Eutectic alloys are a class of multi-phase materials named for their formation through eutectic reactions during solidification. They have a long history as the most widely used casting alloys. High-entropy alloys (HEAs), on the other hand, are a novel class of multi-principal element alloys that have rapidly developed since their conceptualization in 2004. Combining the advantages of eutectic alloys and HEAs, eutectic high-entropy alloys (EHEAs) were first proposed in 2014. Over a decade, EHEAs have been systematically investigated by focusing on alloy design, microstructure/performance optimization, large-scale fabrication, and potential applications. Their unique microstructures and excellent comprehensive properties have made EHEAs promising materials across various domains, garnering significant attention in recent years. By revisiting the advances in composition design, manufacturing, and applications of EHEAs over the past decade, this review offered insights into future trends and developments in this rapidly evolving field.

Vacuum arc remelting (VAR) is the principal remelting process for producing high-quality Ti-based alloy and Ni-based superalloy ingots with high density, fine chemical homogeneity, and minimal defects. Numerical modeling plays a crucial role in understanding the mechanisms and dynamics of various phenomena occurring at different scales during the VAR process. It also aids in optimizing operational parameters. In this paper, the development of multiscale simulations for VAR ingot solidification over the last two decades is introduced. The following four aspects are addressed: numerical models at various scales, macroscopic transport phenomena, microstructure and defect evolution, and the effects of process control parameters on the VAR ingot quality. Furthermore, the current limitations in this field and proposed future development directions are discussed.

Recently, the rapid advancement of extreme non-equilibrium material processing and fabrication techniques, such as 3D printing and rapid die-casting, has led to the continuous development of new materials with exceptional properties. However, current non-equilibrium processing technologies face technical challenges, such as the lack of clear guidelines for process optimization, which considerably limits the advancement and application of advanced materials. The solidification and solid phase transformations involved in materials prepared through non-equilibrium processing pertain to a non-equilibrium dissipative system and manifest throughout the entire dynamic process of material fabrication. By investigating key scientific issues such as non-equilibrium phase transformation dynamics, non-equilibrium solute diffusion, and solute-drag effects, developing a theoretical framework for the entire non-equilibrium material processing, from solidification to solid phase transformation is possible. This not only provides theoretical support for the design and fabrication of non-equilibrium materials but also introduces novel concepts for optimizing process parameters in non-equilibrium processing technologies. This review is crucial for advancing non-equilibrium phase transformation theory and deepening our understanding of fundamental theoretical research. Interfaces play a critical role in microstructure control during material processing, thereby making an accurate theoretical description of their kinetics is especially important. This review focuses on the common characteristics of liquid/solid interfaces during melting, solid/liquid interfaces during solidification, and solid/solid interfaces during solid state phase transformations and summarizes and analyzes the history and current state of sharp-interface models for interface kinetics. Using the solidification of binary alloys as an example, the review first introduces interface kinetic theories under local non-equilibrium conditions, covering descriptions of interface kinetic processes and interface kinetic models for steady-state and non-steady-state conditions. The physical nature of one-step and two-step trans-interface diffusion is demonstrated. Next, the review describes interface kinetic theories under full non-equilibrium conditions by comparing the applications of the kinetic energy method and the effective mobility method for non-equilibrium solute diffusion in bulk phases. Thereafter, it introduces interface kinetic theories incorporating the partial solute drag effect present and discusses limitations in current methods for addressing partial solute drag. This study aims to enhance understanding of interface kinetics, offering insights into microstructure control. Finally, an outlook on the future of non-equilibrium interface kinetic theories is provided, which outlines directions for future research.

Allvac 718Plus is a newly developed nickel-based superalloy derived from Inconel 718 alloy via composition optimization. Its maximum service temperature is approximately 55 ^oC higher than that of Inconel 718. With its excellent combination of creep resistance, fatigue resistance, machinability, and weldability, the Allvac 718Plus is highly suitable for manufacturing high-temperature components that can operate at up to 700 ^oC. As a precipitation-strengthened superalloy that is relatively new with limited application history, understanding the evolution of its secondary phases during heat treatment is crucial for optimizing its properties via microstructure control. In this context, the secondary phases found in Allvac 718Plus are introduced, including the primary strengthening γ′ phase, the main grain-boundary η phase, and the γ″, δ, σ, and C14 Laves phases that form under specific conditions. The precipitation behaviors of the γ′ and η phases during standard heat treatments are examined, along with the effects of presolidification and direct aging treatments. Additionally, the evolution of secondary phases during prolonged thermal exposure are explored. The results demonstrate that the formation of a more stable composite γ″-γ′ structure is a promising strategy to achieve long-term serviceability for the alloy. The influence of the microstructural evolution of secondary phases during high-temperature service on fatigue and creep resistance is also analyzed, focusing on the roles of the two primary secondary phases. Furthermore, this paper highlights the correlation between the sluggish kinetics of γ′ phase precipitation in Allvac 718Plus and its weldability. A comprehensive overview of the harmful effects of the Laves and η phases on cracking during welding and strain-age cracking is also provided.

Refractory high-entropy alloys (RHEAs) have emerged as an innovative and promising class of high-entropy alloys that are primarily composed of multiple refractory elements, such as Ta, Nb, Mo, W, and Hf. These elements confer to the RHEAs with exceptional mechanical properties at high temperature, including excellent strength and stability. In addition to their desirable high-temperature performance, RHEAs also exhibit remarkable resistance to oxidation, wear, corrosion, and radiation. These resistance characteristics grant them potential as application materials in extreme environments, such as aerospace, nuclear reactors, and high-performance industrial machinery. As application materials, RHEAs have attracted evergrowing attention as the candidate materials to replace the traditional nickel-based superalloys due to their single solid solution phases and excellent stability in terms of structure and performance. Although they are promising, RHEAs fabricated using traditional methods, such as casting and powder metallurgy, present several shortcomings that limit their widespread application. It is often difficult to achieve a uniform composition in RHEAs that are prepared by conventional arc melting, which results in significant elemental segregation. Additionally, the size of the ingots prepared by this way is restricted to a small, button-like scale due to the limitations of the casting molds. These drawbacks significantly restrict the development, customization, and application of RHEAs in various industries, underscoring the need for advanced manufacturing techniques that can overcome these restrictions. Laser additive manufacturing (LAM) has emerged as a transformative approach to addressing the abovementioned challenges. By utilizing a high-energy density laser beam as a heat source, LAM enables a “discrete-stacking” or layer-by-layer forming process that can be precisely controlled through computer-aided design. This process offers exceptional flexibility in the manufacture of complex shapes, the fine-tuning of alloy composition, and the achievement of a uniform microstructure, thereby minimizing problems such as elemental segregation. Additionally, laser cladding (LC), which is a subset of LAM, provides the ability to deposit coatings that demonstrate superior mechanical and chemical properties to the surface of substrates, which further expands the application potential of RHEAs. This study presents a comprehensive review of current research on the LC of RHEAs while focusing on the unique microstructures and properties of RHEA coatings (RHEACs). It delves into the influences of alloy composition and processing parameters on the phase composition, microstructure, microhardness, as well as abrasion, oxidation, and corrosion resistances of RHEACs. Furthermore, this review discusses the evolution of RHEAC microstructure during the LC process and how it affects the performance of the coatings. Lastly, this review summarizes the current state of research on LC-RHEAs and outlines future development trends. It also highlights key challenges such as optimizing processing parameters, improving coating-substrate bonding, and tailoring microstructures for enhanced performance to guide future research studies and industrial applications.

Incorporating metastable austenite is the one of the key strategies for achieving synergistic improvement in the strength and ductility of high-strength steels. Through in situ deformation-induced martensitic transformation during tensile loading, metastable austenite can delay necking while enhancing work-hardening capacity. Concurrently, ultrahigh-strength steel components are facing increasing demands in terms of lightweightness and service in complex environments; hence, they will be required to have a higher fracture toughness without compromising strength. Research has focused on incorporating the tougher austenite phase in high-strength steels to improve their fracture toughness and preserve ductility. Metastable austenite contributes to enhanced fracture toughness through transformation toughening and its interactions with cracks, which can deflect or blunt cracks. However, freshly formed martensite, a product of martensitic transformation, can reduce the toughening effect or even deteriorate fracture toughness due to its inherent brittleness and effect on the local stress state. This paper reviews recent research progress on the relationship between metastable austenite and fracture toughness of high-strength steels, examining the toughening and embrittlement mechanisms of the phase. In addition, it outlines future design principles for metastable austenite incorporation in high-strength steels to achieve synergistic improvements in strength and toughness.

Owing to their high thermal stability, good high-temperature mechanical properties, and excellent high-temperature oxidation resistance, refractory high-entropy alloys (RHEAs) are strong candidates for structural materials in high-temperature applications. To reduce the density and improve the high-temperature oxidation resistance of RHEAs, in this study, the Al element was added into CrNbTiV alloys, forming a series of CrNbTiVAl _x RHEAs (x = 0.25, 0.5, 0.75, 1.0). The effects of Al content on the microstructure, mechanical properties, and high-temperature oxidation behaviors of the CrNbTiV RHEAs were studied using XRD, SEM, EDS, and an electronic universal testing machine. A mixture of bcc, Laves, and α-Ti phases was found in the CrNbTiVAl _x RHEAs and equiaxed grains were observed in the bcc phase. Increasing the Al content decreased the density of the alloys and reduced the yield strength from 2037 to 1371 MPa. The specific yield strength ranged from 215.93 MPa·cm³/g in CrNbTiVAl_0.75 to 323.33 MPa·cm³/g in CrNbTiVAl_0.25. After oxidation at 900 ^oC, the CrNbTiVAl _x RHEAs exhibited parabolic oxidation kinetics and their high-temperature oxidation resistance was improved due to increased Al content. The oxidized products were determined as Al₂O₃, (CrNbTiVAl)O₂, and VO _x. The surfaces of the alloys with low Al content formed a continuous and compact complex oxide (CrNbTiVAl)O₂ that effectively prevented the diffusion of O₂ into the substrate. Increasing the Al content decreased the amount of complex oxide (CrNbTiVAl)O₂, forming denser, continuous, and finer Al₂O₃ oxides on the surface that appreciably improved the high-temperature oxidation resistance.

M-B (M = Fe, Co, Ni) alloys have garnered significant attention in the automotive, petrochemical, and power electronics industries owing to their excellent corrosion resistance, wear resistance, and high-temperature strength. The service performances of the M-B alloys are closely related to that of borides. Among them, M₂₃B₆ generally exists as a metastable phase. However, the understanding of its formation is limited compared to that of other borides. To reveal the effect of Fe/Co content ratio on the solidification behavior of the Fe-Co-B alloys, particularly the formation of M₂₃B₆ phase, alloys with nominal composition of (Fe_{1 - x} Co _x)_79.3B_20.7 (x = 0-1) were undercooled using the melt fluxing technique. Consequently, the solidification behaviors were systematically investigated. With the increase in the Co content, the stable eutectic reaction changed from L→α-M + M₂B for x <0.4 to L→α-M + M₃B for x >0.4. Consequently, the two eutectic reactions occurred at the same temperature at x =0.4, and a peritectic reaction L + M₂B→M₃B was observed at x > 0.4. With the increase in the undercooling, the primary phase changes from M₂B and M₂₃B₆ to α-M/M₃B in the alloys with x ≤0.6, and from M₃B, M₂B, and M₂₃B₆ to α-M/M₃B in the alloys with x >0.6. The increase in Co content reduced the critical undercooling for the M₂₃B₆ phase to precipitate primarily and improved its stability, that is, the primary M₂₃B₆ phase decomposed into α-M/M₂B in the following cooling process when the Co content is not excessively high. However, it could sometimes be reserved to room temperature in case of a very large Co content.

The evolution of the microstructure during solidification and solid-state phase transformation is crucial for controlling the material microstructure and optimizing performance. Achieving an integrated numerical simulation of the microstructural evolution from solidification to solid-state phase transformation is a cutting-edge challenge in material-microstructure simulation. This study focuses on Au-Pt alloys, utilizing a multiphase field model combined with a microstructural information transfer algorithm to simulate and predict microstructural evolution during the solidification and solid-state phase transformation under different initial composition conditions. The study successfully realizes an integrated simulation prediction of the microstructural evolution across both processes, revealing the influence of microsegregation and grain boundaries during solidification on subsequent processes of decomposition and spinodal decomposition.

Silicon (Si)-containing aluminum (Al) alloys are highly valued in the fabrication of large-scale components with thin walls and complex geometries, such as automobile engine housings, gas turbine blades, and electrical equipment housings. These alloys are favored owing to their high fluidity, excellent filling ability, low risk of hot cracking, and excellent weldability. However, the broad solidification range of these alloys can lead to the formation of coarse primary Al dendrites and casting defects such as shrinkage porosity. To improve casting quality, inoculation is commonly carried out in practice. Numerous inoculants, such as Al-Ti, Al-B, Al-Ti-B, Al-Ti-C, and Al-Ti-B-C, have so far been developed. Among these, Al-Ti-B is widely adopted in industry owing to its high grain refinement efficiency. However, its efficiency decreases significantly when the Si content in Al alloys exceeds 5% (mass fraction), a phenomenon known as “Si poisoning”. To this end, an Al-Nb-B inoculant was developed to replace Al-Ti-B. Al-Nb-B demonstrates excellent grain refinement effect and effective resistance to Si poisoning, making it ideal for cast Al alloys with high Si contents. Typically, Al-Nb-B is fabricated using conventional casting methods with Al-Nb and Al-B intermetallic alloys as feedstocks. However, because these feedstocks have higher melting points than Al alloys, the reaction time required for the fabrication of Al-Nb-B is lengthy. This leads to the coarsening and sedimentation of nuclei in the molten Al, resulting in a non-uniform distribution in the as-cast inoculant, limiting its industrial application. To overcome this challenge, a fabrication method utilizing molten salt reactions has been proposed to homogenize the distribution of nuclei in Al-Nb-B inoculants. This approach not only improves the homogeneity of the nuclei but also reduces their average particle size from 10 μm to 1 μm. This is attributed to the relatively fast reaction rate between the molten salt and the liquid Al. As a result, the grain refinement efficiency improved significantly from 34% to 79%. Furthermore, plastic deformation aids in further homogenizing nucleus distribution. Hot extrusion is more effective than cold-rolling in this regard, showing the best results for enhancing grain refinement and antidegradation performance of the molten salt-based inoculant. The performance of this newly developed molten salt-based inoculant was verified during the fabrication of cast Al alloys ZL104 and ZL114A, which not only refines grain size by 79.2% and 78.5%, respectively but also significantly reduces casting defects. Consequently, the ductility and impact toughness of both ZL104 and ZL114A alloys improved simultaneously. This study provides a new approach to fabricating high-performance Al-Nb-B inoculants for cast Al alloys.

The electropulse-assisted forming process has been widely used in various plastic deformation applications owing to its advantages in improving formability and refining microstructure. However, the influence of electropulse on the dynamic extrusion deformation process remains unclear. In this study, the effects of electropulse on dynamic precipitation and microstructure evolution of AZ91 magnesium alloy during extrusion were investigated using electropulse-assisted extrusion (EPAE) technology. The results demonstrate that under critical deformation conditions for complete dynamic recrystallization, the EPAE process reduces the volume fraction of the β-Mg₁₇Al₁₂ phase, promotes its spheroidization, and enhances both the average grain size and the maximum basal texture intensity. These effects become more pronounced with increasing peak current density. Specifically, with a peak current density of 6.4 × 10⁷ A/m² during the EPAE process, the volume fraction of the β-Mg₁₇Al₁₂ phase decreased from 76.9% to 16.5%, the average grain size increased from 1.07 μm to 3.54 μm, and the maximum basal texture intensity increased from 3.39 to 5.92, compared to conventional hot extrusion. The bimodal structure observed in the EPAE-processed AZ91 alloy was attributed to the pinning effect caused by the inhomogeneous distribution of the β-Mg₁₇Al₁₂ phase. Experimental and theoretical analyses indicated that the increase of Gibbs free energy variation and atomic diffusion flux during extrusion of AZ91 alloy caused by the combined thermal and athermal effects of the pulsed current was the main reason for the experimental phenomena, which promoting the solution of β-Mg₁₇Al₁₂ phase and uniform distribution of Al solute atoms nearby while also increasing the grain boundary migration rate. Moreover, the electropulse strengthened the basal texture in β-Mg₁₇Al₁₂ particle-depleted regions by accelerating basal <a> slip.

Eutectic high-entropy alloys show excellent properties, such as casting property, mechanical properties, corrosion resistance properties, and so on. They are usually consisted of two kinds of phases, which would be compete with each other in the non-equilibrium solidification process. Fe₇(CoNiMn)₈₀B₁₃ eutectic high-entropy alloy has complex phase transition and microstructure evolution behavior during the non-equilibrium solidification process. In order to reveal the non-equilibrium solidification characteristics and microstructure evolution mechanism, Fe₇(CoNiMn)₈₀B₁₃ eutectic high-entropy alloy was undercooled by the molten glass fluxing method in this work. The results show that the solidification path and microstructure of undercooled Fe₇(CoNiMn)₈₀B₁₃ eutectic high-entropy alloy can be divided into 5 categories. At low undercooling (ΔT < 57 K), the cooling curve has only one recalescence phenomenon. The corresponding solidification microstructure is primary B-rich phase + peritectic α-(Fe, Co, Ni, Mn) phase + eutectic structure. At medium undercooling (ΔT = 57~111 K), there are two recalescence phenomena on the cooling curve. The corresponding solidification microstructure can be divided into two types: the first is primary M₂₃B₆ dendrite + secondary α-(Fe, Co, Ni, Mn) halo + regular eutectic; the second is primary α-(Fe, Co, Ni, Mn) dendrite + regular eutectic. At high undercooling (ΔT = 139~198 K), the cooling curve shows a single recalescence phenomenon again. The corresponding solidification microstructure can be divided into two types: the first is a mixture of B-rich phase + M₂₃B₆ + α-(Fe, Co, Ni, Mn) three phases, and the second is M₂₃B₆ + α-(Fe, Co, Ni, Mn) anomalous eutectic. Note that the type of primary phase transited for twice with the increase of undercooling: B-rich phase→M₂₃B₆ phase→α-(Fe, Co, Ni, Mn) phase. In addition, the orientation relationship of two eutectic phases in regular eutectic at low undercooling is consistent with that of two phases in anomalous eutectic at high undercooling.

The development of high-temperature creep-resistant Al alloys is essential for manufacturing aerospace and transportation equipment. Conventional creep-resistant Al alloys have several limitations, including high costs, complex heat treatment processes, and challenging processing requirements. Selective laser melting (SLM) technology enables the fabrication of metal materials with ultrafine microstructures and high concentrations of strengthening phases due to its rapid cooling rates, substantial temperature gradients, and unique thermal cycling. This capability provides a promising path for the development of next-generation creep-resistant Al alloys. In this study, a novel Al-9Si-3Fe-2Mn-Ni (mass fraction, %) alloy using the SLM technique was developed. This Al-Si alloy was engineered by controlling the diffusion of slow-diffusing elements and intermetallic compounds (IMCs) that strengthen the material. The high-temperature creep behavior of this alloy was evaluated through uniaxial tensile creep experiments conducted at varying deformation temperatures (300-400 ^oC) and applied stresses (33-132 MPa). The experimental results demonstrate that the alloy exhibits good creep performance under the experimental conditions. The stress exponent ranged from 6.4 to 13.6, showing a decreasing trend with increasing temperature. The creep deformation mechanism is known as dislocation creep. Below 350 ^oC, the continuous Al-Si eutectic network reduces the overall stress via load transfer, with IMCs strengthening the alloy via the Orowan mechanism. At 400 ^oC, the Al-Si eutectic structure fractures and dissolves, with the IMCs and dispersed Si phases providing the primary strengthening mechanism. Increased applied stress amplifies the dislocation slip systems within the alloy, intensifying the interactions between dislocations and precipitates, leading to destabilization and deformation and ultimately reducing creep life.

The multi-dimensional, multi-scale forming characteristics of laser powder bed fusion (LPBF) 3D printing technology, combined with its complex non-equilibrium solidification process, result in multilayered microstructures that differ significantly from those produced by traditional manufacturing methods. However, it is challenging to apply existing heat treatment solutions, developed for conventional manufacturing processes, to LPBF. Therefore, a tailored heat treatment approach is required for LPBF-printed components to regulate their microstructure and properties effectively. This study investigated the modulation mechanism of subsequent heat treatment on the non-equilibrium microstructure and high-temperature mechanical properties of 3D-printed GH4099 superalloy produced via LPBF. The findings reveal that solution treatment influences the recrystallization behavior of the printed microstructure and the precipitation behavior of carbides and γ' phases, which play critical roles in determining the alloy's high-temperature elongation. The multi-scale heterogeneous structure in the LPBF-fabricated GH4099 alloy enhances its microstructural thermal stability beyond that of conventional castings and forgings. Consequently, a high solution heat treatment temperature is necessary to achieve complete recrystallization. Following solution treatment at 1150 ^oC for 1.5 h, the columnar grains in the GH4099 prints were transformed into equiaxed grains, and large size twins were formed. Additionally, the precipitation of M₂₃C₆ carbides at the grain boundaries was suppressed. During subsequent aging heat treatment, the recrystallization induced by the solution treatment mitigated the distortion energy stored in the 3D-printed grains, thereby suppressing γ' phase precipitation in the matrix. As a result, by optimizing the heat treatment process, a favorable balance between high-temperature strength and plasticity was achieved in the GH4099 alloy.

Alumina-forming austenitic (AFA) steel is expected to be applied to high-temperature components of ultra-supercritical thermal power plants. However, the high-temperature strength and stability of AFA steel need to be improved further. Here, the influence of pre-aging on the precipitation behavior, microstructural evolution, and mechanical properties of cold-rolled AFA steel was investigated. The results showed that pre-aging significantly influences the synergistic strengthening due to dislocations and precipitation in cold-rolled AFA steel during the process of high-temperature aging treatment. The precipitates in a sample that received pre-aging treatment exhibited strong pinning effect on grain boundaries and dislocations, which enhances the effect of precipitation strengthening by boosting the number of nucleation sites and the driving force for the formation of the precipitates. Compared to cold rolling with a 10% thickness reduction but without pre-aging, the formation of the Laves phase and the B2-NiAl phase after pre-aging for 24 h resulted in increased pinning on the dislocations and grain boundaries, which prevented dislocation slip, generated stress concentrations, boosted the number of nucleation sites and the driving force for the formation of the precipitates, and accelerated the phase-transition process; the volume fraction of the precipitates also increased significantly. Hardness and tensile tests at room temperature showed that the strength and hardness resulting from both cold rolling and cold rolling after pre-aging first increased and subsequently decreased.

Eutectic high-entropy alloys (EHEAs) have exhibited excellent mechanical properties. However, their rapid solidification behaviors during additive manufacturing processes still require further investigation. In the present study, Ni_43.5Co₁₉Cr₁₀Fe₁₀Al₁₅Ti₂Mo_0.5 EHEA via copper mold casting and selective laser melting (SLM) were produced to study the influence of solidification conditions, such as cooling rate, on the phase area fraction, phase composition, grain morphology, and mechanical properties of the alloy. SEM, EBSD, TEM, and tensile testing were used to systematically analyze the solidification behaviors and mechanical properties of this EHEA. The center of the as-cast specimen has the lowest cooling rate, a large amount of fcc primary phase appears and forms equiaxed crystals, with a B2 phase area fraction of 16.9%. As the cooling rate increases, the amount of fcc primary phase decreases, and the area fraction of the B2 phase increases to 23.0% on the surface of the as-cast specimen. Meanwhile, the concentration of Al in the B2 phase of each region in the as-cast specimen is 23.2% (atomic fraction, the same below). However, with the continuous increase in the cooling rate, the area fraction of B2 phase tends to reach its lowest value in the SLM specimen, with only 15.8% in edge-on orientation, and the concentration of Al in the B2 phase decreases to 16.5%. The decrease in the area fraction of the B2 phase in SLM samples is due to solute trapping caused by the high cooling rate, resulting in the formation of a supersaturated solid solution and a reduction in the amount of liquid phase available for forming eutecticphase. In addition, during the SLM process, a high scanning rate results in a large temperature gradient, which promotes the formation of columnar crystals. Reducing the scanning rate to 500 mm/s causes a columnar-to-equiaxed transition due to the decrease in temperature gradient. The mechanical properties of the SLM specimens are superior to those of the as-cast specimens, with a room-temperature ultimate tensile strength of (1320.5 ± 4.5) MPa and a fracture elongation of (25.8 ± 2.2)%.