Effective thermal management in high-power electronics demands materials that simultaneously exhibit high thermal conductivity, mechanical strength, and stable coefficient of thermal expansion (CTE). In this work, an interpenetrating Cu/CuCr alloy architecture was developed to address this challenge. The design features a percolating Cu skeleton providing uninterrupted electronic pathways for superior thermal transport, while the CuCr matrix delivers structural integrity and dimensional stability. Crucially, graphene layers were incorporated at the interface to suppress elemental interdiffusion, thereby preserving uninterrupted electronic transport pathways in the percolating Cu skeleton. Consequently, the interpenetrating Cu/CuCr10 composite achieves a tensile strength of 502 MPa, thermal conductivity of 330 W·m−1·K−1 at 25 °C, and stable CTE of 14.5 ppm·K−1 (25–200 °C). The thermal conductivity exhibits a minimal reduction of 2.4% over 25–200 °C, and at 200 °C, it remains 12.7% higher than that of CuCr10. The reaction between graphene layers and Cr was also investigated, which forms Cr7C3 particles and effectively enhances interface bonding. This work establishes a generalizable strategy for designing advanced thermal management materials with co-optimized high heat dissipation and long-term reliability.
The effects of Cr content (4 and 6 at. %) on the microstructural evolution and interdiffusion behavior of γ'/γ, γ'/γ', and γ'/γ+γ' diffusion couples at 1050 °C, 1100 °C, and 1150 °C were systematically studied. Results indicated that the addition of Cr can reduce the average effective Al interdiffusion coefficient, and a higher Cr content, a lower average effective Al interdiffusion coefficient. In the γ'/γ diffusion couple, Al exhibited the lowest diffusion activation energy, corresponding to the highest average effective interdiffusion coefficient. In contrast, the diffusion activation energy of Al showed an opposite trend in the γ'/γ' and γ'/γ + γ' diffusion couples. Meanwhile, the addition of 6 at. % Cr accelerated the interdiffusion between the γ' and γ + γ' alloy, inducing the formation of dotted-like and needle-like TCP phases enriched with Cr, Mo, W, and Re, which increases the hardness on the γ + γ' side near the original interface.
NiW750 alloy is a high-density structural material for high-load and impact-resistant applications; however, achieving superior mechanical properties requires strategies to simultaneously improve its strength and ductility. Here, a solution treatment–ultrasonic shot peening (USP)–aging route is employed to construct a fourfold-composite gradient nanostructure (GNS) in a forged NiW750 alloy. After optimization of the processing parameters, the alloy with a GNS layer ~500 μm thick achieves an excellent strength–ductility combination, exhibiting a surface hardness, ultimate tensile strength, yield strength, and elongation of 595.5 ± 6.3 HV1, 1618.3 ± 21.9 MPa, 1157.0 ± 8.5 MPa, and 31.8 ± 2.9%, respectively. The formation mechanism of the GNS is elucidated. USP produces a triple-composite GNS layer consisting of gradient nanograins (GNG), gradient nanotwins (GNT), and gradient dislocation structures (GDS), owing to the transfer and attenuation of impact energy from the surface toward the interior. Subsequent peak aging introduces gradient nanoprecipitation (GNP), facilitated by the depth-dependent diffusion pathways and nucleation sites provided by the triple-composite GNS for Ni₄W precipitation. The strength enhancement of the fourfold-composite GNS alloy is quantitatively evaluated by considering the contributions from Ni4W nanoprecipitates, dislocations, grain boundaries, and twin boundaries using a thickness-weighted calculation that accounts for depth-dependent microstructural variations. The retained ductility is attributed to the combined effects of a ductile fine-grained core, strain accommodation mediated by the fourfold gradient structure, twin-assisted strain hardening, and interactions between nanoprecipitates and deformation defects. This work provides a fourfold-GNS design strategy and processing route for manufacturing high-strength and ductile Ni–W-based alloys.
The impact that a variation in stress state has on key microscopic deformation aspects leading to fracture (including: Transformation Induced Plasticity (TRIP) kinetics, microstrain partitioning between phases and damage evolution) in a 3rd generation Medium Mn (med-Mn) steel is presented. This investigation was carried out using unnotched, misaligned, shallowly and severely notched tensile specimens which enabled a range of stress states to be tested. Highly resolved TRIP kinetics for these different geometries was delineated using High Energy X-ray Diffraction, in which the fastest and slowest transformation of austenite-to-martensite was exhibited by the severely and misaligned notched specimens, respectively. Furthermore, a unique, one-time electropolishing micro-speckle patterning methodology to enable sufficient Electron Backscatter Diffraction (EBSD) phase indexing and microscale Digital Image Correlation (μDIC) is introduced in this work. Quasi in-situ Scanning Electron Microscope tests coupled with EBSD and μDIC revealed the polygonal ferrite and tempered martensitic regions to be considerably more sensitive to changes in the steel's global stress state compared its initial austenite/eventually transformed martensitic regions. Furthermore, just before fracture for all specimen designs, similar void area fractions were revealed indicating that a critical void size triggers an exponential raise in coalescence and then fracture. Ultimately, this work encourages further development of experimental and software techniques to understand the complex interplay of TRIP, microstrain partitioning, and damage evolution in 3G TRIP-assisted steels under diverse stress states.
To address the critical demand for lightweight and high-strength materials for energy conservation and emission reduction, this study presents a novel composite process of “high-energy ball milling-powder forging-rolling-annealing” to fabricate a high-performance Al-5 Mg alloy. This route enables mechanical alloying and nanostructuring, producing a metastable microstructure characterized by a supersaturated solid solution, high-density dislocations, and stacking faults. Subsequent deformation and annealing result in a uniform ultrafine-grained structure with average grain sizes of 0.40 μm (forged) and 0.83 μm (rolled and annealed). A key finding is the phase transformation pathway regulated by the synergistic effect of intense deformation and mechanochemical reaction. Notably, no β-Al₃Mg₂ constituent particles are detected throughout the processing; instead, dispersed nano sized MgO particles are formed in situ. Multi scale characterization further confirms the presence of multiple defects, including high dislocation densities and dispersed nano MgO, which collectively contribute to an enhanced strengthening synergy. As a result, the alloy exhibits exceptional mechanical properties: tensile strengths of ∼692 MPa (forged) and ∼698 MPa (rolled and annealed) - far exceeding those of conventional Al-5 Mg alloys - while the rolled-annealed condition also provides improved ductility. This work demonstrates that microstructural and phase engineering via process innovation offers an efficient and industrially viable pathway for developing high strength AlMg alloys.
The rapid development of advanced industries has placed increasingly stringent demands on the heat resistance of hot-work tool steels. In this study, submicron Ti(C,N) particles were added into H13 steel fabricated by laser powder bed fusion (LPBF), and the effects of their addition on microstructural evolution and heat-resistant performance were investigated. Simulation shows that the submicron Ti(C,N) particles dissolve during heating in the LPBF process, and nanometer-scale (Ti,V)(C,N) particles form during cooling. This effect of submicron Ti(C,N) particle addition on the microstructure of LPBF H13 steel markedly reduces its temper-softening susceptibility, increases its high-temperature strength retention and resistance to deformation softening at elevated temperatures. The enhancement of heat resistance originates from multiple microstructural effects. They include suppressing the transformation of VC into (Mo,V)6C by Ti and N atoms, retarding dislocation recovery and martensitic lath coarsening and pinning the boundaries of dynamically recrystallized grains by the (Ti,V)(C,N) nanoparticles, and lowering the nucleation rate of Cr23C6 and (Mo,V)6C particles by formation of (Ti,V)(C,N). In addition, the refinement of prior austenite grains and the reduced number density of coarse Cr23C6 and (Mo,V)6C particles alleviate microvoid accumulation during tensile deformation at 600 °C, resulting in improved ductility. These findings provide important guidance for designing ceramic particle modified LPBF H13 steel with superior heat resistance.
The interactions of hydrides with dislocations and tension twins influence local strain accommodation in hydrogenated titanium. In this study, these interactions were investigated in commercially pure titanium during tensile deformation using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In the grains examined, prismatic slip bands displayed two distinct responses at hydride/matrix interfaces, including local accumulation near the interfaces and partial transmission from the matrix into the hydrides. These responses depended on crystallographic geometry, with slip trace nearly parallel to the hydride interface favoring dislocation accumulation and more inclined slip trace facilitating slip transfer. In addition, a secondary low-Schmid-factor prismatic slip system was also observed near grain-boundary hydrides, further illustrating the influence of hydrides on local deformation. Hydrides also played a dual role in {101¯2} tension twin. Hydride interfaces appeared to favor twin nucleation, while the local twin narrowing observed at some hydride-twin intersections suggests that hydrides may constrain twin propagation and thickening. These findings reveal the mechanisms governing hydride-dislocation and hydride-twin interactions and provide insight into local strain accommodation in hydrogenated titanium.
This study systematically presents new insights into the grain size on the microstructure and mechanical properties of 4 N2 high-purity iron through a combination of controlled heat treatments, microstructural characterization, and room-temperature tensile testing. Three distinct grain sizes of 4 N2 high-purity irons (Grade 6: 61 ± 2 μm, Grade 3: 180 ± 2 μm, Grade 2: 249 ± 2 μm) were produced. Microstructural analysis revealed that the recrystallization texture evolved from a mix of α and γ fibers to a dominant {110} 〈001〉 texture accompanied by a weaker {113} <141> component with increasing grain size. Tensile tests at strain rates ranging from 1 × 10−4 s−1 to 1 × 10−2 s−1 showed that strength is enhanced by both grain refinement and a higher strain rate. Fine-grained specimens exhibited discontinuous yielding, while the coarse-grained specimens presented continuous yielding at lower strain rates. The sensitivity of yield strength to strain rate increased with grain size. In the annealed state, the dislocation density decreased with increasing grain size. However, after deformation, it increased significantly—particularly in finer grains and at higher strain rates. This resulted in refined dislocation substructures and enhanced dislocation tangling. Analysis of strengthening mechanisms identified dislocation strengthening as the primary contributor, with its effect amplified by grain refinement and higher strain rates.
Effects of coatings and Ru on fatigue behavior in Ni-base single crystal superalloy were experimentally investigated using two kinds of superalloys (third generation Ni-base single crystal superalloy and fourth generation Ni-base single crystal superalloy) and coatings (MCrAlY coating and PtAl coating). Rotating bending fatigue tests were conducted at high temperature (900 °C) and under fully reversed conditions (R = -1). A complex-stress-field fatigue failure model accounting for stress distribution and crack nucleation in rotating bending fatigue is established in this work. For all Ni-base single crystal superalloys with different coatings, the crack initiation site and crack propagation path have been identified during the fatigue test. By means of scanning electron microscopy (SEM) and transmission electron microscope (TEM), the modifications on fatigue fracture mechanisms caused by coatings and Ru are evidenced. The enhancement of oxidation resistance by the addition of coatings effectively reduces the amounts of crack initiation sites and promotes to the crack closure, while new crack propagation paths are provided by the element interdiffusion between coatings and substrate. The amounts of topological close-packed (TCP) phases precipitated in interdiffusion zone (IDZ) and the width of IDZ deflect crack propagation along new pathways, leading to different fatigue fracture modes, which are apparently reflected at the morphologies of fractures and fatigue striations on the surface of fractures. The diffusion of Ru from substrate to coatings modifies the whole process of fatigue fracture, including the crack initiation, crack growth, and the final fracture.
The morphology of Fe-rich intermetallics in Al-7Si-0.3 Mg-0.25Fe alloys is highly susceptible to various impurity elements. To eliminate these interferences and evaluate the intrinsic modification potential of Sn, its effect on the evolution of Fe-rich phases was systematically investigated. Quantitative microstructural analysis reveals that Sn addition not only decreases the size and area fraction of both α-Al15Fe3Si2 and π-Al8FeMg3Si6 phases, but also triggers the precipitation of a novel spheroidal phase. Advanced characterizations utilizing EPMA and HRTEM verify that this newly formed phase exhibits a complex multi-layered core-shell architecture composed of multiple grains. Furthermore, by combining nanoscale observations with thermodynamic calculations, the formation mechanism of this unique structure was systematically elucidated. Crucially, it is revealed that this core-shell architecture is governed by a multi-stage non-equilibrium solidification and solid-state precipitation mechanism. A fine-grained α-Al15Fe3Si2 core initially forms via burst nucleation, trapping supersaturated Si. Upon in-situ solid-state precipitation of the trapped Si, the fine α-Al15Fe3Si2 grains act as a structural skeleton, intimately intertwining with the nano-Si to construct a unique composite network. Concurrently, driven by one-dimensional anisotropic coherent matching, the Mg2Sn phase selectively adsorbs onto the existing substrates, forming a compact encapsulating shell. This physical isolation fundamentally suppresses the detrimental transformation of the Fe-rich core into the brittle π-Al8FeMg3Si6 phase. This study unravels the novel solid-state precipitation and anisotropic adsorption pathways of spheroidal phases, offering a solid theoretical and experimental basis for the morphology control and microstructure optimization of brittle Fe-rich phases in cast aluminum alloys.
Improving the performance of alloys fabricated by additive manufacturing (AM) through a simple process based on the existing composition is a topic of great interest. In this study, we proposed a strategy of doping oxidized powder to improve the strength and ductility of Ti-Zr-V-Nb-Al lightweight refractory high-entropy alloy (LRHEA) fabricated by direct energy deposition (DED), a typical AM method, and systematically investigated the effects of the oxidation degree of doping oxidized powder on the microstructure and mechanical properties of the AM sample. The results show that the oxygen from the oxidized powders was uniformly dissolved in the sample fabricated by doping 50 wt% medium-oxidized powders (oxygen content is 0.32 wt%). The oxygen promoted the formation of local chemical ordering (LCO), increasing its content from 3.6 ± 0.5% to 10.1 ± 1.1%. The yield strength and elongation of the sample increased from 855 ± 11 MPa and 16 ± 1.6% to 1023 ± 15 MPa and 26.7 ± 2.1%, respectively. The increase in strength is mainly attributed to the strengthening effects of interstitial oxygen and LCO, while the improved ductility is attributed to the development of secondary slip bands induced by LCO and the extensive formation of kink bands, which enhance the uniform deformation capability of the alloy. In contrast, although doping 50 wt% highly-oxidized powder (oxygen content is 0.64 wt%) further increased the yield strength of the sample (1105 ± 21 MPa), significantly reducing the elongation of the sample to 0.8 ± 0.4% owing to the excessively high oxygen content and the formation of defects. This study provides new insights and processes strategies for improving the performance of alloys fabricated by AM.
Solution-treatment temperature plays a key role in controlling the γ/γ' microstructural evolution of Ni₃Al-based single-crystal superalloys. Reliable quantitative characterization of this evolution remains challenging because γ' precipitates are often irregular, locally connected, and accompanied by blurred γ/γ' interfaces in scanning electron microscopy (SEM) micrographs. In this study, a U-Net++ model was enhanced by introducing region–center–offset (RCO) supervision, and the resulting U-Net++–RCO model was used for γ' phase segmentation in SEM micrographs obtained under different solution-treatment conditions. It achieved the highest segmentation performance in the present dataset, with precision, recall, Dice, and IoU values of 0.968, 0.940, 0.954, and 0.912, respectively, and showed stable performance in five-fold image-level cross-validation. The accuracy of quantitative feature was further evaluated at both image and region levels, and quality-controlled masks were used for final quantitative analysis. After validating segmentation and feature extraction, the developed workflow was used to quantify γ/γ' morphological changes at different solution-treatment temperatures. After the common first-stage treatment at 1300 °C for 4 h, increasing the second-stage solution-treatment temperature from 1310 to 1330 °C was associated with progressive γ' dissolution. Primary γ' precipitates in primary dendrite regions appeared to be largely dissolved around 1320 °C in the analyzed regions, whereas primary γ' precipitates in secondary dendrite arm regions appeared to persist to higher temperatures. The area fraction and size of interdendritic coarse primary γ' precipitates progressively decreased, and these precipitates were not observed at 1330 °C in the analyzed images. This work establishes a deep-learning-assisted workflow for efficient batch segmentation with quality control, quantitative feature extraction, and analysis of γ/γ' microstructural evolution during solution treatment.
This study employed neutron diffraction, combined with conventional microstructural characterization and mechanical testing methods, to systematically elucidate the microstructure evolution, residual stress distribution and mechanical properties of local dry underwater welded SUS304. Compared with the onshore weldment, LDUW refined grains to 23.43 μm and formed a microstructure of 70.6% recrystallized grains and abundant LAGBs by rapid cooling. The δ → γ phase transformation was suppressed during solidification, leading to an increase in δ-ferrite content to 4.55%, compared to only 1.00% in the onshore weldment. Furthermore, highly asymmetrical residual stress distributions were generated by LDUW, with longitudinal tensile stress peaking at 347 MPa. Correspondingly, the LDUW weldments exhibited inferior tensile performance, with an average ultimate tensile strength of 658 ± 14.4 MPa and an average elongation of 29.0 ± 0.7%, which was lower than the on-land weldments (776.9 ± 16.4 MPa and 33.0 ± 0.7%). Owing to inhomogeneous microstructures and complex residual stress distribution, the martensitic transformation of underwater weldments was restricted during tensile deformation, which ultimately made the overall mechanical properties of underwater weldments inferior to those of onshore weldments. This work offers practical guidance for tailoring the microstructure and mechanical properties of underwater weldments and optimizing their welding processes.
The wear and corrosion performance of high-entropy alloy (HEA) coatings depends not only on phase constitution but also on the morphology, spatial distribution, and characteristic size of hard phases. Nevertheless, the mechanism underlying Mo-triggered phase evolution in reconciling wear resistance and corrosion resistance remains unclear within high-entropy alloy coating systems. In this work, gradient Mo-containing HEA coatings were fabricated on AISI 304 stainless steel via laser cladding, and the effects of Mo addition on microstructure evolution, tribological behavior and electrochemical properties were systematically investigated. The results reveal that increasing Mo content induces a microstructure transition from single-phase FCC to FCC + lamellar eutectic, blocky semi-continuous σ phase, and coarsened hypereutectic structure. The Mo0.6 coating possesses a nanoscale lamellar dual-phase microstructure, which weakens microgalvanic corrosion, yielding a corrosion current density of merely 6.9 μA·cm−2 in sulfuric acid solution. The Mo0.8 coating generates multi-scale σ phases with a hardness of 945.08 HV0.2, which is 4.3 times that of the Mo-free coating; its wear rate is reduced by one order of magnitude, delivering the optimal wear resistance. Excessive Mo promotes the formation of a continuous brittle σ-phase network, triggering interfacial cracks and simultaneously deteriorating wear performance. XPS results verify that Mo4+/Mo6+ species cooperate with Cr2O3 to construct a compact passive film. This study clarifies the differentiated regulation mechanism of σ-phase morphology on wear and corrosion resistance, and provides guidance for the microstructure design of eutectic high-entropy protective coatings.
Phosphorus (P) is a primary tramp element in scrap-based steelmaking, necessitating precise characterization of its microstructural distribution to mitigate its detrimental effects and enable the design of high-quality sustainable steels. In this study, we investigate the nanoscale distribution of P across a range of P-alloyed steels using atom probe tomography (APT). We identify and rationalize the crystallography-dependent field evaporation artifacts from the P in body-centered cubic iron solid solution. The P distributions and Fe charge-state-ratio maps, together with the calculated bulk bond energies, show certain correlation with temporary P retention and crystallography-modulated surface redistribution, although the underlying migration pathway requires further clarification. We also examined localized P enrichment associated with Ti/C-rich clusters, a C-rich carbide-like region, and candidate planar interfaces. These observations demonstrate that APT can distinguish localized P heterogeneity from crystallography-associated artifacts, although the structural identity of the interfaces requires independent confirmation. These results provide a methodological foundation for interpreting P distributions, enabling microstructural engineering and upcycling of tramp-element-rich steels.
Achieving high-strength 7075-T6 Al alloy welded joints with balanced ductility remains difficult due to weld-zone softening, heterogeneous precipitation and deformation localization. In this study, a TiC-assisted welding route was combined with a novel double-solution and multi-stage aging heat treatment process, termed DS-MA, to restore microstructural and mechanical compatibility. Submicron TiC particles refined and stabilized the fusion region during heat treatment, while DS-MA reconstructed the precipitation structure by promoting fine intragranular precipitates and reducing grain-boundary heterogeneity. After DS-MA, the fusion line and fusion zone retained fine equiaxed grains of 11.3 μm and 10.1 μm, respectively. The average precipitate size in the fusion zone decreased to 6.5 ± 0.3 nm, the TEM-measured projected precipitate area fraction increased to 25.3 ± 0.9%, and the PFZ width narrowed to 28.6 ± 0.4 nm. Consequently, the joint achieved a yield strength of 486.2 MPa, tensile strength of 570.3 MPa and elongation of 15.6%. CPFEM results indicate that the refined and dense precipitate distribution reduces local stress concentration and promotes a more uniform plastic-strain distribution. These results demonstrate that TiC-stabilized DS-MA is an effective post-weld processing strategy for improving the strength–ductility synergy of 7xxx-series Al alloy joints.
Mg-Al-Ca alloys offer balanced thermal and mechanical properties, with Mn additions improving corrosion resistance and strength through Al-Mn intermetallic formation. While prior studies emphasize property enhancement, limited work addresses their precipitation crystallography and growth. This study investigates Al8Mn5 nanoprecipitates in Mg-4.5Al-2.5Ca-xMn (x = 0.02, 0.1 at.%) alloys using TEM and APT. The heat-treated eutectic microstructure comprises α-Mg grains (with Al8Mn5 and C15 precipitates), and C36/C14 Laves phases. Key findings include: (1) faceted morphology with growth ledges at 63¯3¯0faces ∥Mg11¯00 interfaces, (2) inhibition of C15 plate growth along112¯0 in the Mg basal plane, and (3) Ca segregation at the interface of Al8Mn5/α-Mg.
