Hard Domains Research Articles

Cryogenic strength-ductility mechanism of heterostructured CoCrFeMnNi high-entropy alloy

A typical heterogeneous structure with ultrafine grains embedded in coarse grains is obtained by partial recrystallization annealing, which exhibits excellent cryogenic mechanical properties. Researches reveal that the hard domains, high-density GND pile-ups, and multi-axial stress states of heterogeneous structures provide nucleation positions and critical stresses for triggering twinning, meanwhile, nanotwins can refine the hard domain grains to improve the heterogeneity of heterogeneous structures during cryogenic plastic deformation. Therefore, the heterostructure-twinning interaction is identified as the key factor in realizing the excellent cryogenic strength-ductility synergy of the heterostructured CoCrFeMnNi high-entropy alloy. Besides, the nucleation and propagation of generous microcracks at single-order twin boundaries induced by the excellent twinning activity result in the rapid fracture of the heterostructured samples, whereas the microcracks can hardly be observed nearby high-order nanotwins, which indicates that generating more high-order nanotwins is a promising guiding scheme to prepare the heterostructured materials with superior cryogenic mechanical properties.

Microstructure evolution from homogeneous as-cast state to annealed heterogeneous structure and mechanical properties of Al-Zn-Mg-Cu alloys with trace TiB2 particles

Materials with a final heterogeneous structure (HS) possess an excellent combination of strength and ductility. However, fine and homogeneous grains are desired in as-cast ingots to avoid defects. The evolution from an as-cast homogeneous microstructure to a pronounced HS owing to the trace addition of TiB2 particles was studied in Al-Zn-Mg-Cu alloys with traditional thermomechanical treatment. It is revealed that the triple junctions and over 2 μm precipitates co-located with TiB2 enhance the particle-stimulated nucleation of recrystallization. The dislocation density difference between the recrystallized and recovered grains is further enhanced by cold rolling. A pronounced HS with alternating soft and hard domains accompanied by multimodal precipitates is modulated, realizing a synergy of yield strength as 632.4 MPa and elongation as 8.8%. It is confirmed that the HS, rather than precipitates, is the primary source of geometrically necessary dislocations (GNDs), leading to the synergy of strength and ductility. Atomistic simulations on the deformation behavior of HS were used to elucidate the strain partition and role of GNDs on mechanical properties. Our results provide a convenient route to fabricate heterogeneous Al-Zn-Mg-Cu alloy by trace addition of ceramic particles in ingots casting instead of elaborated controlling of deformation processing.

Room temperature self-healing and reprocessing elastomer with dynamic bonds for flexible wearable sensor

The production of room-temperature (RT) self-healing elastomers with good mechanical properties is significant for application in soft electronics, yet remains a challenge in material design. Herein, we present an effective and feasible approach to create RT self-healing cross-linked elastomers (CEs) through photo-initiated copolymerization. A key feature is the incorporation of 2,7-dihydroxynaphthalene and alicyclic diisocyanate into the polymer backbone as hard domains, along with the rational optimization of the soft segments. In addition, urethane-based H-bonding interactions, acting as sacrificial bond, contribute to the high toughness of the CEs. The resulting CEs exhibit desirable mechanical performances, including a tensile strength of 12.9 MPa, an elongation at break of approximately 1243 %, and a high toughness of 68.64 MJ m–3. Furthermore, by integrating a flexible PTMEG-based polymeric chain and hindered urea bonds into the backbone, the chain mobility and dynamic nature of the CEs are improved. The CEs are capable of reprocessing and self-healing at RT within 30 min upon scratching, with a self-healing efficiency in toughness reaching 99.64 %. The dynamic networks are evidenced by rheological test, stress relaxation analysis, as well as creep and recovery experiments. These CEs, characterized by their superior properties, hold promise for applications in flexible wearable electronics.

Reducing defects in hard carbon graphite domain: Employing a fully dynamic bonding with a multi-crosslinked biomass-based binder for enhanced sodium ion storage

Binders are crucial for maintaining the integrity of an electrode and are confronted with the imperative for multifunctionality. Herein, we have developed and synthesized an entirely biomass-based water-soluble binder with outstanding adhesion, conductivity, flowability, and dispersibility for the hard carbon (HC) anode. Specifically, MXene (Ti3C2Tx) reduces the amount of HC graphite domain imperfections, the cross-linked carboxymethyl chitosan (CCS) chain facilitates Na+ movement, and the amphiphilic nature of lignosulfonate (LS) enhances the distribution of active material. As a result, the HC anode achieves an initial coulombic efficiency (ICE) of 88 % and high-capacity retention of 110 % after 100 cycles. This work promotes the progress of green energy in parallel with the promotion of the high-value utilization of biomass.

Effect of martensite hardness on mechanical properties and stress/strain-partitioning behavior in ferrite + martensite dual-phase steels

Low-carbon dual-phase (DP) steels composed of ferrite and martensite are widely used in automotive industries due to their good combination of strength and ductility and remarkable strain-hardening ability. Such exceptional mechanical properties of DP steels arise from microstructural deformation heterogeneity due to the different deformation roles of soft ferrite and hard martensite. The present study investigated mechanical properties and local deformation behavior of DP steels having different martensite hardness (strength) using digital image correlation (DIC) technique and in-situ X-ray diffraction (XRD) experiment during tensile deformation. The martensite hardness was reduced by tempering treatment, and its mechanical properties were compared with the as-quenched DP specimen by tensile testing. The tempered DP specimen exhibited reduced strength but enhanced ductility, especially in post-uniform elongation, compared to the as-quenched DP specimen. DIC-strain analysis indicated that the tempering effectively inhibited strain localization, allowing a greater contribution of martensite to plastic deformation. On the other hand, the in-situ XRD analysis revealed that the tempering significantly restricted the stress-increasing potential of martensite. Our results suggest that martensite, acting as a hard domain, plays a significant role in enhancing strain-hardening ability and achieving large uniform elongation due to its high stress-increasing potential. However, the presence of hard martensite also imposes restrictions on post-uniform elongation due to the strong strain localization induced in microstructures.

Grafting of nonpolar polyisoprene as midblock and polar polylactide as outer block onto cellulose to produce bio-based thermoplastic elastomers

Sustainable cellulose-graft-diblock copolymers (cellulose-graft-polyisoprene-block-polylactide, MCC-g-PI-b-PLLA, MCC was chemically-modified microcrystalline cellulose) were designed and delicately synthesized for the first time by a mild and facile procedure via combining ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization techniques, which conquered the difficulties in synthesis due to the distinct chemical properties among the MCC backbone, PI and PLLA blocks. Two separate glass transition temperatures were detected for MCC-g-PI-b-PLLA copolymers by differential scanning calorimetry, indicative of microphase separation, consistent with small-angle X-ray scattering and atomic force microscopy measurements. The α-form crystals of PLLA outer blocks were revealed by wide-angle X-ray diffraction measurement. The monotonic and step-cyclic tensile tests revealed that the mechanical property could be tuned by changing the molecular mass of PI midblock. The two ends of the soft PI midblock were anchored by rigid cellulose backbone and hard PLLA outer block, respectively, which served as physical crosslinking points. The rigid cellulose backbones brought the PI rubbery domains and PLLA hard domains together to form a whole hierarchical microstructure, endowing the copolymers with distinguished mechanical property. This work provided a feasible approach to producing environmental-friendly cellulose-based copolymers with fully biomass-derived feedstocks, having a profound impact on the development of sustainable polymer-based materials.

Hierarchical ferrous medium entropy with heterogeneous precipitates embedded in core-shell grain structure for superior mechanical properties

Superalloys designed for high-temperature applications, featuring a face-centered cubic matrix and L12 precipitates, have shown excellent tensile properties at both room and elevated temperatures. However, the substantial Ni and Co, necessary for generating a high fraction of the ordered L12 phase within the matrix, results in high mass density and cost, subsequently limiting their widespread industrial application. It is important to increase Fe content over Ni and Co while preserving outstanding mechanical properties at ambient and high temperatures. In this study, we propose a novel approach to introduce a hierarchical structure in a 60-at%-Fe-based medium entropy alloy. The heterogeneous nano-precipitates embedded in harmonic (core-shell) grain structure reinforce mechanical contrast between soft and hard domains, achieving an excellent heterostructure. The present alloy incorporates hierarchical heterogeneity at multi-scales, combining heterogeneous grain at micrometers, precipitates at tens of nanometers, and elemental fluctuation at nanometers. This hierarchical structure shows superior mechanical properties at room and high temperatures comparable to those of conventional superalloys. Further, the high content of Fe in this alloy system shows excellent performance in alloy cost and mass density. This work suggests the unique hierarchical heterostructure to overcome the trade-off dilemma in alloy cost, mass density, and mechanical properties in room/elevated temperatures.

Multiphase hydrogen bonding strategies room temperature self-healing, recyclable polyurethane elastomers for applications in flame retardant materials

Novel elastomers offer new opportunities to develop multifunctional materials in terms of combining mechanical strength, room-temperature self-healing properties and recyclability. However, self-healing polymers have high mechanical strength at high internal cross-linking density, but restrict the movement of molecular chain segments leading to reduced self-healing efficiency. The presence of microphase-separated structures makes the polymers poorly efficient for repair at room temperature. In this paper, a multiphase hydrogen bonding (H-bonding) strategy is used to introduce an aliphatic ring into the system to form a repeating unit with the hard segments, as well as a bis-benzene ring structure with a methylene linkage to disrupt the crystallization of the hard domains. Specifically, PUPI-M2I3 has a mechanical tensile strength of 17.93 MPa, an excellent tensile ratio of 1109.88 %, the sample can recover 95.93 % at room temperature after 24 h of fracture and stretching, with excellent room temperature self-healing performance and recyclability. Meanwhile, the self-healing flame-retardant material based on PUPI-M2I3 is developed by comprehensive consideration, which opens a new way for the research and development of flame-retardant materials.

The Hydrogen Bonding in the Hard Domains of the Siloxane Polyurea Copolymer Elastomers.

For probing the structure-property relationships of the polyurea elastomers, we synthesize the siloxane polyurea copolymer elastomer by using two aminopropyl-terminated polysiloxane monomers with low and high number-average molecular weight (Mn), i.e., L-30D and H-130D. To study the influence of the copolymer structures on the film properties, these films are analyzed to obtain the tensile performance, UV-vis spectra, cross-sectional topographies, and glass transition temperature (Tg). The two synthetic thermoplastic elastomer films are characterized by transparency, ductility, and the Tg of the hard domains, depending on the reacting compositions. Furthermore, the film elasticity behavior is studied by the strain recovery and cyclic tensile test, and then, the linear fitting of the tensile data is used to describe the film elasticity based on the Mooney-Rivlin model. Moreover, the temperature-dependent infrared (IR) spectra during heating and cooling are conducted to study the strength and recovery rate of the hydrogen bonding, respectively, and their influence on the film performance is further analyzed; the calculated Mn of the hard segment chains is correlated to the macroscopic recovery rate of the hydrogen bonding. These results can add deep insight to the structure-property relationships of the siloxane polyurea copolymer.

The robustness waterproof ionogel based on the phase separation to form soft hard heterostructures and the interaction of cation-π realizes underwater adhesion and sensing

Flexible ionic conductors hold significant promise for advancing the field of soft ion electronics in the future. However, the creation of flexible conductors that possess mechanical robustness, underwater adhesion and underwater motion monitoring remains a challenge. Drawing inspiration from the multiphase hetero structure found in biological connective tissues, such as high modulus fibers and low modulus water-rich matrices, this article proposes a one-pot polymerization in-situ design strategy to create a hydrophobic ionogel with a hetero structure of soft and hard domains. The mechanical robustness, elasticity, and toughness of the ionogel are achieved through a synergistic combination of a strong skeleton in the hard domain and an elastic matrix in the soft domain. Additionally,hydrophobic aromatic rings and quaternary ammonium cation simulated cation-π interactions in mussel foot silk protein. Upon contact with water, the hydrophobic clusters quickly aggregate, facilitating the expulsion of interfacial water and exposing salicylic acid groups and quaternary ammonium cationic groups, leading to outstanding underwater adhesion between the ionogel and various substrates. The resulting hydrophobic ionogel can be utilized in underwater wearable electronic devices for monitoring human movement and physiological information, underwater repair monitoring, and intelligent soft robotics, demonstrating its vast potential in the field of underwater sensors.

Mechanically customizable lignin bio-elastomers based on tailorable multiscale microstructures

The development of bio-based polyurethanes (PU) elastomers with well-designed multiscale microstructures to customize their mechanical performances was desired, but remained an ongoing challenge. Herein, a novel strategy of integrating tailorable hard-soft nanophases with multiple hydrogen bond (H-bond) interactions was proposed to construct mechanically customizable PU bio-elastomers. In this strategy, highly reactive lignin with high hydroxyl contents was employed as bio-polyol monomer reacting with hexamethylene diisocyanate (HDI) to construct carbamate bonds with a function of tailoring H-bond degree via altering the feeding ratio of lignin. The rigid lignin cooperating with HDI as hard segments self-assembled to generate phase separated nanostructures. Consequently, the integration of well-defined hard-soft nanophases and multiple H-bond interactions in the synthesized lignin-based PU (LPU) achieved excellent and customizable mechanical performances ranging from highly elastic rubber to highly stiff plastic with ultrahigh strength of 72.8 MPa and unprecedented modulus of 3.5 GPa. Impressively, rubber-like LPU elastomers could recover 90 % of initial stress even after 500 stretching cycles, indicating fascinating resilience and fatigue resistance. More especially, rigid LPU plastics with fully hard domains and dense H-bond networks could be transformed into flexible and bendable paper-like elastomers once eliminating intermolecular H-bond interactions under 60 °C hot water. Thus, this work provides a feasible and promising approach to construct supramolecular PU elastomers with excellent and customizable mechanical performances to extend their on-demand applications.

Highly tough, crack‐resistant and self‐healable piezo‐ionic skin enabled by dynamic hard domains with mechanosensitive ionic channel

AbstractRobust and reliable piezo‐ionic materials that are both crack resistant and self‐healable like biological skin hold great promise for applications inflexible electronics and intelligent systems with prolonged service lives. However, such a combination of high toughness, superior crack resistance, autonomous self‐healing and effective control of ion dynamics is rarely seen in artificial iontronic skin because these features are seemingly incompatible in materials design. Here, we resolve this perennial mismatch through a molecularly engineered strategy of implanting carboxyl‐functionalized groups into the dynamic hard domain structure of synthesized poly(urethane‐urea). This design provides an ultra‐high fracture energy of 211.27 kJ m−2 that is over 123.54 times that of tough human skin, while maintaining skin‐like stretchability, elasticity, and autonomous self‐healing with a 96.40% healing efficiency. Moreover, the carboxyl anion group allows the dynamic confinement of ionic fluids though electrostatic interaction, thereby ensuring a remarkable pressure sensitivity of 7.03 kPa−1 for the tactile sensors. As such, we successfully demonstrated the enormous potential ability of this skin‐like piezo‐ionic sensor for biomedical monitoring and robotic item identification, which indicates promising future uses in flexible electronics and human–machine interactions.

Construction of CO2‐based thermoplastic elastomer via combining aliphatic polycarbonate and polyamide: A multiblock copolymer PPC‐mb‐PA6

AbstractA CO2‐based thermoplastic elastomer, poly(propylene carbonate)‐multiblock‐polyamide6 (PPC‐mb‐PA6) copolymer, was constructed through coupling amorphous/soft PPC blocks with crystalline/hard PA6 blocks. The PPC‐mb‐PA6 copolymers with different block length pairs were designed and synthesized, and then fully characterized by structural, thermal, and mechanical analysis. The proton nuclear magnetic resonance (1H‐NMR), diffusion ordered spectroscopy (DOSY), heteronuclear multiple‐bond correlation (HMBC) and gel permeation chromatography (GPC) results confirm that the multiblock sequence structure of PPC‐mb‐PA6. The differential scanning calorimetry (DSC) tests show that all PPC‐mb‐PA6s possess melting points around 179–206°C. The thermal and mechanical analysis indicates improved service temperatures (T5% up to 270°C) and tensile strength ranging from 15.8 to 39.6 MPa with higher PA6 content. The dynamic mechanical analysis demonstrates excellent shape memory effect of PPC‐mb‐PA6 with thermal stimuli responsiveness derived from the micro phase separation between soft PPC and hard PA6 domains. And the characteristic strain fixity parameter (Rf) and deformation recovery rate (Rr) are 98% and 100%, respectively, which are comparable with other excellent shape memory polymers.

Gender, Intraparty Competition, and the Substantive Focus of Parliamentary Questions in South Africa

Extant research suggests that women ask more parliamentary questions (PQs) on soft policy domains while their male peers focus on hard domains, which are arguably more relevant. This study contributes to this body of research by examining how electoral incentives shape intraparty politics, and specifically the substantive focus of PQs. It argues that women’s focus on soft policy domains is not constant, with variations found in situations where intraparty competition is high. Female MPs will have fewer incentives to focus on soft policy domains if they are electorally vulnerable and as elections draw closer. The mechanism is clear: Women face strong bias in parliament, which means they need to work harder to stand on an equal footing with their male counterparts. As a result, rather than shying away from competition, they will try to maximize their career prospects by shifting their attention to (hard) policy domains that are considered more important to both parties and voters. These claims are tested in the case of South Africa, drawing upon a novel dataset of PQs from 2006 to 2023. South Africa is an interesting case study as it is one of the most feminized parliaments in Africa and has strong electoral incentives for intraparty competition. The findings confirm most theoretical expectations and clarify the electoral and gender-related predispositions that drive the substantive focus of questions.

Low cycle fatigue properties of CoCrFeNiMn high-entropy alloy with heterogeneous microstructure

Heterogeneous microstructure is a hot topic in materials science which facilitates tackling the dilemma of strength-ductility trade-off in engineering materials including high-entropy alloys. The present investigation was conducted on the impact of different microstructures including heterogeneous microstructure, constructed by thermomechanical treatment including cold rolling followed by annealing, on the monotonic and cyclic behavior of a CoCrFeNiMn high-entropy alloy. The tailored microstructure contained three features: non-recrystallized as a hard domain, ultrafine-recrystallized, and fine-recrystallized regions. A desirable combination of strength and ductility including UTS of ∼1.1 GPa together with an elongation of ∼15 % was achieved due to benefiting from hetero-deformation-induced hardening and activation of deformation twins in the fine recrystallized grains. Regarding low-cycle fatigue behavior, at the strain amplitude of 0.4 %, heterogeneous microstructure exhibits remarkable fatigue properties, including high maximum stress and extraordinary lifetime (more than 2 × 105). The compelling reasons for these desirable properties are triggering deformation twins in fine recrystallized grain, the absence of brittle sigma phase as a good location of crack initiation, and the non-recrystallized area as a hard domain for suppressing crack propagation. The results suggested that the heterogeneous microstructure has significant benefits during applying low strain amplitude, however, at high strain amplitude, grain refinement is not recommended, and coarse-grained microstructure provides better properties. The present investigation is a step forward to understand the significance of heterogeneous microstructures to improve fatigue properties of high- or medium-entropy alloys.

A novel strategy for design of mechanically robust antifouling coatings via bifunctional domain engineering

The issue of biofouling on marine structures carries significant economic and ecological implications, necessitating the development of effective and durable antifouling coatings. Traditional organic antifouling coatings often struggle with mechanical robustness in harsh marine environments, making them fragile and highly susceptible to abrasion. To address these challenges, we propose a novel “bifunctional domain engineering” strategy for designing robust antifouling coatings that combines excellent mechanical strength of a Fe-based amorphous layer and high antifouling efficacy of an incorporated organics. The hard domains consist of Fe-based amorphous micro humps, providing a sturdy framework that enhances the coating's mechanical durability. In contrast, the soft domains comprise epoxy resin infused with Cu2O and 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), offering a dual-action antifouling function via controllable antifouling agent release. Evaluation of antifouling performance by lab tests against Pseudomonas aeruginosa, Staphylococcus aureus, and Chlorella algae and practical marine field tests (for 150 days) demonstrates significant reductions in bacterial and algal adhesion (nearly 100 % resistance) with the bifunctional domain engineered coating (referred to as HSR coating), compared to pure amorphous coating. Mechanical durability tests, including abrasion and erosion experiments, underscore the HSR coating's excellent wear resistance. Importantly, the HSR coating maintains its outstanding antifouling properties even after 1000 abrasion cycles, highlighting its potential for long-term marine applications in harsh conditions. This study lays the groundwork for design of robust antifouling coatings capable of withstanding the harsh operating environments while effectively combating biofouling.

Synergistic mechanism of hetero-structured Al–Mg–Si–Cu–Zn–Fe–Mn alloys with greatly enhanced strength, ductility and formability

Al–Mg–Si alloy sheets applied in automobile industry are required to possess good formability, high strength and ductility. Herein, our results show that a heterogeneous cellular microstructure, i.e., soft domains embedded in hard domains, can be readily attained via a short-flow processing route with concomitant improvement in the strength (YS: 177–184 MPa, UTS: 317–328 MPa), elongation (25.7%–27.3 %) and formability (r‾= 0.771, Δr = 0.047) of pre-aged alloy. The distribution of recrystallization grains, texture and coupled soft/hard domains in the Al–Mg–Si–Cu–Zn–Fe–Mn alloys and the effect on mechanical properties have been investigated. Moreover, the formation and synergistic action mechanisms of coupled soft/hard domains were put forward in this work.

Adhesive and healable supramolecular comb-polymers

A series of supramolecular comb polymers (SCPs) with adhesive and healable characteristics have been generated through the copolymerisation of methacrylate monomers featuring aromatic amide functionalities with lauryl methacrylate. By varying the amide functionality and loading of the supramolecular monomers, the properties of the resulting SCPs can be tailored, ultimately providing stable films at room temperature. As the loading of the amide-bearing monomer was increased, the phase separation between the hard and soft domains was enhanced, promoting larger hard-domain aggregation, as observed via atomic force microscopy (AFM). The mechanical properties of the SCPs correlated to the loading of the amide-bearing monomers, by increasing the mol% incorporation the resulting SCPs transition from possessing high strain to high ultimate tensile strength (UTS) and Young's modulus (YM). Over several re-adhesion cycles, the SCPs were shown to retain their shear strength when thermally adhered to both glass and aluminium substrates. Additionally, the SCPs exhibited healable properties at elevated temperatures (> 45 °C) allowing for the recovery of mechanical properties post-damage.

Shear bands and interface-affected-zone enabled high strength and ductility in heterogeneous laminate-Cu

The rapid development of shear bands (SBs) in nanocrystalline Cu is prone to lead to structural failure, while coarse crystalline Cu with high strain hardening capacity can effectively inhibit the growth of SBs. Heterogeneous laminate (HL) has a structure of alternating soft and hard domains, which dramatically increases ductility while reducing strength loss. In this work, molecular dynamics (MD) simulations revealed how SBs in the HL-Cu during the stable plastic flow stage (the applied strain of 10 ∼ 20 %) strengthen the material. It is suggested that when SBs are uniformly and densely distributed in the structure, the strain gradient strengthening effect in the neighboring regions is significantly increased. Moreover, the efficiency of strain hardening can be maximized when the width of the interface-affected-zone (Defined as the region where a significant linear change in strain occurs, i.e., a strain gradient exists, located at the junction of the soft and hard domains.) caused by the uneven distribution of geometrically necessary dislocations (GNDs) is exactly the same as the layer thickness. The results show that the strength of HL can be increased by more than 14 % by reducing the layer thickness by half.

Synergetic softening-strengthening behaviors of gradient nano-grained CoCrFeMnNi high-entropy alloys located in the inverse Hall-Petch range revealed by atomistic simulations

Gradient-structured CoCrFeMnNi high-entropy alloy (HEA) with all grain sizes lying in the inverse Hall-Petch range exhibits a significant synergistic softening behavior, with the yield strength even lower than the rule of mixtures (ROM) under uniaxial tensile loading. The softening of grain boundaries (GB) is very pronounced in hard domains due to the extremely small grain size. Moreover, the coordinated deformation of heterostructure promotes grain rotation in soft domains with large grain sizes. However, the extra strength generated by hetero-deformation induced (HDI) strengthening increases with increasing volume fraction of hard domain, contributing to a gradual decrease in the gap between yield strength and ROM. Here, we identify multiple deformation mechanisms promoted by mechanical incompatibility through molecular dynamics (MD) simulations. On the one hand, the higher volume fraction of the hard domain encourages the adaptation of dislocation-mediated activities to plastic strains, thus reducing the possibility of GB sliding or intergranular brittle cracking. More importantly, soft domains are more susceptible to detwinning under additional compressive stress, which induces grain refinement in localized regions and contributes extra strength. Observation of the strain distribution reveals that the banded shear bands (SBs) are spread throughout the soft domains, which effectively improves strain gradient strengthening. It has been verified that the gradient structure has the highest extra strength at the hard domain volume fraction of 40–50%. The findings provide insights into the engineering applications of gradient-structured HEA.