CoCrNi-based multi-principal element alloys (MPEAs) with face-centered cubic (FCC) structure are known for their exceptional tensile ductility and fracture toughness. However, their insufficient strength limits practical engineering applications. To overcome this limitation, this study develops an integrated strategy combining machine learning (ML) trained on thermodynamic simulation data with multi-objective optimization for compositional design. The approach aims to achieve a high gamma ' phase volume fraction, high solvus temperature, and a high-entropy matrix, while suppressing the formation of detrimental precipitates. Key optimization criteria include the gamma ' phase volume fraction, solvus temperature, topologically close-packed (TCP) phase content, and matrix mixing entropy, with the goal of synergistically enhancing mechanical properties. An optimized composition, Co23.3Cr17.4Ni48.1Al6.1Ti5.1 (at.%), was identified and experimentally validated. The resulting alloy in the as-cast state exhibits an outstanding balance of strength and ductility, demonstrating a yield strength of 786 +/- 15 MPa, an ultimate tensile strength of 1049 +/- 6 MPa, and an elongation of 25 +/- 2%. This ML and multi-objective optimization-based material design strategy not only enables efficient discovery of target compositions for gamma '-strengthened CoCrNi-based MPEAs but also offers a novel pathway for advanced alloy development.

This study designed and developed a potential Ni43Co28Cr7.9Al10Fe5Ti2Ta2Mo1Nb1B0.1 (at.%) high-entropy superalloy. A heterogeneous, partially recrystallized microstructure is achieved via thermomechanical processing. Primary blocky and secondary spherical L1(2) precipitates form in high density in both the recrystallized and non-recrystallized regions. These L1(2) precipitates reach a volume fraction of up to similar to 67% and are identified as the multi-component (Ni,Co)(3)(Al,Ti,Ta,Nb) phase. At room temperature, the alloy exhibits a high yield strength of similar to 1003 MPa, an ultimate tensile strength of similar to 1533 MPa, and a good ductility of similar to 17.0 %. The yield strength continuously decreases with increasing temperature from room temperature to 900 degrees C, and its mechanical properties are superior to those of most conventional superalloys and high-entropy alloys. Strengthening is primarily attributed to two mechanisms: precipitation strengthening and dislocation strengthening. The dominant deformation mechanisms involve dislocation slip and the formation of stacking faults. Furthermore, the observations of the side-surface morphologies reveal a dual role for the NR regions. At room temperature, the high dislocation density within these regions enhances strength, whereas at elevated temperatures, they help to maintain ductility. This unique dual functionality, coupled with the absence of grain boundaries in the NR regions, facilitates plastic deformation and mitigates intermediate-temperature embrittlement. In summary, the design strategy of heterogeneous-structured superalloy with high-fraction L1(2) precipitates provides valuable insight for developing novel high-entropy superalloys with superior properties.

Accurate prediction of both the Widmansta & uml;tten start (Ws) temperature and the transformation stasis requires a quantitative description of the energy barrier governing the growth of Widmansta & uml;tten ferrite. In this study, a concise model is developed by explicitly distinguishing the energy barriers associated with lengthening and thickening. The model adopts the lengthening barrier attributed to curvature and strain energies, and further incorporates the thickening barrier caused by strain energy, together with the diffusional dissipation of substitutional solute. The Ws temperature is predicted by the condition under which the energy barriers for both lengthening and thickening can be overcome, while transformation stasis occurs when the thickening barrier becomes insurmountable due to progressive carbon enrichment of untransformed austenite. The new model enables accurate prediction of the Ws temperatures across Fe-xC and Fe-0.1C-xMn/Ni/Si/Cr/Mo systems and the carbon enrichment in austenite at stasis in Fe-C-Mn and Fe-C-Mn-Si alloys.

In this work, corrosion dynamics of TaTiZr amorphous medium-entropy alloy (AMEA) coated 15-15Ti austenitic stainless steel were investigated in liquid lead-bismuth eutectic (LBE) with an oxygen concentration of 5×10−7 wt.% for 500–1500 h at 550°C. Compared to bare steel, the coated sample unexpectedly exhibited inferior corrosion resistance. It is attributed to the cracking and peeling off of the coating due to the large coefficient of thermal expansion mismatch stress, which allows inward penetration of LBE. Owing to the high oxygen affinity of TaTiZr coating, the penetrated LBE contains insufficient oxygen content to facilitate the formation of protective oxide scales on teel surface, giving rise to severe dissolution corrosion, with depth of corrosion increasing over time. However, TaTiZr coating maintained a stable amorphous structure without phase transformation or consumption, though it showed noticeable thickening due to the dissolution of massive oxygen. Our findings are expected to promote understanding of potential failure of AMEA coated claddings in LBE.

The microstructure of drop-cast Co31.5 Fe18.5 Ni31.5 Al18.5 eutectic high-entropy alloy (EHEA) consists of twophase eutectic dendrites and eutectic cells. Within the eutectic dendrites/cells, the two-phase eutectic primarily displays a lamellar structure consisting of NiAl phase (BCC) and CoFeNi phase (FCC). The dropcast Co31.5 Fe18.5 Ni31.5 Al18.5 EHEA exhibits a moderate yield strength of 599 f 5 MPa with an acceptable ductility of 7.8% f 0.4%. Thermo-mechanical processing, specifically cold rolling and annealing (CRA), is employed to enhance the mechanical properties of the drop-cast EHEA. Following CRA treatment, partial recrystallization occurs within both the BCC and FCC phases. Notably, the FCC phase exhibits a higher degree of recrystallization compared to the BCC phase. Thus, the CRA EHEA is regarded as a dual heterostructured material, achieving a high yield strength of similar to 1231 f8 MPa while retaining acceptable ductility (7.8% f 0.3%). Subsequent analysis of tensile deformation behavior, including fracture surface morphology, side-surface observations and deformation substructure, reveals pronounced plastic deformation in the FCC phase, while the BCC phase exhibits rare deformation. Subsequently, the strengthening mechanisms are systematically analyzed from two distinct perspectives. Firstly, the high strength of CRA EHEA is mainly attributed to dislocation strengthening, precipitation strengthening, grain-boundary strengthening and interface strengthening. In particular, the investigation of FCC individual phase property is novel and meaningful, providing critical insights into the understanding of the strengthening mechanism. From another perspective, the high strength of the CRA EHEA can be attributed to hetero-deformation-induced (HDI) stress strengthening. In conclusion, this paper will provide the implications for microstructural optimization and mechanical property improvement of EHEAs. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Accurate prediction of dislocation density in bainitic steels remains challenging due to limited experimental data and the lack of reliable physical models. In this study, a hybrid framework integrating machine learning with a physical model is proposed. Within this framework, multi-layer perceptron (MLP) is employed to predict the lath thickness of bainitic ferrite as an intermediate variable that links alloy composition and transformation temperature with dislocation density through a parameter-free energy-balance model. The proposed framework enables accurate prediction of the dependence of dislocation density on transformation temperature in both carbide-free bainitic steels and nanobainitic steels. This method enables rapid microstructure prediction for alloy design of bainitic steels.

The 9Cr3W3Co heat-resistant steel used in ultra-supercritical power plants needs to work for a long time under high temperature and high stress, so studying its long-term stress rupture behavior is of great significance. Stress rupture tests at temperatures of 600∼675°C and stresses of 89∼260 MPa were conducted, then the constituent phase, microstructure evolution, fracture morphology and mechanism were researched. As temperature and stress increase, the stress rupture life gradually shortens. At high temperatures, the atomic diffusion rate accelerates and the precipitated phases gradually grow and merge, leading to weakening of the precipitation strengthening effect. Under high stress, dislocations slip causes a decrease in dislocation density, thereby reducing the hindering effect on martensitic interface migration. Then grain deformation, recovery and recrystallization occur, resulting in a reduction in stress rupture life. At all temperatures and stresses, 9Cr3W3Co steel exhibits ductile fracture, cracks mainly nucleate near the precipitated phase and propagate along grain boundaries. At the same temperature, the higher the stress, the greater the number of ductile dimples and the smaller their size.

9Cr3W3Co heat-resistant steel has become a widely used material for key components in advanced ultrasupercritical thermal power units due to its excellent high-temperature properties and corrosion resistance. In this study, the steel was subjected to aging treatment at different temperatures and times, then the microstructure and mechanical properties were investigated. After long-term aging, Laves phase forms along martensite lath boundaries and prior austenite boundaries. With increasing aging time and temperature, the width of martensite lath and the size of M23C6 carbides increase. The Laves phase particles grow from 0.210 mu m to 0.351 mu m, and their morphology changes from regular short-rod shapes to irregular ones. The coarsening rate of Laves phase reaches a maximum at 630 degrees C. Moreover, hardness exhibits a slight decrease with increasing aging temperature and time. Plasticity, strength, and the growth and aggregation of precipitates all influence the impact properties. After 20,000 h of aging, both yield strength and elongation remain at relatively high levels, with impact energy values all exceeding 20 J. After 30,000 h of aging, the coarsening of precipitates has a more pronounced effect on impact toughness. In summary, 9Cr3W3Co heat-resistant steel maintains high stabilities of microstructure and property after long-term exposure at high temperature.

Inclusion-reinforcement has been used as a pivotal strategy in advancing the mechanical properties of metal alloys. In the framework of chemical complexity of inclusions from traditional chemically homogeneous precipitates to chemically complex multicomponent intermetallic compounds, this review outlines the structural characteristics and deformation mechanisms of concentrated multicomponent alloys compared with traditional precipitate-strengthened dilute alloys, distinguishing between coherent and noncoherent precipitate strengthening. Coherent precipitates leverage slip continuity with the matrix, simultaneously act as both dislocation sources and obstacles, resulting in a self-hardening mechanism to achieve outstanding synergy of strength-ductility. In contrast, noncoherent precipitates, in addition to acting as obstacles to dislocation glide, they induce severe stress concentrations and even interfacial cracking, causing progressive strain localization and contributing to the strength–ductility trade-off. Emphasis is placed on the matrix-precipitate-composition design of complex multicomponent alloys and the deformation mechanism-mechanical properties-strengthening mechanisms of single-phase FCC multicomponent alloys. Furthermore, the precipitate strengthening of concentrated multicomponent alloys are elaborated with a focus on both coherent and noncoherent ductile multicomponent inclusions. In spite of their advantages, this review also emphasizes the challenges, limitations, and emerging perspectives for pushing the bounds for next-generation concentrated multicomponent alloys.

In this paper, we developed a novel Co40Ni37Cr16Ti7 medium-entropy alloy (MEA) exhibiting a unique triplex-phase "FCC + L1(2) + eta" microstructure. The microstructure of the alloy can be tailored through thermomechanical processing. The microstructure resulting from the cold rolling and single-step or two-step low-temperature annealing treatment (CA-700, CA-800 and CAA) is categorized into shear band regions and non-shear band regions. The non-shear band regions predominantly consist of lamellar precipitates (eta) with sparse short rod-like precipitates (eta), whereas the shear-band regions exhibit a reversed morphology dominated by short rod-like precipitates. Simultaneously, a dispersion of fine spherical L1(2) precipitates are formed in both regions. The CA-700, CA-800, and CAA alloys exhibit poor ductility owing to the extensive formation of brittle eta-phase precipitates. In contrast, the high-temperature recrystallized CRA alloy develops equiaxed grains with fine lamellar eta precipitates preferentially distributed along grain boundaries. Concurrently, a high density of near-spherical L1(2) nano-precipitates is uniformly distributed within the grain interiors, leading to an excellent strength-ductility synergy. The CRA alloy achieves a yield strength of similar to 1082 MPa, an ultimate tensile strength of similar to 1493 MPa, and a ductility of similar to 22.4 %. The high strength of the CRA alloy is predominantly attributed to precipitation strengthening, with the uniformly dispersed L1(2) nano-precipitates (volume fraction: similar to 49 %) acting as potent barriers to dislocation motion. Furthermore, the CRA alloy maintains remarkable ductility through a deformation mode involving dense slip traces and stacking faults (SFs), which promote homogeneous plastic deformation. This unique combination of strengthening and deformation mechanisms results in the observed excellent strength-ductility synergy.

In this study, we present a Co2Ni2Cr medium-entropy alloy (MEA) co-doped with Al/Mo, and systematically regulate its microstructure through thermo-mechanical processing. A representative (Co2Ni2Cr)88Al8Mo4 MEA, fabricated via cold rolling followed by annealing at 765 degrees C, exhibits an excellent strength-ductility synergy. It achieves a high yield strength of -1150 MPa, an ultimate tensile strength of -1397 MPa, and maintains a good ductility of -17 %. The representative MEA undergoes partial recrystallization, with high-density L12 nanoparticles uniformly distributed in both recrystallized and non-recrystallized regions. Furthermore, EBSD analysis reveals the presence of high-density dislocations within the non-recrystallized region. Therefore, precipitation strengthening by L12 nanoparticles and dislocation strengthening are likely the primary mechanisms contributing to the high yield strength observed in the representative MEA. Simultaneously, its excellent ductility can be attributed to the highly coherent two-phase interface, the presence of high-density microbands and Lomer-Cottrell (LC) locks, as well as a certain proportion of recrystallized regions. Therefore, this study presents an effective design strategy to achieve an excellent strength-ductility synergy in a MEA through optimized thermo-mechanical processing.

The HCP alpha-precipitates in duplex titanium (Ti) alloys are quite important to their mechanical properties in terms of accommodating plastic deformation for large ductility on the one hand and hindering dislocation motion for high strength by alpha-precipitate/beta-matrix interfaces on the other hand. However, the intrinsic limited slip systems of low symmetric alpha-precipitates lead to progressive deformation localization even cracking due to high stress concentrations, becoming the origin of the strength-ductility conflict in Ti alloys. Here, a tri-modal Ti-4.5Al-4.5Mo-7V-1.5Cr-1.5Zr (wt.%) alloy as a model is decorated by hierarchically multi-scaled and multi-polymorphic alpha precipitates to introduce multiple plasticity mechanisms for high strength-ductility synergy. The sequentially-activated plasticity mechanisms (SAPMs) dominantly involve prismatic < a > and pyramidal < c + a > dislocation slip and cross-slip in globular micron-alpha(g), the P-type HCP-to-FCC transformation and stacking faults/nanotwins in rod-like submicron-alpha(r), and prismatic < a > dislocation slip transfer in secondary nano-alpha(s). The SAPMs in the alpha precipitates are strongly size-dependent and explained in terms of the critical resolved shear stress (CRSS). The contribution of multi-polymorphic alpha-precipitates to the yield strength is quantified with their distinguished strengthening capabilities of alpha-precipitates in multi-scales. The present hierarchical Ti alloy with the tri-modal microstructure achieves a good combination of yield/ultimate tensile strength of 1550/1614 MPa and ductility of similar to 8.7 %.

In-situ fatigue crack growth tests are conducted on laser powder bed fused TiC/Ti6Al4V composites under a stress ratio of 0, utilizing digital image correlation and characterization techniques to monitor crack evolution. As a result, the major crack exhibits a microscopically sinuous zigzag path, resulting from the growth and coalescence of microcracks governed by localized shear stress. Owing to microstructural barriers such as prior beta grain boundaries, the propagation of microstructurally small crack with a length of less than 200 mu m exhibits notable discontinuity and retardation. In contrast, an acceleration in crack growth rate is observed along the alpha phase boundaries within individual grains, indicating a path of reduced resistance. Compared to the long crack, the physically small crack shows larger near-tip deformation and smaller plastic zone size, attributed to the reduced crack closure effect. The existence of fatigue steps, secondary small cracks, local fatigue striations, and pore defects further confirms the influence of microstructure on crack growth behavior.

In response to the increased demand for service reliability of industrial gas turbine (IGT) blades, the compression deformation behavior of three Ni-based single crystal superalloys with different Re additions (0Re, 1.5Re and 3Re, in wt%) from room temperature to 980 degrees C was studied. The microstructure evolution of alloys was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the strength at low temperature (<= 760 degrees C) of the three alloys has little difference, but the strength at high temperature increases with the increase of Re content. Further microstructure characterization shows that the distribution of Re elements in gamma-phase promotes the formation of uniform and dense interfacial dislocation network, and at the same time prevents the dislocations from cutting gamma '-phase and inhibits the formation of SFs (stacking faults). In addition, the segregation of Re at SFs can stabilize the surrounding dislocation network and increase the SFE (stacking faults energy) of gamma '-phase. The further calculation results show that the elastic constants of Ni3Al increase regardless of whether Re occupies the Ni position or the Al position, which is the result of Ni3Al strengthened with Re. This study will provide experimental support for further elucidating the Re effect and help to optimize the composition design of IGT blades.

Cyclic reliability, a key indicator of a material's mechanical stability under cyclic loading, is inherently tied to fatigue performance. Precipitation-strengthened high-strength Al alloys typically undergo significant cyclic softening under asymmetric stress cycles with a positive mean stress, thereby inducing premature fatigue failure. Here, we report a high-strength Al alloy engineered with a dual-gradient architecture, featuring both subgrains and nanoprecipitates, which displays remarkable resistance to cyclic softening, resulting in a nearly two-orderof-magnitude enhancement in fatigue life. This superior cyclic stability stems from the rapid dynamic hardening response and high mechanical energy dissipation intrinsic to this gradient subgrain-nanoprecipitate structure. Specifically, the synergistic interaction between the subgrain network and graded precipitate distribution reconfigures dislocation behavior from cross-slip to planar slip, while fragmenting dislocations into fine slip units. These unique interactions facilitate stable cyclic hardening and high internal damping. Consequently, strain localization is effectively suppressed, and both crack initiation and propagation are significantly delayed. This composite gradient strategy provides a novel paradigm for designing fatigue-resistant Al alloys.

Adding alloying elements to binary nitrides enables the design of hard and tough coatings. To improve the mechanical and tribological performances of TiN-based coatings, La atoms were added to TiAlN coatings to form TiAlLaN coatings. Magnetron sputtering was conducted to prepare the TiAlLaN coatings. Thereafter, scanning electron microscopy (SEM), x-ray diffraction (XRD), nano-indentation, and a tribometer were utilized to test their microstructure, phases, and mechanical and tribological performances. Next, this study analyzed how lanthanum affected the microstructure and tribological performances of the TiAlLaN coatings. Incorporating La atoms in TiAlN coatings reduced the crystallite size and enhanced the coating toughness and hardness. The hardness H and elastic modulus E of the TiAlLaN coatings first increased and then decreased with the increase in La. Meanwhile, the coatings had improved wear and friction properties. The increased H/E and H3/E2 levels, which have been considered to reflect the hard coating’s toughness, were acquired based on the TiAlLaN coating, possessing enhanced hardness (19.8 GPa). The coefficient of friction and the wear rates of the coatings reduced and then increased with the increase in La. The TiAlLaN coating with 1.4 % of lanthanum had the lowest friction coefficient and wear rate of around 0.383 and 1.59 × 10−8 mm3/N·m, respectively, corresponding to a higher H/E (~0.086) and H3/E2 (~0.147 GPa). Adding an appropriate amount of La can substantially enhance the TiAlN coating’s tribological and mechanical properties. The TiAlLaN coating with remarkable characteristics may be applied to a steel substrate.

While face-centered cubic (FCC) CoCrNi-series multi-principal element alloys (MPEAs) exhibit outstanding tensile plasticity and fracture toughness, their insufficient strength limits industrial applications. Here, we report a novel strategy to overcome this limitation through trace boron (B) microalloying in non-equimolar Co1.6Cr1.2Ni3.4Al0.8 (Co22.9Cr17.1Ni48.6Al11.4, at.%). Adding merely 0.1 mole fraction of B (Co22.9Cr17.1Ni47.1Al11.4B1.4, at.%) refines the average grain size by approximately 63% (from 457.4 to 166.7 μm). Remarkably, room-temperature (RT) tensile testing reveals a simultaneous enhancement of both strength and ductility: the yield strength increases from 406.9MPa to 574.7MPa, while the elongation rises from 8.6% to 21.7%. This strength-ductility synergy originates from three interconnected mechanisms: (1) Segregation of B at the grain boundaries (GBs), which reduces brittle σ phases formation. (2) The synergistic interaction between M5B3-borides and discontinuous precipitate γ′ phases promotes the formation of curved GBs, which effectively retards crack initiation. (3) The Hall-Petch effect resulting from grain refinement. These findings establish a microalloying-based strategy to achieve strength-ductility synergy in CoCrNi-series MPEAs.

The CoCrFeNi-series high entropy alloys (HEAs) with face-centered cubic (FCC) structure generally exhibit exceptional tensile ductility and fracture toughness, but the insufficient strength limits their practical engi-neering application. In this study, the (CoCrFeNi)94Ti2Al4 (at. %) HEA was prepared by the liquid-nitrogen rolling, followed by partial recrystallization and aging heat treatments to obtain the multi-scale heterogeneous microstructure consisting of heterogeneous grain size, precipitates, and grain defects. By constructing the het-erogeneous microstructure, (CoCrFeNi)94Ti2Al4 HEA exhibits the yield and ultimate tensile strength of-1 and 1.2 GPa, respectively, accompanied by a uniform elongation of-21 %. The exceptional strength and ductility synergy can be attributed to the hetero-deformation induced (HDI) strengthening and hardening effects, as evidenced by the microstructural observation and load-unload-reload (LUR) tensile tests.