The tensile creep behavior of the refractory high-entropy alloy (VNb)80(TaTi)20 is investigated at elevated temperatures (1023-1123 K) under the applied stresses ranging from 200 to 400 MPa and a relatively low vacuum condition of 1 & times; 10-2 Pa. The creep behavior at 1073 K follows a power law, with a stress exponent of 3.0 +/- 0.4 and an activation energy of 283 +/- 13 kJ mol-1, indicating a solute drag mechanism, which is also evidenced by the dispersed dislocations without entanglements. The fracture surfaces of the post-creep specimens display brittle intergranular cracking, resulting from the significant oxidation during the creep test. A surface oxide layer forms rapidly and continues to thicken, accompanied by grain boundary oxidation and internal oxidation. These processes induce surface degradation, stress concentration, and weakening of grain boundaries, thereby accelerating localized creep deformation. Conversely, creep deformation disrupts the oxide layer, generates fresh surfaces that enhance oxygen diffusion, and promotes further localized oxidation. This synergistic interaction between creep and oxidation results in premature intergranular fracture and material failure, which eventually leads to reduced creep life and lower creep strain in the (VNb)80(TaTi)20 alloy. Nevertheless, this alloy still outperforms major reported RHEAs with its low steady-state creep rates under the present testing conditions, demonstrating a superior creep resistance. These findings provide a valuable insight into the creep mechanisms and oxidation-coupled deformation behavior of (VNb)80(TaTi)20, offering important guidance for the design of advanced refractory high-entropy alloys with improved creep resistance and oxidation stability.

Experiments consistently show that dilute boron additions can refine grains, suppress processing defects, increase strength, and reduce intergranular fracture in polycrystalline molybdenum, yet the atomistic origin of this strength--damage-tolerance combination remains unresolved. Here, density-functional-theory calculations resolve the effect of B on three distinct defect processes: migration of $1/2\langle111\rangle$ screw dislocations, incipient shear, and separation of six symmetric tilt grain boundaries. B binds to the screw-dislocation core by up to 1.44~eV and drives an easy-to-hard core reconstruction. Once trapped, B raises the calculated Peierls stress from 1.79 to 5.26--7.19~GPa and the zero-stress kink-pair formation energy from 1.27 to 1.98--2.32~eV, identifying solute pinning as an intrinsic strengthening mechanism. By contrast, B lowers the unstable stacking-fault energy, reducing the energetic scale for incipient shear in the modeled geometry. B also segregates favorably to nearly all sampled grain-boundary sites and increases the work of separation for most configurations. Combining these quantities in a Rice--Thomson-inspired ratio shows that B shifts the local slip-to-cleavage balance toward plastic accommodation. These atomistic trends are consistent with three independent experimental observations in B-containing Mo: grain-boundary enrichment, strengthening, and reduced intergranular damage. The resulting defect-resolved strength--fracture map provides a transferable first-principles workflow for screening trends in BCC refractory metals.

Elements segregation can significantly affect grain boundary (GB) strength, altering the thermal stability and mechanical properties of materials. In this work, we systematically investigate the synergistic effects between solute rhenium (Re) and interstitial carbon and oxygen (C and O) atoms at molybdenum (Mo) GBs and their influence on GB strength through first-principles calculations. Our results demonstrate that both C and Re segregation enhances GB strength, while O segregation significantly deteriorates interfacial cohesion. The co-segregation and co-strengthening energies of ReC and ReO are found to be lower than the sum of their individual values, indicating their repulsive interactions. Notably, ReC co-segregation leads to further GB strengthening, while ReO co-segregation effectively alleviates oxygen-induced embrittlement. Electronic structure analysis reveals that the chemical interactions dominate the repulsive behavior: ReC repulsion originates from direct antibonding states, whereas ReO repulsion is primarily caused by the breaking of MoO bonds. Furthermore, the formation of MoC and MoRe bonds enhances GB cohesion, while oxygen induces the weakening of MoMo metallic bonds. This work provides fundamental understanding of solute-interstitial interactions at atomic scale and offers valuable insights for designing high-performance refractory alloys.

Nickel-based superalloys are key structural materials for critical applications in extreme service environments,such as in aero-engines and nuclear reactors.However,under neutron irradiation,helium(He)is generated within the material via transmutation reactions.These helium atoms segregate and accumulate at defects like grain boundaries(GBs),leading to severe hardening and embrittlement(known as"helium embrittlement"),which significantly limits the material's long-term service life. To gain a deeper understanding of and mitigate helium embrittlement,this study employed first-principles calculations based on density functional theory(DFT)to systematically investigate the synergistic effects of four key alloying elements(Cr,Mo,Nb,Ti)and helium in four typical symmetric tilt grain boundaries(Σ3(111),Σ11(113),Σ5(210),and Σ5(310))of nickel.Key thermodynamic parameters,such as segregation energy and strengthening/embrittling energy,were calculated.This was complemented by electronic structure analyses,including differential charge density and density of states,to elucidate,at the atomic and electronic levels,the influence of alloying elements on helium segregation behavior and the microscopic mechanisms by which they mitigate grain boundary embrittlement. The segregation energy calculations show that both the alloying elements and helium atoms exhibit a tendency to segregate to the grain boundaries.A clear correlation exists between the segregation energies and the relative atomic excess volume,with larger excess volumes yielding more negative segregation energies.Interstitial helium possesses the largest relative atomic excess volume,resulting in the strongest segregation tendency.Although the introduction of alloying elements cannot completely prevent helium segregation,it can reduce its driving force for segregation. Calculations of the strengthening energy indicate that when alloying elements like Cr,Mo,Nb,and Ti segregate to the grain boundaries,they generally reduce the embrittling energy of He.This mitigating effect is more pronounced at grain boundaries with higher formation energy,such as Σ5(310).Among the four elements,Mo exhibits the strongest and most stable inhibitory effect,reducing the embrittling energy of substitutional He by approximately 11％to 16％and that of interstitial He by 3％to 10％. Electronic structure analysis reveals the underlying mechanism:The segregation of helium atoms causes electron depletion in the surrounding Ni-Ni bonds,weakening their bonding strength.In contrast,the alloying elements form strong chemical bonds with neighboring nickel atoms,increasing the electron density in the grain boundary region.This partially compensates for the electron depletion induced by helium,thereby protecting the grain boundary bonding and mitigating embrittlement. This study clarifies the physical essence of how alloying elements inhibit helium embrittlement through an electronic compensation mechanism,providing an important theoretical basis for the compositional optimization and design of nickel-based superalloys with high resistance to irradiation and helium embrittlement.

Machine learning in materials science is often limited by black-box predictions and scarce experimental data, which hinder reliable discovery and mechanistic understanding. Here we present SEAM, a self-explaining attention network that embeds interpretability directly into model architecture rather than relying on post-hoc analysis. SEAM records physically meaningful information during prediction through attention mechanisms and integrates multi-method cross-validation using attention analysis, integrated gradients, and SHAP to ensure robust interpretation. Specifically, Bayesian optimization enables automatic adaptation, achieving a predictive accuracy of R2=0.84 for the ductility of molybdenum-based refractory alloys. By distinguishing causal mechanisms from spurious correlations, SEAM reveals a critical “correlation inversion” for Tungsten: while statistically correlated with high ductility, decoupling analysis identifies W as an intrinsic embrittler. This is validated by complementary first-principles calculations showing Re-induced bond softening versus W-induced stiffness preservation. This integrated framework bridges data-driven prediction with physical understanding, enabling trustworthy learning and rational design in data-scarce and mechanistically complex materials systems.

Zirconium (Zr) redistribution significantly impacts the in-reactor properties of U-10Zr metallic fuel. Although several thermodynamic models have been established, the underlying microscopic diffusion mechanisms remain unclear. Recent experimental results suggest that Zr atoms may first segregate and then rapidly diffuse along grain boundaries (GBs). In this study, molecular dynamics simulations are carried out to investigate Zr segregation at GBs in alpha U-Zr, and to improve our understanding of grain boundary segregation behavior in lowsymmetry structures. Two sets of symmetric tilt grain boundaries, comprising a total of 25 GBs in alpha-U, demonstrate anisotropic behavior in terms of structural thermal stability. The segregation energy calculations indicate that Zr atoms preferentially segregate to high-energy GBs rather than to low-energy ones, owing to their larger atomic free volumes. Monte Carlo simulations further show a positive correlation between the saturation concentration of Zr segregation and GB energy. Moreover, the results indicate that Zr atoms are more prone to segregate at GBs with increasing temperature and bulk Zr concentration. These results provide a thermodynamic basis for subsequent studies of Zr grain boundary diffusion in alpha-U.

The formation behavior of point defects in FeCrSi alloy were studied using first principles. The results show that the addition of Si significantly reduces the vacancy, tetrahedral and octahedral interstitials formation energy in FeCr alloy. However, the formation energy of interstitial atom pairs in the three < 110 > directions increases after the addition of Si, which implies that the formation of interstitial atom pairs is more difficult. The addition of Si widens the pseudogap, weakens the electron interaction between atoms, and reduces the hindrance to vacancy formation, resulting in a decrease in vacancy formation energy. Moreover, the DOS curve of the model containing vacancies has a lower peak compared to the perfect model, indicating weakened electron localization and reduced electron interaction between atoms around vacancies in FeCrSi alloys. Additionally, by comparing the differential charge density maps before and after the addition of Si, it can be found that the addition of Si weakens the electron interaction between atoms, which is consistent with the DOS analysis results and the vacancy formation energy calculation results. These results provide a scientific basis for the irradiation performance prediction defect evolution of FeCrSi steel.

A solute is useful at a grain boundary only if it both occupies the interface and preserves or improves cohesion. Using first-principles calculations on six symmetric tilt grain boundaries in molybdenum, we establish a site-resolved segregation--cohesion framework for Re and Zr. The framework combines segregation energy with Rice--Wang strengthening energy and is validated by rigid-separation tensile tests for representative $\Sigma3(111)[1\bar{1}0]$ and $\Sigma5(310)[001]$ boundaries. Re frequently satisfies both requirements for useful interface regulation: favorable segregation and negative strengthening energy. Zr is more structurally selective; even when it segregates favorably, it often gives positive strengthening energies and lowers the resistance to ideal decohesion. Tensile calculations reproduce this contrast, with Re increasing fracture energy and ideal tensile strength, whereas Zr reduces both. Solute-centered charge-density profiles show that both solutes occupy electronically active GB-core regions but perturb the local electronic environment differently. The main result is a practical design rule for Mo internal interfaces: screen solutes by coupled segregation and cohesion, not segregation energy alone.

Molecular dynamics simulations were carried out to study the effect of chemical short-range order (CSRO) on the primary radiation damage in TiVTaNb high-entropy alloys (HEAs). We have performed displacement cascade simulations to explore the CSRO effect on the generation and evolution behaviors of irradiation defects. The results demonstrate that CSRO can suppress the formation of Frenkel pairs in TiVTaNb HEAs, with the suppression effect becoming more pronounced as the degree of CSRO increases. CSRO can change the types of interstitial defects generated during cascade collisions. Specifically, as the degree of CSRO increases, the proportion of Ti-related interstitials shows a marked enhancement, primarily evidenced by a significant rise in Ti-Ti dumbbells accompanied by a corresponding decrease in Ti-V dumbbells. CSRO exhibits negligible influence on defect clustering and the nucleation and evolution of dislocation loops. Regardless of CSRO conditions, TiVTaNb HEAs preserve exceptional radiation tolerance throughout the cascade damage process, suggesting that the intrinsic properties of this multi-principal element system dominate its radiation response. These findings provide fundamental insights into the CSRO effect on defect formation and evolution behaviors in HEAs, which may provide new design strategies for high-entropy alloys.

In this work, a creep rupture life prediction model is proposed by combining the creep constitutive laws and Monkman-Grant (M-G) relation to analyze the rupture time under thermal and irradiation creep. The model could simultaneously characterize the influence of testing temperature, applied stress and irradiation damage on the steady-state creep strain rate by taking into account corresponding microstructure evolution, accurately capture the mechanism transitions during creep, and then convert the steady-state creep strain rate into macroscopic rupture life via the M-G relation. Once the irradiation effect is ignored, the model can be degraded to predict the thermal creep rupture life. Model validation is achieved by comparing theoretical results with the experimental data of 15-15Ti, 316H, P92 and 304 steels for both thermal and irradiation creep. Related mechanism analyses indicate that the shortened thermal creep rupture life with increasing stress and temperature is mainly ascribed to the accelerated activity of dislocation climb that leads to the enhancement of dislocation mobility and acceleration of creep damage accumulation. Under irradiation creep, it is the elevated vacancy diffusion coefficient that leads to the enhanced activity of dislocation climb, and finally results in the shorter irradiation creep rupture life when compared with the one under thermal creep. The proposed model could provide an efficient theoretical tool for material creep life assessment under extreme environments.

Computer vision (CV) techniques have been increasingly adopted to the quantitative analysis of metallic microstructures, offering new opportunities for automated feature extraction and microstructural characterization from microscopy images. This review presents a focused and application-oriented overview of CV-based approaches for metallic microstructure analysis, with particular emphasis on the roles and complementarities of semantic segmentation and object detection tasks. The workflow from image preprocessing and microstructural feature identification to quantitative descriptor extraction and microstructure-property correlation is systematically discussed. Representative applications in defect quantification, mechanical property evaluation, and performance-oriented materials design are summarized, together with current limitations related to data availability, generalization, and physical interpretability. This review aims to provide practical guidance and a structured reference for researchers seeking to adopt CV techniques in materials microstructure analysis.

Irradiation induced mechanical property degradation is a key issue concerned for the structural materials used in nuclear reactors. As a typical refractory high-entropy alloy (RHEA), VNbTaTi garners significant attention for its excellent high-temperature mechanical properties and thermal stability, which grant it promising application potential in nuclear engineering. In this study, the microstructural and mechanical property changes induced by proton irradiation are investigated in VNbTaTi by combining various micro mechanical test methods including nanoindentation, micropillar compression, and micro tensile tests, with the elemental metal V as a reference material. The irradiation hardening in VNbTaTi is significantly suppressed compared with that of V. More excitingly, the tensile ductility in this RHEA retains well after irradiation, which is in sharp contrast with V, which almost completely loses its ductility in even lower irradiation dose. The core reason for the improved resistance to irradiation hardening and embrittlement is that the defect formation and aggregation are strongly suppressed in VNbTaTi as evidenced by the lower defect size and density. Both VNbTaTi and V exhibit deformation localization after irradiation due to the interaction between gliding dislocations and irradiation defects, but to qualitatively different extents. Unlike V, in which most deformation concentrates in the top region of irradiated micropillars, the VNbTaTi micropillars generally deform uniformly but with the formation of several hundred-nanometer-scale dislocation channels.

15-15Ti austenitic stainless steel has high-temperature creep resistance and irradiation stability due to dispersed TiC nanoprecipitates in the material. In this study, we employ Small-Angle Neutron Scattering (SANS), Xray Diffraction (XRD), Transmission Electron Microscopy (TEM), Electron Backscatter Diffraction (EBSD), and Neutron Diffraction to investigate the evolution of TiC nanoprecipitates and dislocation density during creep (at 625 degrees C and 350 MPa) and heat treatment at the same temperature. The results reveal that during creep, TiC precipitates undergo rapid nucleation and growth, followed by a steady-state phase, and then a second rapid growth phase until creep fracture, with the final average diameter remaining below 10 nm. In contrast, during heat treatment, TiC precipitates also nucleate and grow rapidly but subsequently stabilize at a smaller average size than those observed in creep samples. Notably, a significant reduction in dislocation density during the tertiary creep stage is evidenced by a sharp drop in SANS data in the high-Q range, corroborated by TEM and XRD. This reduction was not observed during heat treatment. The regrowth of TiC precipitates during creep is closely associated with dislocation density reduction. These findings demonstrate that TiC precipitate regrowth is intrinsically linked to dislocation annihilation during creep deformation. The applied creep strain promotes dislocation motion, while the high binding energy between Ti/C solutes and dislocations facilitates efficient solute transport via dislocation migration. When these solute-laden dislocations interact with existing TiC precipitates, they become pinned, creating localized regions of Ti and C supersaturation that drive precipitate regrowth.

The synergistic co-precipitation of Cu-rich phases and manganese-nickel-silicon-dominated phases (MNSPs include T6 and T3 phases) plays a critical role in the irradiation embrittlement of reactor pressure vessel (RPV) steels. In this work, a five-component Fe-Cu-Mn-Ni-Si multiphase-field model is developed to describe the coupled evolution of the ferritic matrix, Cu-rich phase, T3 phase, and T6 phase. The simulations reveal a composition-dependent transition in the precipitation pathway. In high-Cu alloys, Cu, Ni, and Si first form solute clusters, while Mn partitions more slowly; with further evolution, Cu becomes enriched in the core and Mn-Ni-Si segregates around it, producing a Cu-rich core/Mn-Ni-Si-enriched shell morphology. In low-Cu alloys with high Mn-Ni-Si supersaturation, trace Cu accelerates early solute clustering, but subsequent precipitation is dominated by Mn-Ni-Si phases. T6 forms first as the main precipitate phase, whereas T3 appears later at the T6/matrix interface after local solute redistribution. Increasing the Mn or Si concentration weakens this coupled T6/T3 pathway and promotes separate precipitation of T6 and T3. In realistic low-solute compositions, a pre-existing T6-like embryo remains stable and grows by absorbing dilute Mn, Ni, and Si from the matrix, while T3 enrichment appears only after T6 growth slows. These results suggest a sequential chemical-precipitation mechanism in which residual Cu promotes early solute clustering, T6 governs the principal growth stage, and delayed T3 interfacial enrichment accompanies late-stage stabilization. The seeded calculation evaluates the conditional growth of an assumed T6-like embryo and does not model defect-assisted nucleation.

Advanced nuclear reactors require materials with excellent performance under harsh conditions. Molybdenum (Mo) and its alloys are key candidates for cladding and core structural applications due to their high-temperature properties. However, balancing strength and plasticity in Mo alloys remains challenging, as most alloying elements focus on strengthening with less obvious toughening effects. The complex interactions of alloying elements are difficult to fully understand through traditional testing alone. To address this, materials genetic engineering leverages data-driven approaches to predict and optimize material properties, accelerating R&D cycles. In this study, a BPNN regression model optimized by Bayesian methods was developed based on a dataset of 177 Mo-based alloy samples with 38 compositions, focusing on tensile strength and elongation at elevated temperatures. The model achieved an R-2 value of 0.83 and was used to predict the effects of various single and multi-element additions on alloy performance. Results indicate that Re (similar to 15 wt%), Zr (similar to 0.08 wt%), and Ti (similar to 0.2 wt%) additions, with minimal N content (<0.0025 wt%), optimize the strength and toughness of Mo alloys at 800 degrees C.

In body-centered cubic metals such as molybdenum, screw dislocations critically govern the plastic deformation behavior of alloys. The presence of solute atoms in alloys can effectively alter the formation and movement of screw dislocations. In this study, we employed first-principles calculations to delve into the electronic origins of these influences. Initially, we constructed single atomic column and triple atomic column models to simulate the formation of screw dislocations with solute atoms. Our investigation revealed that tantalum (Ta) and tungsten (W) increase the formation energy of solute-dislocation interactions, while osmium (Os), iridium (Ir), and platinum (Pt) have the opposite effect. Subsequently, utilizing a screw dislocation dipole model under shear deformation, we explored the combined effects of solute atoms and deformation on dislocation core movement. We found that Os, Ir, and Pt, located as the first nearest neighbors of the dislocation core, exhibit an attractive effect on the dislocation core. Solute atoms at specific positions can alter the direction of dislocation slip, inducing cross-slip and enhancing material ductility. In contrast, under the same stress, Ta and W exhibit repulsion towards the dislocation core and cannot change the direction of dislocation slip, only altering the energy barrier for dislocation core movement. This work provides atomic-scale insights into solute-induced dislocation dynamics, offering guidelines for advanced Mo alloy design.

Irradiation embrittlement occurs in the cladding materials of fusion reactors during irradiation. Determining the ductile–brittle transition temperature via Charpy impact testing is the primary method for evaluating irradiation embrittlement. Standard-sized V-shaped Charpy impact specimens (CVN) are too large in size and have high induced radioactivity. Small-sized specimens (KLST) can solve these problems, but the performance data measured from small-sized specimens are different from those of standard specimens. In other words, there is a size effect in impact performance. The notch size and hammer impact speed of KLST specimens are different from those of CVN specimens. The influence of these factors on impact performance requires further study. In response to these issues, on the basis of the previous experiments conducted by the research group, GTN damage models of CVN specimens and KLST specimens are constructed using the inverse operation method. Numerical simulation of the impact on the upper platform area is carried out for KLST specimens and variable-sized KLST specimens. Compared with the test results, the numerical simulation results are in good agreement, verifying the accuracy and reliability of the model. The results show that the notch angle and radius have little influence on the plastic zone. The cross-sectional area of the notch has a significant impact on the plastic zone. The impact velocity within the range of 3.8 m/s to 5.24 m/s affects the impact response process, but does not affect the load–displacement curve, the length of the non-plastic deformation zone, or the volume of the plastic zone.

Refractory high entropy alloys (RHEAs) have recently gained much attention as potential structural materials in advanced reactors, where they may suffer from the synergistic threatens from both displacement damage and transmutation-induced He, calling for the necessities of understanding the He bubble behavior in these novel alloys. In this work, VTaTi is selected as a model RHEA, and the formation of He bubbles under 2.5 MeV He ion irradiation at various temperatures (i.e., room temperature, 400, and 700 degrees C) is compared with elemental V, which shares the same body-centered cubic (BCC) structure. Unlike the cases for the widely studied 3d-transition-metal HEAs, in which increasing compositional complexity generally assists in suppressing the bubble growth, here the sizes and the total volume fractions of He bubbles in VTaTi are larger than those in V at all the three irradiation temperatures. First-principles calculations are performed to unveil the underlying mechanisms through the comparison of typical defect energies associated with classical He diffusion models. The lower vacancy formation energy, reduced He migration energy, and lower binding energy of He-vacancy complexes may contribute to the promoted He aggregation in VTaTi.

Ferritic/martensitic (F/M) steel is a candidate material for key structures in fourth-generation nuclear energy systems (such as fusion reactors and fast reactors). Irradiation hardening behavior is a core index to evaluate the material’s stable performance in a high-neutron-irradiation environment. In this study, based on 2048 composition and property data, a correlation model between key elements and their interactions and irradiation hardening in F/M steel was constructed using a Bayesian optimization neural network, which realized quantitative prediction of the effect of composition on hardening behavior. Studies have shown that the addition of about 9.0% Cr, about 0.8% Si, Mo content higher than about 0.25%, and the addition of Ti, Mn can effectively suppress the irradiation hardening of F/M steel, while the addition of N, Ta, and C will aggravate its irradiation hardening, and the addition of W and V has little effect on the irradiation hardening of F/M steel. There is an interaction between the two elements. C-Cr has a strong synergistic mechanism, which will cause serious hardening when the content is higher than 0.05% and the Cr content is higher than 10%. Cr-Si has a strong antagonistic mechanism, which can achieve the comprehensive irradiation hardening effect in the 9Cr-0.8Si combination. N-Mn needs N controlled lower than 0.01%. Mo-W needs to control Mo content higher than 0.5% to alleviate irradiation hardening. There is a weak synergistic effect in Si-V; when the content is between 0.3% and 0.8% and the V content is between 0.2% and 0.3%, it can assist in optimizing the composition of F/M steel. Through the optimization of multi-element combination, the composition of F/M steel with lower irradiation hardening can be designed.