inner chromia–alumina-rich barrier—collectively delivers superior corrosion performance in high-temperature molten carbonate environments. These findings highlight the critical importance of optimizing Al concentration to achieve both rapid initial protection and sustained corrosion resistance [253].

4.2. Mechanical Properties

The HT mechanical properties of Fe-based alloys (such as carbon steels, stainless steels [258], and other iron-based superalloys [259]) are crucial for elevated-temperature applications. These properties are fundamentally governed by composition, microstructure, and processing [17]. For 15Cr–22Ni–1Nb austenitic heat-resistant steels, the HT ultimate tensile strength (UTS = 346–361 MPa at 650 °C) is 30–40% lower than at room temperature, though appropriate heat treatment can significantly improve elongation after fracture [260]. In FeCrNiAl alloys, the addition of vanadium (0–12 wt. %) introduces coherent hierarchical precipitates (nano-scale Fe₂₃Zr₆ phases within B2–NiAl precipitates), enhancing HT yield strength from 210 MPa (0 V) to 401 MPa (12 V). The HT compressive strain of these ferritic alloys also increases with V content, attributable to the dynamic recrystallization (DRX) behavior [104]. A study of four Fe-based HEAs (Fe₃₆Mn₂₁Cr₁₈Ni₁₅Al₁₀-Alloy1, Fe₃₆Co₂₁Cr₁₈Ni₁₅Al₁₀-Alloy 2, Fe₃₅Mn₂₀Cr₁₇Ni₁₂Al₁₂Ti₄-Alloy 3, and Fe₃₅Co₂₀Cr₁₇Ni₁₂Al₁₂Ti₄-Alloy 4) [261] at room temperature (RT), 400 °C, 600 °C, and 800 °C revealed distinct mechanical responses. The face-centered cubic (FCC) structured Alloy 2 exhibited the lowest yield strength values at both RM (250 MPa) and HT (150 MPa). In contrast, Alloy 4, featuring a body-centered cubic (BCC) matrix with plate-like L2₁ (ordered FCC) precipitates, demonstrated superior strength characteristics, with 1420 MPa at RM and 795 MPa at 600 °C [261].

HT torsion tests (800–1200 °C) conducted at high strain rates on Fe-based alloys revealed that plastic deformation is governed by a dislocation climb mechanism, providing insights for hot formability studies [262]. Complementary research on Aermet100 steel through isothermal hot compression tests (800–1100 °C) demonstrated that the HT deformation behavior can be accurately predicted using artificial neural network modeling [263]. Zhang et al. [258] investigated the mechanical properties of 316 stainless steels under combined neutron radiation (11.8 dpa) and elevated temperature (320 °C) conditions using in situ X-ray diffraction and ex situ electron microscopy techniques. The study revealed that irradiated specimens exhibited significantly higher yield stresses and reduced total elongations compared to unirradiated controls at both 23 °C and 320 °C.

Xu et al. [264] systematically investigated the hardness, HT softening resistance, and wear performance (Figure 8a–c) of a multicomponent Fe₅₀Mn₂₅Al₁₅Cr₅Ti₅ alloy. The Fe-based alloy demonstrated superior performance compared to Hadfield steel (40Mn18Cr3), exhibiting higher hardness, enhanced resistance to HT softening, and improved wear resistance [264]. At 800 °C, the wear mechanism was attributed to the formation of a dense, protective oxide film on the surface (Figure 8d). Remarkably, Fe-based high-entropy alloys with a composition of Fe-20Mn-15Cr-10V-10Al-2.5C (at.%) achieved Vickers hardness values up to 520 HV [265]. This exceptional hardness originates from localized elemental concentration variations and atomic-scale crystal lattice disorder. The characteristic high-entropy effects—including entropy stabilization, sluggish diffusion, lattice distortion, and cocktail effects—promote the formation of simple solid solution phases instead of complex intermetallic compounds [114]. This optimized multicomponent alloying strategy not only enhances strength, ductility, and oxidation resistance, but also establishes a versatile platform for developing advanced materials to meet growing demands in HT applications.

Four distinct Fe-based alloy systems (austenitic stainless steel, ingot metallurgy M2 tool steel, a complex FeCrCNbMoWB alloy with fine microstructure, and a hypereutectic FeCrCMoNb alloy with coarse microstructure) were investigated for their HT wear resistance using single impact tests [75], continuous impact abrasion tests, and erosion tests [266]. Both RT and HT (600 °C) single impact tests and oblique erosion tests demonstrated strong correlations with material hardness. During continuous impact abrasion testing, the complex FeCrCNbMoWB alloy exhibited superior wear resistance compared to other materials at both RT and 600 °C [75,266]. Recent work by Singla et al. [267] comprehensively reviewed the effects of various alloying elements (B, C, Cr, Mn, Mo, Nb, Si, Ti, V, and rare earth metals) on the wear resistance performance of Fe-based alloys.

The performance of HTAs depends not only on their composition, but also on their long-term degradation resistance. While ferroalloys generally exhibit poor creep resistance above 600 °C, the incorporation of solid-solution strengthening elements such as W, Mo, and Nb enhances their resistance to deformation under prolonged HT stress. Strategic alloying can effectively improve these high-temperature creep properties. For instance, carbon-free FeNiAlCr alloys demonstrate excellent creep-resistant above 600 °C [268]. The addition of aluminum (Al) to TP347H stainless steel substantially improves both strength and elongation at 650 °C compared to the base alloy [253]. Ti additions (0, 2, 4 and 6 wt. %) notably enhance the FeNiAlCrMo alloy, and particularly creep resistance at 700 °C under stresses ranging from 70 to 300 MPa [269]. Subsequent investigations by the same research group examined the effects of minor hafnium (Hf) additions (0.5 wt. %) on FeNiAlCrTi ferritic superalloy [269,270], revealing that creep resistance depends critically on three factors—the volume fraction of precipitates, the lattice misfit between precipitates and matrix, and precipitate coarsening kinetics. Extensive correlation analyses together with ML models were used to predict the creep of HT alloys as well [206]. Oxide dispersion strengthening (ODS) with Y₂O₃ dramatically improves the creep resistance of FeCrAl alloys at 1100–1300 °C [271]. The HT creep resistance properties of FeCrAl were significantly improved at 1100–1300 °C. Furthermore, high-throughput design approaches have successfully developed low-activation, high-strength creep-resistant steels for nuclear reactor applications at 650 °C [272].

Additive manufacturing (AM) offers distinct advantages to HT performance compared to conventional manufacturing methods [167]. In the case of 15-5 PH stainless steel [171], AM-produced specimens exhibit superior mechanical properties to their wrought (WST) counterparts, including higher yield strength (790 MPa vs. 610 MPa) and ultimate tensile strength (830 MPa vs. 620 MPa) at 593 °C under a strain rate of 10⁻³s⁻¹. Except for the Vickers microhardness [171], the 15-5 PH stainless steel produced by AM showed a higher yield strength (790 MPa) and ultimate tensile strength (830 MPa) than wrought stainless steel (WST, 610 and 620 MPa) at a temperature of 593 °C and a strain rate of 10⁻³s⁻¹, despite showing slightly lower ductility. Creep rupture testing at 593 °C under 211 MPa revealed that AM steel outperforms WST material [171], with longer rupture times (157.2 h vs. 121.2 h) and significantly lower minimum creep rates (0.0003%/h vs. 0.038%/h), demonstrating superior creep resistance. Selective laser melting (SLM) has enabled the development of 316L stainless steel with enhanced strength characteristics, achieving a room temperature yield strength of 598.2 MPa and HT yield strength of approximately 350 MPa at 600 °C [273]. These mechanical properties can be further improved through micro- and nano-scale TiC [273] or TiB₂ additions [274]. Notably, incorporating 10 vol% TiB₂ nanoparticles produces exceptional strength values, reaching 980.9 MPa at RM and remaining at 833.8 MPa at 600 °C, 702.4 MPa at 700 °C, 401.9 MPa at 800 °C, and 95.8 MPa at 1000 °C [274].

5. Applications

Modern high-temperature material systems include superalloys [1,2], refractory metals [275], ceramics [10,276], and composites [277], each offering unique advantages for extreme environments [278,279]. Material selection requires balancing mechanical performance, environmental stability, and cost. While Ni/Co superalloys dominate ultra-high temperature applications, Fe-based alloys remain crucial for moderate temperatures (500–750 °C) due to their cost-effectiveness and manufacturability. Advanced variants like ODS, HEA, and HSS steels are expanding their capabilities. These alloys continue serving critical roles in power generation, petrochemical, and automotive applications, where economics outweigh the need for extreme performance. Ongoing material innovations ensure their continued relevance in high-temperature engineering.

Iron and iron-based alloys have long been recognized as promising anode materials due to their favorable electrochemical properties and cost-effectiveness [280,281,282]. Recent advancements have revealed particularly promising results for iron-based oxygen-evolution electrodes, where an in situ-formed lithium ferrite (LiFe₅O₈) surface layer develops during operation [256]. A dense oxide film composed of lithium ferrite (Figure 7B(b)) is formed on the Fe-36Ni electrode after pre-oxidation (100 mA/cm² at 650 °C) (Figure 7B(a–c)). Clearly, a nickel-rich transition layer can be observed between the oxide layer and the bulk metal by electron probe X-ray microanalyzer (EPMA) mapping (Figure 7B(d)), which is attribute to the different diffusion rates of Fe and Ni. And the protective layer plays an important role in HT oxidation resistance and mechanic stability [256]. The HT oxygen evolution reaction performance of the pre-oxidized Fe–36Ni electrode was assessed in molten LiCl–Li₂O for 20 days, and the calculated consumption rate was only approximately 0.04 cm/year. This dual functionality, which uniquely combines inherent material stability with catalytic enhancement, presents a transformative strategy for developing cost-effective, Earth-abundant electrode materials capable of withstanding prolonged operation in high-temperature electrochemical systems.

Hydrogen embrittlement (HE) is a widely known phenomenon that occurs in various high-strength materials such as high-strength steels, high-Mn steel, Al-based alloys, Ti and Ti alloys, and Mg-based alloys, etc. [283,284,285,286]. HE has detrimental effects in many industrial sectors, such as in municipal wastewater environments [286], the energy sector [287] and hydrogen in transport [288]. The growing demand for metallic materials resistant to both environmental corrosion and HE under HT presents a significant challenge [289]. And both alloy elements and material microstructure modification have a significant impact on the HE of steels [283,290]. It was discovered, for example, that the retarded HE of Fe–Mn–C TWIP (twinning-induced plasticity) steels improves as the Cu element percentage rises [291]. Al addition is an effective solution to improving the HE resistance of high-Mn austenitic steels [292]. Furthermore, multi-principal element design can also improve the hydrogen embrittlement resistance, which has been well summarized by Li et al. [293]. High-strength steels are particularly susceptible to gaseous hydrogen embrittlement (GHE) [294,295]. Neuharth and Cavalli [296] investigated the high-temperature hydrogen embrittlement effect on four types of austenitic stainless steels (310S, 316/316L, and 321). They showed that both the burst strength and the ductility were reduced by exposure to hydrogen at 3.45 MPa and 800 °C for four hours. A small percentage of refractory elements (Mo, Nb, W) can improve the high-temperature (800 °C) resistance to HE in steels and alloys through intermetallic hardening, which retards phase transformations during testing [289].

Amorphous alloys, also known as metallic glasses, are a class of materials that lack long-range atomic order, unlike crystalline materials [297]. Due to their disordered atomic configurations, they exhibit unique physical and chemical properties that differ significantly from those of conventional crystalline alloys [43,297,298]. One of the most attractive features of amorphous alloys is their wide compositional flexibility, which allows for the fine-tuning of their properties [26,299,300]. Alloying elements such as B, P, Si, and C are commonly used to improve the glass-forming ability and tailor the properties of the alloy [26,204]. High-performance Fe-based nanocrystalline alloys have also received widespread attention, especially for use in electrical and electronic devices with good soft-magnetic performance [26,300,301,302]. Good mechanical [303] and high-temperature properties [300,304,305] can be obtained as well.

Magnetic alloys have been developed for elevated-temperature applications. Alloying [26,299,306,307,308,309] and heat treatment [300,310,311] play an important role in the development of soft magnetic properties. A previous work [305] indicated that the additions of Co and Ni elements to Nanoperm-type Fe₈₈Zr₇B₄Cu₁ soft magnetic alloys dramatically increase the Curie temperature (from 67 to 289 °C) of the intergranular amorphous phase. And low coercivities less than 30 Am⁻¹ can be maintained for Fe₇₇Co_5.5N_i5.5Zr₇B₄Cu₁ nanocrystalline alloys over the temperature range from 50 to 500 °C. The addition of Co and Ni also enhanced the magnetization at different temperatures (25–650 °C) [305]. The high thermal stability of Fe-based nanocrystalline alloys was achieved via the isothermal annealing (420 °C, 0–96 min) of amorphous precursors [300]. When the annealing time is greater than 4 min, the first exothermic peak, ascribed to α-Fe crystallization, disappears (Figure 9A(a)). The disappearance of the first exothermic peak indicates that the precipitation of α-Fe grains levels to a plateau value. A “dual phase co-growth” mechanism has been proposed to understand the kinetics of nano-grain growth (Figure 9A(b)). Further, atom probe tomography (APT) was used to analyze the sample (420 °C, 48 min) so as to predict the grain growth during isothermal annealing. As can be seen in Figure 9B(a,b), typical chemical segregation was observed. The regions with high Fe concentration exhibit a granular shape with an average size of about 20 nm, which is attributed to the α-Fe-like grain, and Si is dissolved in a-Fe like grains. Cu clusters are distributed around the Fe-rich grains with sizes of 2–4 nm, while the metalloid elements (B, P, and C) seemingly play an interphase shielding role in the a-Fe like grains (Figure 9B(c)). The number densities of α-Fe like grains (~2 × 10²³) and Cu clusters (~1.2 × 10²⁴) were respectively estimated from the elemental maps (Figure 9B(d,e)). The formation of nano-sized grains (~20 nm) out of the amorphous matrix gives rise to a synergetic increase in saturation magnetization (B_s = 1.84 T), magnetic permeability (μe = ~25,000) and hardness (H = ~15 GPa), with high thermal stability (Figure 9A(a)) [300].

Fe-based alloys can be used as catalytic supports [24,312] and catalysts [313,314]. Typically, amorphous Fe-based alloys or metallic glasses have been used in functional applications as heterogeneous catalysts (e.g., FeSiB for H₂O₂ [45], peroxymonosulfate (PMS) [315], and peracetic acid [316] catalytic degradation, FeMoSiB [317] and (Fe_73.5Si_13.5B₉Nb₃Cu₁)_91.5Ni_8.5 [318] for decolorization). Similarly, the alloying strategy [215,319] and heat treatment [317] have a great influence on the catalytic performance. The stability (chemical stability [298,316], thermal stability) of the alloy is also required in catalyst or catalyst-support applications. A previous review [24] summarized that the FeCrAl alloys can be used as an exceptional catalyst support, especially when used in highly exothermic and endothermic reactions within aggressive chemical environments (>700 °C). The main structures used as catalyst support are in turn monolith, foams, and fibers (Figure 9C), and all are suitable for use in fixed-bed reactors that are easily recycled. The FeCrAl catalyst support can be used in industrial burners, automotive tail gas converters, H₂ and syngas production, and other applications [24].

Recent work by Magnier and colleagues [313] has demonstrated the development of a highly active and cost-effective oxygen evolution reaction (OER) catalyst for alkaline media. Their study revealed that Fe–Ni alloy substrates spontaneously develop an active surface layer of NiFe oxo-hydroxide species after ageing and activations, which serves as the catalytically active phase. This in situ formation of surface-active sites presents a promising approach for designing efficient OER electrocatalysts, as it combines the stability of alloy substrates with the high-activity characteristic of transition metal oxo-hydroxides. It was found that the NiFe oxo-hydroxide surface layer was determined by the alloying elements and initial atomic Fe/Ni ratio, thus driving the oxygen evolution reaction [313]. The spontaneous surface restructuring phenomenon observed in this system offers new insights into catalyst design strategies that leverage dynamic surface transformations under operational conditions to achieve optimal catalytic performance.

Simultaneously, Fe-based alloys themselves can be used as catalysts. Melt-spun FeSiB glassy ribbons have shown good catalytic reactivity in wastewater remediation [45,315,316]. The amorphous Fe-based alloys were produced by vacuum melt-spinning in a Ti-gettered Ar atmosphere (Figure 9D). the PMS activation mechanism can be explained by the disordered atomic packing structure, which provides catalytically active sites, as well as amorphous zero-valent iron as both the electron donator and the acceptor (Figure 9D) [315]. Further, the inclusion of Si and B could improve the glass-forming ability and surface stability.

In short, Fe-based alloys offer a balance of cost, manufacturability, and performance at high temperatures. Their properties can be tailored via alloy design (Cr, Ni, Mo, and Al, etc.), processing innovation (AM), microstructural engineering (precipitates, grain control), and coating treatment. For ultra-high temperatures (>1000 °C), Ni/Co superalloys or ceramics may be required, but advanced Fe-based alloys (e.g., ODS, high-entropy alloys) continue to push boundaries. Further, the Fe-based alloys play a crucial role across various fields [17,21,22,23,24,25,26,27,28,29], due to their strength, corrosion resistance, and functional properties. In structural and mechanical applications, they are essential in construction, automotive, and aerospace industries, offering durability and toughness. Their high-temperature resistance makes them suitable for use in gas turbines, jet engines, and power plant components. Furthermore, the addition of alloying elements is intended not only to improve their high-temperature properties, but also to endow them with or enhance their functional applications, such as in the functional gradient Fe-based alloy [142], biodegradable Fe-based alloys [25,320], antibacterial alloy [321], Fe-based shape memory alloy [11], iron-based superconducting alloy [322,323], iron-based magnetic alloy (amorphous alloys [44], atypical Nd₂Fe₁₄B magnet [324,325], and others [326]), etc. [313,327,328].

Figure 9. (A,a) DSC curves for the Fe_84.75Si₂B₉P₃C_0.5Cu_0.75 alloy before (as-quenched) and after annealing at 420 °C for different times (1–96 min). (A,b) Average grain size (symbols represent the experimental data from XRD and lines are the proposed modeling curves, while the inset is the proposed “dual phase co-growth model”) of the Fe-based nanocrystalline alloys during isothermal annealing at 420 and 460 °C. (B,a,b) APT elemental maps (60 × 60 × 110 nm) of the Fe-based nanocrystalline alloy after annealing at 420 °C for 48 min. (c) Concentration depth profile from the selected area (3 × 3 × 60 nm) in (B,a). (B,d,e) Fe and Cu, respectively, delineated by 90 at.% and 4 at.% iso-concentration surfaces, Reprinted with permission from Ref. [300] Copyright © 2019 Elsevier. (C) Three typical structures (monolith, foam, and fiber) of FeCrAl alloys as catalytic supports, Reprinted with permission from Ref. [24] Copyright © 2020 American Chemical Society. (D) Schematic illustration of the preparation and proposed PMS activation mechanism of FeSiB amorphous alloys for dye degradation, Reprinted with permission from Ref. [315] Copyright © 2017 Elsevier.

Figure 9. (A,a) DSC curves for the Fe_84.75Si₂B₉P₃C_0.5Cu_0.75 alloy before (as-quenched) and after annealing at 420 °C for different times (1–96 min). (A,b) Average grain size (symbols represent the experimental data from XRD and lines are the proposed modeling curves, while the inset is the proposed “dual phase co-growth model”) of the Fe-based nanocrystalline alloys during isothermal annealing at 420 and 460 °C. (B,a,b) APT elemental maps (60 × 60 × 110 nm) of the Fe-based nanocrystalline alloy after annealing at 420 °C for 48 min. (c) Concentration depth profile from the selected area (3 × 3 × 60 nm) in (B,a). (B,d,e) Fe and Cu, respectively, delineated by 90 at.% and 4 at.% iso-concentration surfaces, Reprinted with permission from Ref. [300] Copyright © 2019 Elsevier. (C) Three typical structures (monolith, foam, and fiber) of FeCrAl alloys as catalytic supports, Reprinted with permission from Ref. [24] Copyright © 2020 American Chemical Society. (D) Schematic illustration of the preparation and proposed PMS activation mechanism of FeSiB amorphous alloys for dye degradation, Reprinted with permission from Ref. [315] Copyright © 2017 Elsevier.

6. Conclusions and Prospect

Fe-based high-temperature alloys have emerged as a vital materials class, offering an optimal balance of mechanical properties, thermal stability, oxidation resistance, and cost efficiency. While they may not match the peak performance of nickel-based superalloys in the most extreme conditions, their adaptable properties and economic advantages have secured their position across diverse industrial applications. Recent breakthroughs in alloy design, processing methods, and surface treatments are continuously pushing the boundaries of their high-temperature capabilities, opening new avenues for performance enhancement and application-specific optimization.

The field is currently witnessing transformative developments through several key approaches. Advanced alloying strategies, particularly those incorporating high-entropy alloy concepts, are creating new compositional spaces with enhanced properties. Simultaneously, the development of nanostructured and nanoprecipitate-strengthened variants is addressing longstanding challenges in creep resistance and oxidation performance. Modern manufacturing technologies, especially additive manufacturing, are revolutionizing component production by enabling complex geometries with precisely controlled microstructures. Perhaps most significantly, the integration of artificial intelligence and machine learning is accelerating every aspect of materials development, from initial discovery through performance prediction to process optimization.

However, several critical challenges must be overcome to fully realize this potential. Technical hurdles such as additive manufacturing defects, the high costs associated with some advanced alloys, and the need for sustainable production methods remain significant barriers. The implementation of AI/ML approaches faces its own challenges, including data limitations and interpretability issues. Looking ahead, the most promising opportunities lie at the intersection of these technologies—where computational design, nanoscale engineering, and advanced manufacturing converge. This synergistic approach promises to unlock new generations of Fe-based alloys capable of meeting the demands of tomorrow’s most challenging applications, from next-generation power systems to hypersonic platforms.

This review provides a comprehensive examination of contemporary developments in Fe-based high-temperature alloys, focusing on three critical aspects: innovative alloy design strategies, advanced processing techniques, and their resulting high-temperature performance characteristics. By synthesizing current knowledge and identifying future directions, it aims to provide both a reference for materials researchers and a roadmap for continued advancement in this essential field.