Superior Combination Research Articles

Cooperative Multiagent Reinforcement Learning Coupled With A* Search for Ship Multicabin Equipment Layout Considering Pipe Route

_ The paper presents a novel approach of cooperative multiagent reinforcement learning (CMARL) combined with A* search to address ship multicabin equipment layout considering pipe route, aiming to minimize pipe cost while considering practical requirements. The formulation is established through equipment simplification and grid marking, and A* search is utilized to value the pipe route. By designing equipment states, the equipment layout in each cabin is solved using a CMARL approach that involves three actions. Subsequently, comparative experiments were conducted on an engine room case by CMARL against genetic algorithm and single multiagent reinforcement learning methods under the condition of coupling with A* search. The parameter values for these methods were sampled using Latin Hypercube. The findings demonstrate that CMARL has superior combination properties. Keywords ship equipment layout; multicabin layout; cooperative multiagent reinforcement learning; A* search; pipe route

Mechanical Performance of Copper-Nanocluster-Polymer Nanolattices.

A type of copper-nanocluster-polymer composites is reported and showcased that their 3D nanolattices exhibit a superior combination of high strength, toughness, deformability, resilience, and damage-tolerance. Notably, the strength and toughness of ultralight copper-nanocluster-polymer nanolattices in some cases surpass current best performers, including alumina, nickel, and other ceramic or metallic lattices at low densities. Additionally, copper-nanocluster-polymer nanolattices are super-resilient, crack-resistant, and one-step printed under ambient condition which can be easily integrated into sophisticated microsystems as highly effective internal protectors. The findings suggest that, unlike traditional nanocomposites, the laser-induced interface and the high fraction of ultrasmall Cu15 nanoclusters as crosslinking junctions contribute to the marked nonlinear elasticity of copper-nanocluster-polymer network, which synergizes with the lattice-topology effect and culminates in the exceptional mechanical performance.

Enhancing strength–ductility synergy of AlNp/Al composite by regulating heterostructure of matrix grain and particle distribution

Three heterostructured AlNp/Al composites with different microstructure configurations were fabricated by liquid–solid reaction combined with subsequent thermal-mechanical treatment to obtain a superior strength and ductility combination. The effects of the microstructure configuration including the AlN particle distribution and matrix grain structure on the tensile strength and ductility were studied in detail. The results show that the simultaneous enhancement of tensile strength and ductility can be achieved. The Uniformed-AlNp/Al composite with relatively dispersed particles exhibits a superior ultimate tensile strength of ~387 MPa with an elongation to failure of ~9.1%. It shows an outstanding specific tensile strength and elongation combination compared with other reported particle reinforced aluminum matrix composites. Furthermore, the hetero-deformation induced (HDI) stress has been calculated and is shown to increase significantly in the Uniformed-AlNp/Al composite. It is revealed that the HDI stress plays a crucial role in the significant enhancement of strength and ductility for the AlNp/Al composite.

An innovative strategy to prepare fine-grained Mg-Al alloys with a superior strength-ductility synergy via wire-arc directed energy deposition

Fine grain structures are necessary in obtaining superior mechanical properties of Mg alloys fabricated by wire-arc directed energy deposition (DED), which is still challenging nowadays. In the present work, a novel strategy by the synergistic effect of arc oscillation and feeding of SiC particles (SiCps), i.e., WADED-OS, has been proposed, which is extremely effective in grain refinement of the AZ31 thin-wall component. The average grain size of the WADED-OS AZ31 thin-wall component (∼19 μm) decreases by ∼81% compared to the counterpart fabricated via conventional straight deposition (∼102.4 μm). Introducing arc oscillation can reduce the temperature gradient in the molten pool, which promotes the transition from columnar grains to equiaxed grains. At the same time, the incorporation of SiCps can decrease the average grain size due to the heterogeneous nucleation and grain growth inhibition effects. The thin-wall component produced via the novel WADED-OS strategy exhibits a superior combination of strength and ductility, i.e., the ultimate tensile strength and elongation are 265 ± 2 MPa and 19.8 ± 2.3% along the deposition direction, respectively. This study proposes an innovative strategy for achieving wire-arc DED Mg alloy components with fine microstructures and superior mechanical properties.

Enhancement of strength and ductile-brittle transition temperature of SA508 Gr.3 low-alloy steel by controlling heat accumulation in laser powder-directed energy deposition

The safety and longevity of small modular reactors are affected by reactor pressure vessels, which are complex integral components made of SA508 Gr.3 low-alloy steel. In this study, the impacts of heat accumulation on the microstructural and mechanical characteristics (tensile properties and Charpy V-notched impact energy) of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated. Rectangular samples were prepared using long raster and short raster scanning strategies for changing heat buildup, and the mechanical tests were conducted depending on build direction. The time-temperature profile measured at a fixed point in the long raster sample showed a lower maximum temperature and a higher cooling rate, indicating lower heat accumulation compared to that of the short raster sample. In each build direction, the yield strength of the long raster sample was 45.8 %–60.5 % higher and its ductile-brittle transition temperature was 76.8–103.8 °C lower than that of the short raster sample. Additionally, compared to conventionally made samples and without requiring heat treatment, the long raster sample exhibited over a 45 % increase in yield strength and a 22.7 °C reduction in the ductile-brittle transition temperature. The superior combination in long raster samples is induced by smaller effective grain size, smaller cementite, and a higher pre-existing dislocation density. The results emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.

Abstract 3915: BMS-986442 (AGEN1777), a novel TIGIT/CD96 bispecific antibody, demonstrates superior monotherapy and combination activity versus conventional anti-TIGIT antibodies in preclinical models

Abstract TIGIT immune checkpoint blockade can enhance anti-tumor immunity, however conventional anti-TIGIT antibodies have shown suboptimal activity in the clinic. Here, we present the first preclinical disclosure of BMS-986442 (AGEN1777), a novel and fully human Fc-enhanced bispecific antibody against TIGIT and CD96 co-receptor, that demonstrates superior pharmacological activity compared to conventional TIGIT monospecific antibodies (mAbs). Gene expression of TIGIT, CD96, and the co-stimulatory counter-receptor CD226 in tumor samples from patients with cancer was identified using bulk and single cell RNA-sequencing. To target this interaction, Fc-engineered knob-in-hole bispecific antibodies against TIGIT and CD96 were developed and affinity optimized to achieve potent and complete blockade of TIGIT and CD96 ligand interactions. BMS-986442 and corresponding monospecific anti-TIGIT and anti-CD96 monoclonal antibodies were evaluated with or without anti-PD-1 in a variety of human T and NK cell stimulation assays. Mouse surrogate TIGIT/CD96 bispecific antibodies were developed and evaluated as monotherapy or together with anti-PD-1 in colorectal CT26 and breast orthotopic 4T1 tumor bearing mice. In CT26 and 4T1 tumor-bearing mouse models, the Fc-enhanced TIGIT/CD96 bispecific antibody demonstrated superior tumor control compared to either anti-TIGIT, anti-CD96, or the combination of anti-TIGIT and anti-CD96 mAbs. Tumor control was dependent on co-engaging activating Fcγ receptors, as an Fc-silent bispecific antibody lacked anti-tumor activity. In the tumor microenvironment, efficacy was associated with increased frequency of CD226+ effector and TCF-1+ GrzB- memory precursor CD8 T cells, increased frequency and activation of cytotoxic NK cells, and increased activation of professional APCs, including B cells, MHC Class II monocytes, and dendritic cells as determined by expression of CD40, CD83, and CD86. In primary human in vitro assays, BMS-986442 potently enhanced T cell responsiveness and activation compared with conventional anti-TIGIT mAbs alone and in combination with anti-PD-1 (nivolumab). Lastly, BMS-986442 promoted superior NK cell activation in tumor co-culture assays. In conclusion, BMS-986442 demonstrated a differentiated FcγR-dependent mechanism-of-action to enhance innate and adaptive immune responses compared with anti-TIGIT or anti-CD96 mAbs. BMS-986442 is currently advancing in phase I clinical studies in patients with advanced solid cancers (NCT05543629). Citation Format: Rebecca Ward, Nicola Ramsay, Spencer Campbell, Hema Patel, Mark Bushell, Benjamin M. Morin, Beth Wensley, David A. Savitsky, Pilar Garcia-Broncano, Bishnu Joshi, Emmanuel Briend, Olga Ignatovich, Zahra Jawad, Nils-Petter Rudqvist, Nicholas Wilson, Dhan Chand. BMS-986442 (AGEN1777), a novel TIGIT/CD96 bispecific antibody, demonstrates superior monotherapy and combination activity versus conventional anti-TIGIT antibodies in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3915.

Manipulating A2/B2 microstructure via adjusting Al/Ni ratio in cost-effective Fe-based AlNiFeCr alloys for controllable strength-plasticity combination

Cost-effective Fe-based Al-Cr-Fe-Ni alloys were prepared by arc melting process, and Al/Ni ratio in AlxNi(40-x)Fe40Cr20 (0 ≤ x ≤ 40, at.%) alloys was adjusted for superior mechanical properties. With increasing x, the initial FCC phase diminishes and A2/B2 phase is promoted. Two typical A2/B2 structures are observed, one consists of spherical/cuboidal B2 nanoparticles distributed in A2 matrix (denoted as AMBP), and the other consists of ellipsoidal and plate-like A2 particles distributed in B2 matrix (denoted as BMAP). The fraction of AMBP domains decreases while that of BMAP increases with increasing x, which is harder with lowered plasticity/toughness, accompanied with some micro-cracks propagating along the plate-like A2/B2 interfaces in BMAP domains. The alloy shows the best strength-plasticity combination at x = 15 with >95 vol% AMBP domains. This study suggests a cost-effective Al15Ni25Fe40Cr20 medium-entropy alloy with superior strength-plasticity combination. The Al15Ni25Fe40Cr20 alloy per metric ton is 13% and 18% cheaper than well-known equiatomic AlCrFeNi alloy and AlCrFe2Ni2 alloy, respectively.

Movement Strategy Influences on the Characteristics of Low-Carbon Steel Generated by the Lamination Object Manufacturing Method

This paper investigates the effects of heating movement techniques on the properties of low-carbon steel samples that are 3D printed using S20C lamination object manufacturing (LOM). A Tungsten iner gas (TIG) machine and a computer numerical control (CNC) machine were used together to join the steel sheet. The LOM samples were created with a straight-profile, short-profile, cross-profile, and curved-profile. The results indicate that the majority of the samples had a grain size number of 7–9. The samples exhibited an isotropy grain shape. The LOM samples exhibited dimples, which suggests ductility fractures. Pore flaws showed up in the microstructure of the cross-profile and short-profile samples during the LOM process. The samples with curved- and straight-profiles had a better microstructure. In comparison to samples with a short profile and a cross-profile, the samples with a straight-profile and a curved-profile had a superior combination of ultimate tensile strengths (UTSs) and elongation value. The straight- and curved-profiles’ greater elongation and tensile strength can be attributed to their improved microstructure and finer grain size. A straight-profile sample with an elongation value of 25.6% and a UTS value of 430 MPa was the ideal LOM sample. Conversely, the weakest sample was the LOM sample with a cross-profile, which had an elongation value of 10.8% and a UTS value of 332.5 MPa. This research could provide further information about the LOM method and the best straight-profile movement strategy. A suitable TIG gun movement strategy could produce a good LOM sample with a good microstructure, tensile strength, and ductility. Further research should incorporate more movement strategies and techniques that completely prevent the formation of pore defects.

Crystal Growth and Structural and Optical Characterizations of Mixed-Cation MA1-xCsxPbBr3 Halide Perovskite Solid Solutions

Photovoltaic devices fabricated using mixed-cation halide perovskites have demonstrated a superior combination of high efficiency and long operating life. In this study, we synthesize a series of mixed-cation halide perovskites with the composition of MA1-xCsxPbBr3 (MA= CH3NH3), where x varies from 0 to 1. We carefully examine various polar solvents and develop a relatively facile, room temperature solution-based growth method for growing these single crystals under optimal conditions. We conduct a comprehensive investigation of the influence of the Cs+ cation on the structure and optical properties of the perovskite solid solutions. The structural characterization using X-ray diffraction confirms the successful substitution of cesium for the methylammonium (MA) cation in the MA1-xCsxPbBr3 perovskite structure, with a continuous solubility. As the Cs+ content increases, the crystal structure undergoes a gradual transformation from a cubic phase (for MAPbBr3) to an orthorhombic phase (for CsPbBr3). To study the impact of Cs substitution on their optical properties, we perform UV-Vis absorption analysis, and find no significant change in the bandgap value, which remains approximately 2.12 - 2.14 eV for the compositions with x up to 0.7, and for x > 0.7, however, the bandgap value gradually increases to reach 2.21 eV for pure CsPbBr3. This work demonstrates a valid technique for the growth of halide perovskite solid solution crystals, which can be a versatile tool for tailoring the structure, long-term stability, and optoelectronic properties for advanced photovoltaic applications.

Multi-scale microstructure manipulation of an additively manufactured CoCrNi medium entropy alloy for superior mechanical properties and tunable mechanical anisotropy

Laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) technology has become a versatile tool for producing new microstructures in metal components, offering novel mechanical properties for different applications. In this work, enhanced ductility (∼55% elongation) and tunable mechanical anisotropy (ratio of ductility along vertical to horizontal orientation from ∼0.2 to ∼1) were achieved for a CoCrNi medium entropy alloy (MEA) by multi-scale synergistic microstructure manipulation (i.e., melt pool boundary, grain morphology and crystallographic texture) through adjusting key PBF-LB processing parameters (e.g., laser power and scan speed). By increasing the volumetric energy density (VED) from 68.3 to 144 J/mm3, the melt pool size enlarges, and the crystallographic texture transitions from <100>//BD to <110>//BD due to the maximum thermal flux direction changing for different melt pool dimensions, which affects the proportion of grains that have different growth directions. Moreover, excellent mechanical properties of 890 MPa ultimate tensile strength and ∼55% elongation to failure can be achieved for loading perpendicular to the build direction with only a ∼15% reduction in properties for loading along the build direction. The superior combination of mechanical properties is achieved by processing parameter-controlled strengthening of melt pool boundary interfaces, heterogeneous deformation induced strengthening through bimodal grain structures, and favorable grain orientation for dislocation slip and twinning formation, which was significantly more activated in the <110>//BD texture than in the <100>//BD. This study offers new insights into achieving multi-scale synergistic microstructure manipulation via PBF-LB for desired strength, ductility, and mechanical anisotropy in a CoCrNi MEA.

The effect of electrochemical treatment on the structure of single-walled carbon nanotubes: Towards better filling efficiency

Filled single-walled carbon nanotubes (f-SWCNT) are regarded as prospective materials with diverse applications, owing to the superior combination of their intrinsic properties with those of the filler material. The variety of the potential filler materials makes solution filling through open SWCNT channels under capillary forces the most flexible method for f-SWCNT production. However, the technique requires the additional step of SWCNT cap removal, and remains poorly efficient. Here, we evaluated how the structure of the SWCNTs impacts the filling efficiency depending on the conditions of electrochemical opening treatment under cyclic voltammetry protocols. We revealed the optimal upper vertex potential to be 1.1 V vs. RHE, corresponding to the trade-off between end-cap removal efficiency and yield of wall defect formation. It allowed us to achieve a filling efficiency of ∼1680 m cm−2 of gold nanowires length per unit SWCNT film area, which is ∼10 times greater than the filling efficiency of the untreated material.

In-situ synthesis of spatial heterostructure Ti composites by laser powder bed fusion to overcome the strength and plasticity trade-off

Recent research has focused on laser in-situ additive manufacturing of metal matrix composites with spatially controllable microstructures (phases). This study, inspired by the process of inserting mesh fibers into reinforced concrete, synthesizes TiN in situ using laser powder bed fusion and N2 gas. The laser-melted track, embedded with TiN particles, formed a spatially heterostructured Ti composite (SHTC) with a three-dimensional, artificially controlled architecture in a pure Ti matrix. The influences of process parameters on the mechanical properties of the spatially heterostructured Ti composite and the microstructural evolution of TiN/Ti were investigated emphatically. The results showed that the growth direction of the microstructure was changed by laser powder bed fusion additive manufacturing with alternating N2–Ar gas under suitable N2 concentration and melting track spacing. Among all spatially heterostructured Ti composites, the TiN–Ti heterolayer net-like structure achieved a high ultimate tensile strength of ∼1.0 GPa and elongation of 27 %, demonstrating a superior strength-ductility combination than intrinsic pure Ti and uniform TiN composites, as well as traditional layered structure Ti-based composites. During the tensile test, the deformation behavior was monitored in situ using digital image correlation, and the fracture mechanism was investigated. Hetero-deformation induced strengthening and toughening potentially explains the mechanism behind the strength enhancement of spatially heterostructured Ti composites. Furthermore, this work may stimulate research and development in additive manufacturing of spatial heterostructures with configurable structures, targeting synergistic regulation of strength and ductility in the integration of structure-material-function.

Achieving high performance by optimized heat treatment in a spray formed Al–Zn–Mg–Cu alloy

High strength Al–Zn–Mg–Cu alloys are widely used for structure components in engineering applications, such as aerospace, transportation, owing to a superior combination of high strength to density ratio and excellent mechanical properties. In present work, the effect of solution treatment and aging treatment on precipitates and mechanical property is investigated in a spray formed (SFed) Al–Zn–Mg–Cu alloy. The SFed Al alloy after optimized solution treatment shows fine grains and high fraction of substructures, which increase the kinetics for precipitation and refine precipitates. It is found that the aging temperature mainly affects the size and phase type of matrix precipitates, size of grain boundary precipitates and width of precipitate free zone. It confirms that both the strength and ductility are controlled by precipitates, which are strongly dependent on aging temperature. Specifically, the sample aged at 120 °C for 16 h (120 °C@16h) behaves highest yield strength (661 MPa) caused by the fine precipitates, while the sample aged with 100 °C@24h behaves highest ultimate tensile strength (745 MPa), uniform elongation (9.1 %) and total elongation (12.5 %). In addition, the strain hardening behavior of SFed Al–Zn–Mg–Cu alloy is discussed by Kocks-Mecking model and an empirical rule.

Heterogeneous plastic deformation and HDI strengthening of the heterostructured dual-phase steels investigated by in-situ SEM-DIC

Heterostructured dual-phase (DP) steels comprising different martensite volume fractions (HS740 steel, VM:41 %; HS780 steel, VM: 54 %) were produced by cold rolling and intercritical annealing. HS780 steel produces a near-ideal heterostructure where the grains are mostly isolated by the F/M interfaces, resulting in a superior combination of strength-ductility (ultimate tensile strength, UTS: 1064 MPa; uniform elongation, UE: 9.8 %). The excellent mechanical properties is primarily attributed to the stronger hetero-deformation induced (HDI) strengthening and hardening of HS780 steel. The relationships between HDI hardening and the heterogeneous plastic deformation of the heterostructured DP steels were elucidated based on the in-situ tensile tests and digital image correlation analysis. The insights from these results will improve our understanding of the deformation behavior of heterostructured materials and guide the design of low-carbon steels with outstanding mechanical properties.

Ultra-strong and ductile precipitation-strengthened high entropy alloy with 0.5 % Nb addition produced by laser additive manufacturing

Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys (HEAs) is challenging. The present work investigates the in-situ synthesis of Fe49.5Mn30Co10Cr10C0.5 interstitial solute-strengthened HEA containing 0.5 wt.% Nb (hereafter referred to as iHEA-Nb) using laser melting deposition (LMD), aiming at simultaneously activating multiple strengthening mechanisms. The effect of Nb addition on the microstructure evolution, mechanical properties, strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated. Multiple levels of heterogeneity were observed in the LMD-deposited microstructure, including different grain sizes, cellular subgrain structures, various carbide precipitates, as well as elemental segregation. The incorporation of Nb atoms with a large radius leads to lattice distortion, reduces the average grain size, and increases the types and fractions of carbides, aiding in promoting solid solution strengthening, grain boundary strengthening, and precipitation strengthening. Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa, respectively, while maintaining the elongation over 30 %. Deformation twins were generated in the tensile deformed samples, contributing to the occurrence of twinning-induced plasticity. This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date, demonstrating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments. In addition, single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA, the micromechanical properties of grains with different orientations were significantly enhanced.

Remarkable improved strength and ductility in brittle eutectic high-entropy alloy via a novel spheroidization and recrystallization strategy

Eutectic high-entropy alloys (EHEAs), as a classification of high-entropy alloys (HEAs), have received worldwide interest due to superior fluidity and attractive properties. However, other than the FCC + B2 EHEA system, most other reported EHEA systems show inherent brittleness during tensile loading at room temperature, which limits their advanced engineering application. In this work, a novel spheroidization + recrystallization (SR) strategy for synergistic strengthening and plasticizing of the brittle CoCrFeNi2(V6B3Si)0.149 was proposed. The superior combination of strength and ductility was achieved by tailoring spherical M3B2 + recrystallized FCC duplex phases. Based on this strategy, the yield strength and elongation were improved from 565 ± 15 MPa and 2.3 % ± 0.3 % to 841 ± 24 – 1278 ± 20 MPa and 14.7 % ± 0.5 % – 22.5 % ± 1.2 %, with an increase of 48 %–126 % and 539 %–878 %, respectively. The synergistic increment in the strength and ductility of SR-FCC+M3B2 EHEAs exceeds all reported further strengthened FCC + B2 EHEAs. Meanwhile, such simple thermo-mechanical processing is suitable for large-scale industrial production. The high strength results from the back stress provided by the dual heterogeneity of FCC grain sizes and soft FCC/hard M3B2. The good ductility is attributed to the dislocation movement path released by spheroidized M3B2 and a more uniform stress distribution caused by the recrystallized FCC. This work provides a new strategy for synergistic strengthening and plasticizing of the brittle EHEAs to meet industrial reliability requirements.

Three-dimensional numerical simulation and structural optimization of large steam ejectors in exhaust gas heat recovery systems

By establishing a three-dimensional mathematical model based on the physical characteristics of the steam ejector and utilizing computational fluid dynamics (CFD) method, this study conducted three-dimensional numerical simulations to investigate the effects of five key structural parameters, namely, the length of the nozzle diffuser section, the diameter of the nozzle outlet, the length of the contraction section in the mixing chamber, the diameter of the mixing chamber inlet, and the length of the mixing chamber throat, on the ejector performance under identical operating conditions. By fitting 50 sets of simulation data using the least squares method, analytical expressions for these structural parameters in terms of the ejection coefficient μ were obtained. Subsequently, an improved firefly algorithm was employed to identify the optimal combination of structural parameters, followed by simulation verification. The results showed that compared to the single-factor sensitivity analysis method, the improved firefly algorithm obtained a superior combination of structural parameters, resulting in a 2.03% enhancement in the ejection performance of the steam ejector.

Composition design study of strong and ductile Mo-alloyed CoCrNi medium-entropy alloys

The assistance of alloying elements provides enormous opportunities for the discovery of high-performance face-centered cubic (FCC) medium-entropy alloys (MEAs). In this work, the influence of alloying element Mo on the phase stability, stacking fault energy (SFE), deformation mechanisms, lattice distortion, and mechanical properties of (CoCrNi)100–xMox (0 ≤ x ≤ 10) MEAs was synthetically explored with the first-principles calculations. It indicates that the FCC phase remains metastable at 0 K, and its stability degenerates with increasing Mo content. The monotonous decrease of SFE is revealed with the rise of Mo content, which promotes the activation of stacking faults, deformation twinning, or martensitic transformation. Raising Mo content also causes the aggravation of lattice distortion and thus triggers intense solid solution strengthening. Significantly, the essential criterion for the composition design of FCC (CoCrNi)100–xMo MEAs with superior strength-ductility combination was established based on the synergistic effects between multiple deformation mechanisms and solid solution strengthening. According to the criterion, the optimal composition is predetermined as (CoCrNi)93Mo7 MEA. The criterion is proved to be effective, and it can provide valuable inspiration for the development of alloying-element reinforced FCC multi-principal element alloys.

Towards high strength and ductility of Al–Cu-Mg alloy via cyclic and monotonic pre-straining followed by ageing

This article presents an investigation of the ageing response of modern high-strength aluminium alloy 2519 (Al–5.64Cu-0.33Mn-0.23Mg-0.01Si (wt%)) after cyclic strengthening (CS). The impact of the pre-straining value on the mechanical properties, microstructure and phase composition was elucidated via hardness and tensile testing, analytical transmission and orientation imaging electron microscopy. The results show that cyclic hardening has a significant impact on the ageing behaviour of the alloy. Applying cyclic pre-straining in conjunction with monotonic enhances strength and ductility at once. This novel high-performance treatment results in superior strength-ductility combination. The improved mechanical properties are attributed to the observed changes in microstructure. The introduction of vacancies and dislocations, by repetitive and elastic straining before artificial ageing, leads to great homogeneous structure and an increase in the number density and volume fraction of the main strengthening phases (θ′ and Ω) and clusters/zones. Therefore, this work should suggest a strategy for developing a novel treatment of aluminium alloys with excellent mechanical properties.

Controllable precipitation behavior near grain boundaries enabled by artificial strain concentration in age-hardening aluminum alloys

Regulating the precipitation behavior in the vicinity of grain boundary (GB) is crucial for improving the mechanical property and corrosion resistance of age-hardening aluminum alloy. In this work, we innovatively propose a strain-concentration controlled strategy to realize the controllable fabrication of the thinner precipitate-free zone (PFZ), associated with the finer grain boundary precipitates in Al–Zn–Mg–Cu alloy. Specifically, the primary PFZ with certain solute atoms is introduced by short pre-aging treatment, followed by the subsequent cyclic deformation at room temperature to induce the localized plastic deformation in the primary PFZ. Compared with the traditional aging, the Al–Zn–Mg–Cu alloy treated by the current process manifests superior combination of impact toughness and corrosion properties, as well as the slightly improved unidirectional tensile properties. Furthermore, the atomic-scale mechanism of the unique precipitation behavior near GB is revealed using the molecular dynamics simulation. A large number of dislocations are generated in PFZ, which acts as the favorable precipitation sites and contribute to the secondary precipitates in the primary PFZ. The present work provides a novel design route and an atomic-scale understanding for controlling the precipitation behavior in the vicinity of GB, and it has the potential to direct the optimization of mechanical performance and corrosion resistance in a board spectrum of aging-hardening alloys.