The incoordination of strength-plasticity and the low thermal stability of alpha 2 phases seriously restrict the development of TiAl alloys. To overcome these shortcomings, Ti-48Al-2Cr-2Nb (at.%) alloys with superior mechanical performance and high thermal stability of alpha 2 phases were prepared by reasonably optimizing the printing strategy of selective electron beam melting (SEBM) in this work. The alloys exhibit the room-temperature compressive strength of 2716.08 MPa with 58.71 % fracture strain, and maintain compressive strength of 749.43 MPa at 850 degrees C. The improvement of strength-toughness and enhanced alpha 2-phase thermal stability are mainly attributed to the influence of long-period stacking ordered (LPSO) structures introduced via SEBM. High temperature and stress will induce the generation of high density 9R-type LPSO structures, and 9R structures can promote the orientation transformation of gamma phases. Abundant 9R structures and deformation twins play a key role in enhancing strength and toughness. Furthermore, this study reveals the transformation mechanism of 9R-type and 6H-type LPSO structures and first proposes three reaction pathways for the transformation from gamma to alpha 2 phases, with 6H phases serving as the intermediate structures. The three reaction processes are gamma -> 6H ->alpha 2, gamma -> 9R -> 6H ->alpha 2 and gamma ->gamma T -> 6H ->alpha 2, in which 9R and twin structures can transform into 6H configurations, promoting the transformation of gamma to alpha 2 phases. Due to gamma ->alpha 2 transformation induced by LPSO structures, the conventional decomposition reaction of alpha 2 phase is effectively inhibited, thus improving the stability of alpha 2 phases.

Previous studies have demonstrated the presence of numerous microscale inhomogeneities within bulk metallic glasses (BMGs), yet the issue of macroscale inhomogeneities in castings remains largely overlooked. In this study, the phenomenon of macroscale inhomogeneity in Zr-based BMG castings is discovered, and its underlying thermodynamic and kinetic mechanisms are elucidated by molecular dynamics (MD) simulations. A direct correlation between the casting modulus and cooling times was established to classify different characteristic regions in BMGs castings. The region with the highest casting modulus hosts the most significant composition deviation from the initial nominal composition. Instead, regions with lower casting modulus show composition closest to the initial nominal composition. These results underscore the importance of controlling cooling conditions to optimize macroscale inhomogeneity in large-scale BMGs casting, providing valuable insights for improving their application in advanced engineering fields.

Bulk metallic glasses (BMGs) have not been applied in engineering despite their great potential over the past few decades. The size and structural limitations in the formation of BMG components remain a bottleneck, which continues to be a significant challenge. This work overcomes that bottleneck by utilizing the advantages of counter-gravity casting technology, optimizing the casting processes, and successfully forming a Vit1 BMG bracket component with an outer diameter of 100 mm and a weight of 462 g. The results show that copper molds are not suitable for achieving a cooling rate higher than the critical rate required for glass transition in the entire component. Additional water cooling on the mold is necessary to achieve a sufficiently high cooling rate. Based on this, the melt pouring temperature, mold preheating temperature, and pressurization speed were carefully tuned to ensure complete filling of the mold cavity and stable melt flow during cavity filling. This work demonstrates that it is feasible to produce large-sized and complex BMG components by casting, paving the way for the large-scale application of BMGs in various fields.

Nano-additive manufacturing (NAM) endows the prospection to build complex 3D nano-sized structures with high flexibility, however it requires manipulating the liquid-solid phase transition at nano-scale resolution, which remains a great challenge. In this study, we realized controllable liquid-solid reversible phase transition of metallic nanoparticles by using electron beam irradiation. Alternating melting and crystallization were induced in Sn and In-Sn nanoparticles at the room temperature by applying an appropriate electron dose rate. For Sn nanoparticles, the temporal fraction of crystalline states can be quantitatively tuned from 1.41% to 90.58% by varying the dose rate from 2.21 × 105 to 0.66 × 105 A/m2, while the crystallization cycles increase from 11 to 26 and then decrease to 3. Similar behaviors were realized in the In-Sn system as well. This tunability enables precise control of the melting and crystallization behavior of an individual metallic nanoparticle by adjusting the electron dose rate. A quantitative thermal model is proposed that phase-dependent particle-substrate thermal conductance controls the balance between beam-induced heating and substrate heat dissipation, leading to temperature oscillations across the phase-transition threshold and enabling reversible melting-crystallization behavior.

As lightweight materials that are suitable for high-temperature operations, TiAl alloys are considered as the ideal materials for critical components in the aerospace field. The harsh service conditions necessitate that TiAl alloys possess the balanced strength-plasticity and great creep performance at high temperatures. To develop the high-performance alloys, Ti-48Al-2Cr-2Nb (at.%) alloys with the layered heterostructures were fabricated by controlling the 3D printing process during selective electron beam melting in this study. The high-temperature tensile tests demonstrate that the alloys exhibit excellent strength-plasticity synergy, characterized by the high elongation of 35.9 % while maintaining the ultimate tensile strength of 464 MPa at 850 °C. Meanwhile, compared with other additively manufactured Ti-48Al-2Cr-2Nb alloys, the alloys with heterogeneous microstructure in this study also show better high-temperature creep performance. The microstructural evolution behaviors during creep are investigated, which is mainly manifested by the growth of α2 phase and the coarsening of α2 lamellae, attributed to the long-period stacking ordered 6H structures assisted phase transformation from γ to α2. Furthermore, the formation mechanisms of twins and twin intersections are revealed, and their transformation into 6H structure further promotes the γ→α2 phase transformation process. Finally, by comparing the microstructure and texture characteristics, this work provides novel insights into the texture formation and evolution of α2 phase under the effect of high temperature and stress.

High-temperature creep resistance is a key requirement for structural materials used in aerospace applications. However, this property remains poorly understood for the EV31 alloy. This study investigates the creep mechanisms of EV31 alloy in temperature range from 200 °C to 300 °C through experimental characterization of creep curves and microstructures after creep deformation, combined with extracting the stress exponents and creep activation energies. The results show that the stress exponent (n) is primarily in a range of 4–6, but decreases to approximately 2.5 during creep deformation at 300 °C. The measured activation energy exceeds the lattice self-diffusion activation energy of α-Mg (135 kJ·mol−1). Microstructural observations reveal that the creep samples contain precipitate phases, mainly β′ and β1 within grains and β phase at grain boundaries, with precipitate-free zones forming on one side of the grain boundaries. Dislocation pile-up and tangle are observed around grain boundaries during creep at 250 °C. At 300 °C, dislocations are present within the grains and are hindered by the β′ phase. Based on these findings, it is concluded that the creep deformation of the EV31 alloy is dominated by mixed mechanisms. The grain-boundary gliding mechanism operates throughout the entire temperature range and dominates creep deformation at temperatures near 200 °C by mixing with dislocation creep. Dislocation climbing is the dominant mechanism at around 250 °C. At 300 °C, creep proceeds via precipitate-induced drag on dislocation motion, accompanied by grain-boundary gliding. This work casts new light on the development of high creep resistant magnesium alloys based on EV31 alloys and also provides critical information for EV31 alloys using at elevated temperatures.

Casting porosity defects constitute a critical bottleneck hindering the engineering application of bulk metallic glass (BMG). Their formation mechanisms remain insufficiently elucidated due to the unique rapid vitrification process inherent to BMG. This study investigated a Zr‑based BMG, employing multi‑scale characterization and thermodynamic analysis to reveal the formation mechanisms of porosity defects. The results indicate that gas pores are the predominant type of porosity defect. The fundamental cause lies in the layer‑by‑layer-like solidification mode, in which the rapid advance of the supercooled melt from the casting surface toward the core kinetically traps bubbles. Melt-turbulence-driven gas entrainment is the primary gas source for pore formation, while oxide inclusions interact with pre-existing bubbles, reduce the bubble nucleation energy barrier, and promote bubble retention in the melt. This work demonstrates that achieving smooth melt filling coupled with melt purification provides a viable pathway for controlling porosity defects, thereby furnishing a theoretical basis for producing high‑quality BMG castings.

High-performance magnesium alloys are in great demand to meet the lightweight design requirements of aircraft. Grain size has long been recognized as a key factor influencing the mechanical properties of alloys. This study investigates the effect of grain size, controlled by Zr addition, on the fatigue behavior of a recently developed low-cost Mg-2.6Nd-0.35Zn alloy, through systematic characterization and analysis of stress-life (S-N) curves, fatigue crack propagation, fracture surface morphology, stress intensity factor, and crack propagation threshold. The results show that after heat treatment (solution at 525±5 °C for 8 h and water quenching at 60–80 °C, followed by aging at 250±5 °C for 14 h and then air cooling), coarse-grained specimens (average grain size approximately 596 µm) containing 0.12wt.

The sintering microstructure and densification behavior of the spherical and irregular tungsten powders prepared by hot pressing(HP)and hot isostatic pressing(HIP)were systematically investigated.In the results,the irregular FW9 powders achieve the densification through coupled grain boundary diffusion and plastic flow during HIP stage,whereas the spherical SW15 and SW25 powders exhibit the progressively reduced densification efficiency dominated by plastic flow and surface diffusion mechanism,respectively.Notably,the broad particle size distribution of SW25 powders critically constrains the densification process.The FW9 sintered compacts display the average dislocation density of 0.577×1014 m-2,the low-angle grain boundaries(LAGBs)of 24.4％,the wide grain size distribution of 25～250 μm,and the average grain size of 76.04 μm with the pronounced crystallographic texture.In contrast,the SW15 and SW25 sintered compacts show the higher average dislocation densities of 0.800×1014 m-2 and 1.300×1014 m-2,the elevated LAGBs area fractions of 62.4％and 75.0％,and the uniform grain sizes of 44.68 μm and 50.15 μm,respectively,without the preferential orientation,indicating the intensified lattice distortion and plastic deformation in spherical powders during sintering.It is demonstrated that the spherical powders significantly enhance the grain size uniformity,suppress the abnormal grain growth,and avoid the texture formation,providing the critical insights for tailoring high-performance tungsten sputtering targets through powder morphology optimization.

Vacuum induction melting (VIM) of recycled powder with bulk master alloy represents an industrialized approach for recycling metallic waste. However, the intrinsic mechanisms governing the co-melting behavior of materials with distinct melting characteristics, such as powder bed and bulk alloy, remain insufficiently understood. To address this, a coupled multiphysics model was developed to simulate the evolution of induction melting involving homogeneous alloys with different morphologies. This model integrates magnetic, electric, and phase-field dynamics while incorporating melt convective heat transfer, thereby establishing a fully coupled electromagnetic-thermo-hydrodynamic framework. Through this modeling approach, the entire VIM process of melting homogeneous alloy with different morphologies can be comprehensively analyzed. The validity of the model was verified via small-scale VIM experiments using FGH96 powder/bulk composite, supported by infrared temperature measurements. This simulation methodology is not only applicable to small-scale recycling but can also be extended to large-scale industrial production, providing a reliable theoretical foundation for the recycling of powder materials.

FeCoCrNiMn high-entropy alloy coatings were deposited on 304 stainless steel substrates via atmospheric plasma spraying, and the tribocorrosion wear behaviors of these FeCoCrNiMn high-entropy alloy (HEA) coatings in 3.5 wt.

This study investigates Y content effects on microstructure and mechanical properties of Mg–xY–2.2Nd–1.0Gd–0.5Zr alloys (x = 3.0, 3.5, 4.0, 4.5 wt

To meet the lightweight demands of aerospace applications, rare-earth magnesium (Mg-RE) alloys are increasingly utilized. However, issues related to casting defects have grown more prominent, demanding detailed research and effective control. This study investigated the fluorescent linear defects observed in WE43 (Mg-Nd-Y-Zr) alloy casing components via sand mold low-pressure die castings (LPDC). The composition and structure characteristics of the linear defects were systematically revealed, and nanoindentation testing was conducted to quantitatively analyze the mechanical properties of linear defect oxide films. It was revealed that fluorescent linear defects are formed by multi-scale and multi-morphology double oxide films (bifilms). The oxide film demonstrated high mechanical strength, primarily attributable to its dense Y2O3 composition. Its hardness was 10.8 GPa and elastic modulus was 140.1 GPa. These mechanical properties enable the oxide film to maintain structural integrity during melt folding and convergence, thereby promoting the development of continuous linear defects. Analysis of the casting structure and mold filling flow field demonstrated that melt confluence and backflow during filling induce folding and entrapment of surface oxide films, resulting in the bifilms exhibiting linear fluorescence. Based on the regulation of the filling flow field,the designed inclusion collection unit effectively mitigated fluorescent linear defects in Mg-RE alloy castings by redirecting melt confluence and entrapping oxide inclusions within its designated region.

The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn (EV32) alloy. The findings indicate a significant increase in the ignition point of the alloy upon Y addition, notably reaching 813.9 °C for the EV32–3Y (wt.%) alloy. Additionally, the calculated residual stresses of the Y2O3 and Gd2O3 films were 2.732 GPa and 2.569 GPa respectively, showcasing a distinct correlation between Y concentration and improved fire resistance. This enhancement can be attributed to the formation of denser oxide films, especially Y2O3 and Gd2O3, effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing. The study elucidates the vital role of Y addition in enhancing fire resistance, thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure. These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.

Zr-based amorphous alloys are pivotal for structural applications, yet interfacial reactions with refractory ceramics during vacuum induction melting (VIM) remain underexplored, critically limiting large-scale and high-quality production. The reaction mechanisms between Zr-based melts and five industrial refractory oxide ceramics (Al2O3, MgO, ZrO2, Y2O3 and SiO2) were revealed, aiming to guide industrial optimization. VIM experiments, combined with oxygen detection, in-situ wettability measurements, and SEM-EDS characterization were conducted to quantified impurity element diffusion. Thermodynamic and kinetic analyses were employed to interpret interfacial behaviors. The established thermodynamic framework and kinetics model enable prediction of reaction layer formation and impurity contents under varying VIM process parameters. Furthermore, capillary-driven infiltration was theoretically analyzed, and melt-induced ceramic erosion was quantified via numerical simulation of convection. These findings provide a universal framework for interfacial engineering in reactive alloy systems, guiding industrial metallurgy procedures to produce high-quality amorphous alloys.

The bulk metallic glasses (BMGs) casting process should consider the glass transition and melt filling simultaneously, which is dependent on the melt fluidity and casting conditions. However, the impact of casting processes on the melt solidification and flow behavior of BMGs melt has not been thoroughly studied. Herein, the effect of cooling conditions on melt fluidity and microstructure of Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMGs was systematically investigated by controlling the melt overheat and mold preheating temperature. The fluidity model for BMGs melt in a semicircular straight cavity was established, and the flow length of the melt under different cooling conditions was calculated based on the heat balance theory. The microstructure of the BMGs was characterized by using XRD, SEM, DSC and TEM. The results reveal that increasing melt overheat is more effective than raising mold preheating temperature in enhancing melt fluidity. Increasing them would lead to an increase of the order degree of the BMGs castings and crystallization, which is mainly related to the increase of critical cooling rate of BMGs. This work can provide a reference for the development of BMGs casting process.

The highly spontaneous burning of magnesium alloys severely hinders their safe production and application. However, a clear understanding of the burning mechanism has been lacking. The present work in situ investigates the burning behavior of EV31 magnesium alloys with neodymium addition. Ignition modes, starting from the fully molten state, were observed, in contrast to the proposed solid-state ignition and microscale pre-melt pool ignition modes. The ignition was triggered by the extremely rapid oxidation of the melt leaking from cracks in the surface oxide shell at temperatures much higher than the melting point. Fresh cracks and new oxide films formed at these cracks were observed on the burning sample’s surface upon in situ fire extinguishing, providing strong evidence to support the hypothesis that ignition is initiated by cracks in the surface oxide film. Neodymium addition reduced the cracking of the surface oxide shell and increased the ignition temperature in a linear relationship within the currently investigated content range 3−15 wt

As a fast developed magnesium alloy family, Mg-Nd-Zn alloys show great application prospect in varied fields. However, the grain refinement behaviors of this alloy family were still unclear. The present work investigated the process dependence of grain refinement effect by Zr refiner for the alloy. Gradually saturation of Zr dissolving as function of stirring time and melt temperature were revealed, giving out a saturate content of soluble Zr about 0.72 wt.%. The dissolve of Zr refiner undergoes three stages with increasing the added Zr refiner, respectively giving rise to grains microstructure without Zr-rich particles, single core Zr-rich particles and multi-shell particles. Most significant grain refinement effect occurred in the first stage without Zr-rich particles formation, due to refinement mechanism proved to be the grain growth restriction. The multi-shell Zr-rich particles were observed, for the first time, with soluble Zr beyond 0.68 wt.%. A limited Zr diffusion model was proposed to understand the formation of such multi-shell Zr-rich particles. Moreover, the Zr-rich particles evolution behaviors were revealed dependent on the melt holding time, building the relationship between Zr-rich particles and the grain refinement recession. The results shed new lights on the grain refinement process design of Mg-Nd-Zn alloys family.

The production of larger hot-work die steels has become a prevailing industrial trend. This study addressed the challenge of predicting and controlling the complex multiphase microstructures formed through isothermal treatment near the martensite start temperature (Ms), which result from sluggish core cooling during quenching of large-scale hot-work die steels. Using spray-formed H13 steel, we systematically investigated the coupled effects of near-Ms isothermal quenching on microstructure and mechanical properties through dilatometry testing, multi-scale characterization (SEM/EBSD/TEM/XRD), and mechanical testing. The influence mechanisms of subsequent tempering processes were further elucidated. The results demonstrate that quenching at 220 degrees C (below Ms) produces a composite microstructure of nano-structured bainite, tempered martensite, and retained austenite. This microstructure exhibits the finest grain size (1.66 mu m) and approximately doubled impact energy (11.3 J/cm(2)) compared to specimens quenched at 260 or 300 degrees C (above Ms), which exhibited similar to 5.7 J/cm(2). The enhancement primarily originates from grain refinement strengthening, TRIP effect enabled by high-stability retained austenite, and absence of brittle carbide precipitation. During 350 degrees C tempering, specimens isothermally quenched above the Ms point exhibit improved toughness due to dissolution of brittle acicular M3C carbides and stabilization of retained austenite. In contrast, 500 degrees C tempering causes drastic toughness deterioration (approximate to 3 J/cm(2)) through precipitation of semi-coherent acicular M7C3 carbides and aggregated nanoscale carbide precipitation. Tempering at 650 degrees C resulted in complete decomposition of retained austenite, accompanied by a sharp reduction in dislocation density and precipitation of large elliptical M23C6 carbides, resulting in a marked decrease in strength and a significant improvement in toughness.

This study investigates the tensile properties of GdDyCoAl-based high-entropy amorphous microwires. The microwires exhibited brittle characteristics, showing no plastic deformation during tensile testing. Among the four compositions, Ho20Gd20Dy20Co20Al20 achieved the highest fracture strength of 1147 MPa, while Sm20Gd20Dy20Co20Al20 exhibited the most consistent mechanical behavior. Fracture strength data were analyzed using Weibull distributions, with the three-parameter Weibull model providing the best fit. Fracture morphology displayed typical amorphous features, including vein-pattern zones and shear bands, confirming brittle fracture under tensile stress. These findings enhance understanding of the mechanical reliability and stability of rareearth-based high-entropy amorphous microwires.