Aluminum (Al) alloys, a typical lightweight material, are limited to applications at temperatures below about 200 ^oC. The high-temperature range of 300-400 ^oC has been a longstanding bottleneck for traditional Al alloys. In this study, the underlying mechanisms of this service bottleneck are first discussed, and key scientific solutions aimed at overcoming the bottleneck are proposed. A new microstructure designing strategy is proposed to develop advanced heat-resistant Al alloys through phase transformation that couples rapidly diffusing solute atoms with slowly diffusing ones. This strategy leads to three design approaches for thermal stability: (1) interfacial solute segregation at the nanoprecipitate/matrix interfaces, (2) interstitial solute ordering within the coherent nanoprecipitates, and (3) multiple interfacial coherency coupling with multiscale microstructural features. By manipulating the microalloying effect at the atomic length scale, a series of 300-400 ^oC heat-resistant Al alloys were developed. Furthermore, the potential development directions of the heat-resistant Al alloys are also explored as possible references for future work.

Tungsten material is an industrially important material owing to its high density, high melting point, excellent hardness, and wear resistance. Crystal defects (e.g., dislocations and vacancies) are common in its structure, thereby influencing the performance of tungsten materials. Therefore, controlling these defects is crucial for enhancing their performance. A deep understanding of how defects form and evolve serves as a theoretical basis for controlling them. This article reviews the mechanisms of defect formation and research advancements in tungsten materials from two key perspectives: defect introduction during the sintering process and through stress effects. Accordingly, this study explores defects in tungsten materials from the viewpoint of preparation and processing, summarizing recent advancements and prospects in related fields, aiming to provide a valuable reference for future research on tungsten materials.

With the rise of data-driven methods as the fourth scientific paradigm, their impact on the third paradigm—physical model-driven approaches—has been significant in the field of alloy design. However, neither paradigm can overcome the trade-off between model accuracy and interpretability, particularly in mechanical performance design. As a consequence, they fail to meet the efficiency and rationality requirements necessary for alloy development within Material Genome Engineering, especially for metal structural materials. This challenge has led to the emergence of the fifth paradigm, AI4Sci, in alloy design. This article provides an overview of various cases employing the physical metallurgy-guided artificial intelligence method system. It systematically explains how to integrate physical models and mechanisms with artificial intelligence at three levels: numerical data guidance, image data guidance, and mechanism guidance. This approach aims to resolve the inherent trade-off between accuracy and interpretability in alloy design. In addition, it explores the theoretical foundations, advantages, and limitations of three paradigms—multi-scale physical models, artificial intelligence, and AI4Sci—within the field. For cross-scale modeling and materials science large models, this article offers insights into conceptual frameworks and technical methodologies for the future development of each scientific paradigm in alloy design.

Monel K-500 alloy is a Ni-based alloy that is widely used in marine environments and chemical industries because of its exceptional corrosion resistance and mechanical properties. The synergetic modulation of directional solidification and thermal processing (DS-TP) technique combines DS and in situ heat treatment in a single experiment, thus eliminating the influence of environmental changes and avoiding aging effect. To investigate the effect of the DS-TP technique on the mechanical properties of the alloy, samples were prepared using DS alone and the DS-TP technique at different growth rates. Subsequently, the microstructures and mechanical properties of the samples were analyzed. In the DS experiments, an Al₂O₃ ceramic crucible (diameter: 10 mm) containing the alloy sample was heated using a graphite heater and an electromagnetic induction coil. As the sample was superheated to 200 K, it was immersed in the Ga-In-Sn liquid at a certain pulling rate. In the DS-TP experiments, the directionally solidified sample was in situ annealed at 1223 K for 1 h and then immersed into the liquid. Subsequently, the sample was subjected to an aging process at 923 K for 5 h. The microstructure of the directionally solidified Monel K-500 alloy showed columnar γ grains with pronounced <001> texture. When the growth rate decreased, the temperature gradient at the solid-liquid interface during directional solidification increased. Lower growth rates led to a coarser microstructure, lesser microsegregation of Cu, and fewer transverse grain boundaries. As the growth rate decreased from 100 μm/s to 5 μm/s, the yield strength, tensile strength, and elongation increased from 248 MPa, 421 MPa, and 63.4% to 288 MPa, 487 MPa, and 69.9%, respectively. Unlike the case of the directionally solidified alloys, the nanoscale γʹ hardening phase precipitated in the DS-TP-treated alloys and the degree of microsegregation decreased. Further, the yield strength and tensile strength increased from 368 and 640 MPa, respectively, to 386 and 686 MPa, respectively, as the growth rate decreased from 100 μm/s to 5 μm/s. The distribution of intergranular cracks in the fractography was similar to that of large-angle grain boundaries in the region closing the fracture. With the growth rate decreasing, intragranular cracks gradually appeared, and the number of intergranular cracks decreased. Moreover, grain deviation from the preferred growth orientation increased the dislocation density and decreased the elongation. Grain refinement promoted the homogeneous distribution of dislocations and caused a slight increase in the elongation. At a growth rate of 5 μm/s, the tensile strength and yield strength of the DS-TP-treated alloy increased by 34% and 41%, respectively.

Bulk metallic glasses (BMGs) have unique microstructures that result in excellent physical and chemical properties. In this study, the impact of replacing Cu with Ag on the glass-forming ability (GFA), crystallization kinetics, mechanical properties, and corrosion resistance of the Zr₅₅Ti₃Cu_{32 - x} Al₁₀Ag _x (x = 0, 1, 1.5, 2, and 2.5; atomic fraction, %) BMGs in the Zr-Ti-Cu-Al alloy system was examined, aiming to develop new Ni/Be-free BMGs for biomedical applications. XRD and DSC analyses demonstrate that replacing Cu with appropriate amounts of Ag improves the GFA of the alloy system and considerably increases the crystallization activation energy (E_g, E_x, E_p1, and E_p2), thereby enhancing thermal stability. From a thermodynamic perspective, Ag has a large negative heat of mixing with other elements. Furthermore, the addition of Ag enhances the interaction among components and promotes chemical short-range ordering in liquid, which can improve the local filling efficiency and inhibit the long-range diffusion of atoms, thereby improving the GFA. At the atomic level, Ag exhibits a considerable atomic radius disparity with the primary constituents, and its inclusion can generate a proficient and localized stacking configuration, thereby achieving reduced internal energy and augmented viscosity and enhancing the GFA of Zr₅₅Ti₃Cu_{32 - x} Al₁₀Ag _x BMG. Mechanical property tests showed that the fracture strength increased with the increase of Ag content. In addition, the compressive deformation ability of Zr₅₅Ti₃Cu_{32 - x}Al₁₀Ag _x BMGs is improved by the addition of appropriate Ag. The compressive strain of the new Zr₅₅Ti₃Cu_30.5Al₁₀Ag_1.5 reaches 5.49%, which is 120% higher compared to the initial system. The addition of Ag may create local heterogeneity in the microstructure, allowing many secondary shear bands to appear during the expansion of the primary shear band, which increases the plasticity of the BMG. Electrochemical corrosion behavior analysis showed that the addition of appropriate Ag reduced the corrosion current density and increased the self-corrosion potential of Zr₅₅Ti₃Cu_{32 - x} Al₁₀Ag _x BMG. Moreover, Ag enhanced the biocorrosion resistance of Zr₅₅Ti₃Cu_{32 - x} Al₁₀Ag _x BMG in simulated body fluid and phosphate-buffered saline. Therefore, the new Zr-Ti-Cu-Al-Ag BMG system has shown great application potential as a biomedical material.

Hf or Ta is widely added to powder metallurgy (PM) Ni-based superalloys to improve their microstructure and mechanical properties. However, research on the mechanism by which Hf and Ta synergistically affect creep performance is lacking. In this study, the effect of Hf and Ta on the creep rupture characteristics and properties of PM Ni-based superalloys at a temperature range of 650-750 ^oC was studied at multiple scales using SEM, EBSD, and TEM. The results showed that Hf and Ta significantly prolonged the creep rupture time, reduced the minimum creep rate, and improved the operating temperature and creep strength. The types of fracture morphologies at various creep temperatures were consistent, the crack source area exhibited intergranular fracture, the crack propagation area exhibited mixed fracture, but the addition of Hf and Ta significantly reduced the fraction of the crack source area. Considering that the stacking fault energy increased with increasing creep temperature, the creep deformation mechanism changed from microtwin shearing at 650 ^oC to microtwin and superlattice stacking fault shearing at 750 ^oC. In addition, Hf and Ta increased the content of MC-type carbides, significantly reducing the density of annealing twin boundaries and effectively inhibiting the nucleation of secondary cracks. Hf and Ta refined the M₂₃C₆ phase on grain boundaries and discontinued its precipitation, thereby strengthening the grain boundary and inhibiting the intergranular fracture. Hf and Ta reduced the stacking fault energy at various creep temperatures and increased the density of deformed microtwins, thereby increasing the resistance to dislocation movement. Moreover, Hf and Ta increased the volume fraction and average size of the secondary γ′ phase and increased the lattice mismatch between the γ and γ′ phases, thereby enhancing the strengthening effect of the γ/γ′ phase interface.

The 16MnCrS5 gear steel, known for its exceptional machinability and hardenability, is commonly utilized in the production of gears and worms in the automotive industry. However, the quenching process of this steel tends to provoke deformation, leading to increased wear and an inability of gear teeth to mesh. This issue seriously restricts the broader use of 16MnCrS5 gear steel. This study explores the quenching deformation of 16MnCrS5 gear steel through a combination of experimental research and numerical simulation to provide theoretical insight to mitigate this deformation in industrial production. The quenching deformations of C-notch samples derived from 16MnCrS5 gear steel, varying in grain size, banded structures, and hardenabilities were first measured. Subsequently, employing the deform finite element analysis software, the temperature field, stress field, and phase field during the quenching of these samples were simulated, thereby visually portraying the corresponding quenching deformation processes. The results indicate that the quenching deformation of 16MnCrS5 gear steel escalates with an increase in grain size and the proportion of banded structures. For instance, the sample with a grain size of 75 μm demonstrated nearly double the quenching deformation of the sample with a grain size of 22 μm. Moreover, when the grade of the banded structure surpasses 3, the quenching deformation of the sample markedly increases. Concurrently, the results revealed a positive correlation between quenching deformation and hardenability of 16MnCrS5 gear steel. Specifically, when the hardness at 9 mm from the quenching end (J9) > 32.2 HRC, the sample's core is largely martensitic, showing a stronger correlation with hardenability. Conversely, when J9 ≤ 32.2 HRC, there is noticeable bainitic transformation in the sample's core, resulting in a weaker correlation between the quenching deformation and hardenability. The experimental research and numerical simulations suggest that the intrinsic mechanism of quenching deformation in 16MnCrS5 gear steel is mainly attributable to thermal stress and martensitic transformation-induced stress. Notably, the temporal and spatial inhomogeneity of the martensite transformation in time and spatial distribution is the predominant factor affecting the quenching deformation of 16MnCrS5 gear steel.

The transformation-induced plasticity (TRIP) effect considerably enhances the material properties of TRIP-assisted duplex steel due to the martensitic transformation. However, as martensitic transformation progresses, a complex microstructure forms from the intermixing of three phases (i.e., austenite, ferrite, and martensite) in the steel, which results in complex damage behavior, crack nucleation, and propagation characteristics. In this study, under engineering strain up to 55%, TRIP-assisted duplex stainless steel Fe-19.6Cr-2Ni-2.9Mn-1.6Si was characterized to investigate microcrack characteristics. Herein, different types of microcracks were statistically categorized using SEM. Additionally, microcrack nucleation and propagation laws were analyzed in light of microscopic features characterized by EBSD, including phase distribution and grain and phase boundaries. The results show that the majority of microcracks are situated at the phase boundary between original austenite and ferrite, constituting about 70% of all microcracks. The number of microcracks located at the ferrite grain boundary accounts for about 20% of the total, while the number of microcracks located at the original austenite grain boundary accounts for only about 10% of the total. The interface between martensite and ferrite emerged as the primary site for microcrack nucleation. Furthermore, the study identifies three distinct microcrack nucleation sites influenced by various boundary types: at the intersection of martensite, ferrite, and austenite phases; at the junction of martensite/ferrite phase boundary and ferrite grain boundary; and at the cross point of martensite/ferrite phase boundary and the original austenite grain boundary. Therefore, microcracks might propagate along the original austenite/ferrite phase boundary or ferrite grain boundary with a smaller angle (< 30°) to the phase boundary. In addition, microcracks are less apt to propagate along the austenite grain boundary.

High-temperature furnace rolls are subjected to extreme conditions, including high temperatures and heavy loads, rendering them susceptible to oxidation, wear, and other forms of failure. To address these issues, this study investigates the preparation and properties of CoNiCrAlY-ZrB₂ composite powders and coatings. CoNiCrAlY serves as the metal matrix, and ZrB₂ acts as the ceramic reinforcement phase. Two variants of CoNiCrAlY-20%ZrB₂ (mass fraction) composite powders were fabricated using one-step and step-fashion mechanical alloying (MA) techniques (marked by MA-1 and MA-2, respectively). The microstructure and phase composition of the coatings were studied using SEM, XRD, and TEM. Mechanical properties were also investigated. High-temperature friction and wear tests were conducted at 550-950 ^oC. Results indicate that the particle size of the composite powder decreases with increasing MA time. Step-fashion MA successfully produced ZrB₂-reinforced CoNiCrAlY composite powder, with ZrB₂ particles evenly distributed throughout the CoNiCrAlY matrix. When alloyed for 35 h, the average particle size (D₅₀ = 38.6 μm) met the specifications for high-velocity oxygen-fuel (HVOF) spraying. CoNiCrAlY-20%ZrB₂ composite coatings were then prepared via HVOF spraying. Coatings derived from MA-2 powders exhibited higher melting states, denser microstructures, and lower porosity (0.28%) compared to those made with MA-1 powders. These coatings also displayed superior hardness (738 HV_0.3) and fracture toughness (5.21 MPa·m^1/2). High-temperature wear resistance was tested for both MA-1 and MA-2 composite coatings. At 950 ^oC, a protective glazing layer of Al₂O₃, Cr₂O₃, and CoCr₂O₄ was formed on the surface of the composite coatings. The coatings demonstrated effective self-lubrication at 750 ^oC due to the formation of the “glazing layer”. Above 750 ^oC, the MA-2 composite coating outperformed the one-step coating in wear resistance. Specifically, at 950 ^oC, the wear rate of the MA-2 composite coating was 1.71 × 10^-14 m³·N^-1·m^-1, considerably lower than that of the MA-1 composite coating (4.28 × 10^-14 m³·N^-1·m^-1). In conclusion, the addition of ZrB₂ nanoparticles to the CoNiCrAlY coating considerably enhanced its friction and wear properties at high temperatures. The step-fashion mechanical alloying method demonstrated superior coating density, hardness, and high-temperature wear resistance.

Mg-rare earth (RE)-Zn alloys with long period stacking ordered (LPSO) phases have received extensive attention in the past few years because of their excellent mechanical properties compared with conventional wrought Mg alloys. However, the corresponding hot deformation behaviors and microstructure characteristics of Mg-RE-Zn alloys are rather complex. An in-depth investigation into this would broaden their engineering applications. In this work, hot compression experiments of solutionized Mg-10Gd-6Y-1.5Zn-0.5Zr alloys at 350-500 ^oC and a strain rate of 0.001-1 s^-1 have been conducted to investigate the hot deformation behavior, construct the hot processing map, and determine the hot working window. Afterward, the interaction between dynamic recrystallization (DRX) and kink deformation of LPSO phase during hot deformation has been studied through microstructure characterization. Results show that the flow stress decreases with the increase of temperature and the decrease of strain rate. When deformed at a relatively high strain rate, the sensitivity of flow stress to temperature is evident. When deformed at a relatively low temperature, the sensitivity of flow stress to strain rate is prominent. The corresponding hot processing map was constructed based on Murty criterion. Under a strain of 0.7, two optimal processing areas are found at 400-450 ^oC (0.001-0.027 s^-1) and 450-487 ^oC (0.12-1 s^-1). The accuracy of the constructed hot processing map has been verified by using microstructure characterization (via volume fraction analysis of recrystallized grains) of deformed samples, which correspond to different regions in the constructed hot processing map. By analyzing the softening stress of the flow curve at different temperatures (peak stress minus state stress), DRX volume fraction and kinking angle of the lamellar LPSO phase, the degree of kink deformation of the lamellar LPSO phase decreases with the increase of deformation temperature. In addition, the DRX volume fraction increases with the increase of deformation temperature. Moreover, the kink deformation of the lamellar LPSO phase has an inhibitory effect on DRX and the softening stress of the flow curve could be jointly affected by DRX and the kink deformation of the lamellar LPSO phase.

The dynamic fracture of metals in liquid state has become a subject of considerable interest in current times because of its observation in various physical and technological processes such as inertial confinement fusion and high-power laser-driven surface micromachining. In addition, it has been found that the fractures at elevated temperature are highly correlated with the microstructure of materials. He bubbles are frequently observed in many metals exposed to irradiation environments as a result of radioactive or self-irradiation. Both experimental and theoretical studies have indicated that He bubbles can substantially affect the mechanical properties of irradiated metals, resulting in hardening, swelling, and embrittlement. In recent years, attention has been drawn to understand the effects of He bubbles on the dynamic properties of materials, including shock compression, dynamic fracture, and surface ejection. This study examines the dynamic tensile fracture behavior of liquid aluminum containing He bubbles across a wide range of strain rates by utilizing molecular dynamics (MD) simulations and continuum modeling. The physical mechanism leading to the dynamic fracture is revealed to be predominated by the growth of He bubble. Under strain rates ranging from 3.0 × 10⁶ s^-1 to 3.0 × 10⁹ s^-1, tension primarily induces bubble growth. At higher strain rates, such as 3.0 × 10¹⁰ s^-1, both bubble growth and void nucleation-growth are observed, although bubble growth remains the dominant factor. The growth of He bubbles unfolds in two distinct phases: rapid growth followed by slower growth. These staged evolutionary characteristics appear to be consistent across strain rates, but the growth rate of helium bubbles markedly increases with increasing strain rates. Furthermore, the dynamic tensile strength at varying strain rates indicates a significant reduction for the metal containing He bubbles compared to the pure metal. However, this discrepancy decreases at extremely high strain rates, such as 3.0 × 10¹⁰ s^-1. In addition, a continuum damage model is constructed based on the insights obtained from MD simulations to describe the dynamic tensile fracture of liquid metal containing He bubbles. This model accounts for external tensile stress, internal pressure of He bubbles, inertia, viscosity, and surface tension. Theoretical calculations using the damage model and the binomial equation of state, which depict the pressure-volume relationship of the metal substrate, exhibit excellent agreement with MD data over a wide range of strain rates. This includes the evolution of the tensile stress and He bubble radius. The self-consistent MD-continuum model proposed in this study has the potential to be applied in macroscopic hydrodynamic simulations, to depict the dynamic tensile fracture behavior of liquid metal with He bubbles.

High-performance steels containing niobium have widespread use in high-end manufacturing sectors such as aerospace, automotive, energy, and construction engineering. Due to its capacity as a strong carbide-forming element, Nb favors the formation of NbC. These carbides, dispersed within the matrix, significantly contribute to precipitation strengthening, precipitation hardening, and grain refinement. In addition, Nb serves as a positive segregation element. When steel solidifies from its molten state, Nb segregates in the liquid phase and forms primary NbC carbides. These carbides significantly affect the mechanical properties of steel. Herein, to investigate the effect of Nb content on primary carbides in medium-carbon Nb-alloyed steel, the microstructure including the morphology, size, and distribution of niobium and carbon was characterized through SEM and TEM. To further understand the role of lattice vibrations and electrons at different temperatures, the first principle calculations with quasi-harmonic Debye model were combined to study the evolution of thermodynamic parameters. Primary carbides form because of solute segregation at the solid-liquid interface. For a more detailed investigation, a solute microsegregation model coupled with solidification phase transition was developed. This model was adopted to quantitatively analyze the effects of solidification phase transition and Nb content on solute microsegregation. The experiments yielded the following results: with increasing Nb content, the morphology of primary carbides shifted from spherical to polyhedral geometry. Furthermore, a distinct zonal distribution of primary carbides was observed. The laws of thermodynamics indicate that the increase in free energy change due to electrons at different temperatures is compensated by the decrease in free energy change arising from lattice vibrations, indicating the key role of lattice vibrations in maintaining the stability of NbC. The Gibbs free energy change at different temperatures was negative, indicating the thermostatic stability of NbC. Furthermore, the absence of imaginary frequency in the phonon spectrum indicates the dynamic stability of NbC. From a microsegregation viewpoint, the mass fraction of solute carbon decreases while that of the solute Nb increases at the solidification front during the phase transition from L + δ to L + γ. As the Nb content increases, the solid fraction of the solidification phase transition increases. Increased Nb content promotes the precipitation of primary carbides at low solid fractions.