Trade-off Dilemma Research Articles

Evading strength−ductility trade-off of GH605 alloy using magnetic field-assisted undercooling treatment

Undercooling solidification under a magnetic field (UMF) is an effective way to tailor the microstructure and properties of Co-based alloys. In this study, by attributing to the UMF treatment, the strength−ductility trade-off dilemma in GH605 superalloy is successfully overcome. The UMF treatment can effectively refine the grains and increase the solid solubility, leading to the high yield strength. The main deformation mechanism in the as-forged alloy is dislocation slipping. By contrast, multiple deformation mechanisms, including stacking faults, twining, dislocation slipping, and their strong interactions are activated in the UMF-treated sample during compression deformation, which enhances the strength and ductility simultaneously. In addition, the precipitation of hard Laves phases along the grain boundaries can be obtained after UMF treatment, hindering crack propagation during compression deformation.

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.

Diversity and Serendipity Preference-Aware Recommender System

Diversity and novelty are essential objectives in recommender systems to improve stakeholders' benefits by reducing user's discovery efforts and improving business operators' sales and revenue. Existing diversity and novelty-based methods indifferently increase diversity or novelty for every user, which inevitably induces the trade-off dilemma between relevance and accuracy. Moreover, different users have different preferences for recommendation diversity and novelty. Such preference should be considered by a recommendation algorithm, thereby avoiding the trade-off dilemma and increasing the prediction accuracy. To address this research gap, we propose a new Diversity and Serendipity-Aware Recommender System (DSPA-RS) problem and its solution method. The MovieLens-2k data are used to evaluate our proposed DSPA-RS method against seven widely used recommendation methods in recommender systems as benchmarks. The test results demonstrate our method shows a superior performance than the benchmarks by a range of 34.30% to 108.27%, indicating that the movies recommended by our method best satisfy users' diversity and serendipity preference. For recommendation accuracy, our DSPA-RS method outperforms the most accurate method by 34.62% in Precision, 7.71% in Recall, and 24.37% in F1 score. The improvement in recommendation accuracy indicates that DSPA-RS's consideration and utilization of diversity preference and novelty momentum greatly improves recommendation quality. Received: 28 April 2024 | Revised: 12 June 2024 | Accepted: 8 July 2024 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement The MovieLens10M data set that support the findings of this study are openly available at https://doi.org/10.1145/2827872, reference number [48]. The MovieLens-2k data set that support the findings of this study are openly available in Grouplens at https://grouplens.org/datasets/hetrec-2011/. Author Contribution Statement Kexin Yin: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data Curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition. Junqi Zhao: Writing – original draft, Writing – review & editing, Visualization, Project administration.

Evading the strength and toughness trade-off dilemma in Lu2Si2O7 environmental barrier coatings via micro-nano reinforcement

Lu2Si2O7 nanostructured environmental barrier coating was prepared using as–synthetic Lu2Si2O7 feedstock via atmospheric plasma spraying. The structure and mechanical performances of Lu2Si2O7 coatings were characterized in detail. Results indicate that nanostructured Lu2Si2O7 coating exhibits a bi-modal microstructure, lamella structure and unmelted particles. The phase components of nanostructured Lu2Si2O7 coatings consist of β-Lu2Si2O7 and a small number of X2-Lu2SiO5. Furthermore, the nanohardness and elastic modulus of Lu2Si2O7 coatings have the characterization of bi-modal properties via Weibull analysis, i.e., the large Weibull modulus and the small Weibull modulus represent molten lamella structure and unmelted particles, respectively. Meanwhile, the fracture toughness of nanostructured Lu2Si2O7 coatings is superior to conventional Lu2Si2O7 coatings, and the adhesion strength of Lu2Si2O7 coatings is about 22.6 MPa by pull-extend test. Results of research are helpful for the design and preparation of advanced thermal spray coating.

Enhanced strength–ductility synergy in Ti55531 titanium alloys through gradient microstructural design strategy

The strength-ductility trade-off dilemma still exists for titanium alloys, which is a challenging and pressing issue within the realm of microstructure design and property control. In the present work, a typical axial gradient microstructure was prepared in Ti55531 titanium alloy through a composite strengthening process involving rapid electropulsing treatment (EPT) combined with step-quench treatment (SQT). The results show that a significant improvement of 450 MPa (54 %) and 6.3 % (100 %) for the strength and ductility are obtained respectively for gradient microstructure by EPT + SQT (GMES) compared to that gradient microstructure prepared by EPT (GME) only. This indicates that the enhanced strength-ductility synergy observed in GMES is attributed to the characteristic Twinning induced Plasticity (TWIP) mechanism employed in this novel design of gradient microstructure. Furthermore, a detailed analysis and discussion are provided on the physical deformation mechanism and crack initiation behaviour of the gradient microstructure, providing valuable insights for the design of high-strength, high-ductility metals such as beta titanium alloys, advanced steels, and multi-phase alloys.

Overcoming the strength-ductility trade-off dilemma in austenitic lightweight steel via stepwise controllable intragranular dual nanoprecipitation

The strength-ductility trade-off is an inevitable scenario in precipitation-hardened austenitic lightweight steels. The reduction in ductility is due to the shearing of κ′-carbides by dislocations, resulting in limited work hardening capability. Conversely, non-shearable B2 particles can effectively improve the work hardening rate. However, these B2 particles tend to precipitate along grain boundaries and coarsen due to their incompatibility with the austenite matrix, resulting in negligible strengthening effect or even brittleness. We propose a stepwise controllable dual nanoprecipitation strategy to overcome the strength-ductility trade-off. To implement this strategy, we develop a manufacturing process that includes a high-temperature annealing treatment and a three-step aging process (700 °C/15min + 900 °C/15min + 450 °C/1 h). The higher annealing temperature increases the supersaturation of solute atoms in the austenite matrix, which improves the chemical driving force for the precipitation of intragranular B2 particles during aging at 900 °C. Additionally, the coarsened κ′-carbides (30–35 nm) formed during aging at 700 °C provide heterogeneous nucleation sites for the formation of intragranular B2 particles. Further aging at 450 °C promotes the precipitation of nano-sized κ′-carbides (5 nm) within the austenite matrix. The dual nanoparticles provide a significant precipitation strengthening contribution of 400 MPa without sacrificing ductility. The multiple deformation mechanisms of nanoscale “planar slip and Orowan bowing” provide an efficient source of work hardening capability. The present work aims to overcome the strength-ductility trade-off in austenitic lightweight steels by tailoring the precipitation process, which may provide insight into producing high-performance lightweight steels.

Investigation of a novel laser powder bed fusion nickel-based superalloy with hf, Y addition: Melt characteristic, microstructure and mechanical properties

In order to resolve the inherent strength-ductility trade-off dilemma observed in precipitation-strengthened nickel-based superalloys with high Al and Ti content, a composition modification strategy was devised. This study explored a novel laser powder bed fusion (LPBF) René104 alloy by incorporating Hf and Y (HfY-René104), examining its melt characteristics, microstructures, and mechanical properties. The experimental results demonstrate that the addition of Hf and Y effectively improves the molten pool structure of the as-built, alters grain orientation, diminishes grain aspect ratio, promotes the formation of cellular structures, AlY phases, stacking faults (SFs), and Lomer-Cottrell (L-C) locks at macro, meso, and micro scales, respectively. The primary contributors to yield strength are grain boundary strengthening and dislocation strengthening. Moreover, a dynamic Hall-Petch effect associated with cellular structures, SFs, and L-C locks ultimately results in remarkable strength (yield strength of 823 MPa, ultimate tensile strength of 1158 MPa) and enhanced ductility (elongation of 24.6 %) of HfY-René104 alloy.

Designing the heterogeneous microstructure via a direct warm rolling process to synergistically enhance the strength-ductility in a medium Mn steel

This work introduced a facile method for fabricating heterostructures in a medium Mn steel via a direct warm rolling process. The heavy warm rolling promoted the transformation of metastable austenite (∼12.2 vol%) into hard domain α’ martensite, which formed a heterogeneous microstructure with the untransformed γ (soft domain). After 600 °C re-annealing, the hard domain α’ re-reversed to α + γ, and the heterostructure disappeared. Compared to the homogeneous structure, the heterostructure exhibited the synergistic enhancement of strength-ductility (yield strength (YS): 782 → 1113 MPa; ultimate tensile strength (UTS): 1099 → 1304 MPa; total elongation (TEL): 20.8 % → 21.7 %). Quantitative analysis showed that the heterogeneous deformation induced (HDI) strengthening (∼261 MPa) was the primary contributor to the increased ΔYS (782 → 1113 MPa) value, rather than the traditional strengthening mechanisms. Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effect were the main deformation mechanisms of both homogeneous/heterogeneous structures. However, compared to the homogeneous microstructure, the heterogeneous structure possessed the more pronounced TRIP and HDI hardening effects as well as L-C locks, the cooperative effect of these three factors further improved the strain hardening ability to break through the strength-ductility trade-off dilemma.

Enhancing strength and ductility of extruded Ti-alloy-reinforced Al-Mg-Si composites: Roles of interface nanostructures and chemical bonding

A comprehensive understanding of interface nanostructures and chemical interactions is required for solving the strength-plasticity trade-off dilemma of Al/Ti composites. Continuously Ti-reinforced Al-matrix composites with superior strength and ductility are fabricated via a novel extrusion technique. The unique strain-hardening mechanism of the Al/Ti composite plates at low strains is attributed to the coupling effects of the strong interface constraint potency, the mechanical incompatibility between the soft Al and hard α-Ti, and a large elastic strain of hard α-Ti. Interlocking structures with atomic interdiffusion are observed at the Al/Ti interface. Mechanical and thermal effects induce lattice distortion and atomic superdiffusion, thus resulting in an interfacial intermixing zone with substantial dislocations and misfit strain. These characteristics produce a strong interface constraint effect during tensile, causing superior strain/dislocation hardening and uniform plasticity. Nanoclusters with cubic structures and dispersed dislocations are detected in the three-dimensional (3D) atomic intermixing zone at the Al/TiAl3 interface, accompanied by the aggregation of Mg. The nanostructures with numerous dislocations in the 3D Ti/TiAl3 transition zone feature lattices with partially tetragonal structures and ordered Ti-Al(Si) clusters. Ab initio calculations indicate that the strong chemical interaction between Si and Ti atoms not only improves the interface bonding strength, but also disturbs the lattices and broadens the transition zone. Moreover, the 3D interface transition zones, accompanied by dispersed dislocations, improve the interface constraint potency and hardening capability of the annealed Al/Ti composite plate. This work sheds light on the capability of the extrusion technique to produce fiber-reinforced Al-matrix composites with superior mechanical properties and provides new strategies for improving the chemical bonding strength and interface constraint effect via the interface invasion of specific elements.

Achieving the strength-ductility synergy in ultra-fined grained CNT/2024Al composites via a low-temperature aging strategy

Synchronous enhancement of strength and ductility is a persistent challenge in the development and application of carbon nanotube (CNT)-reinforced aluminum matrix composites. This study proposed a low-temperature aging strategy to induce the nanoscale precipitates and evade the strength and ductility trade-off dilemma. The composites under various aging conditions were characterized in detail at the macro, micro, and nano scales. The precipitation behavior and strengthening mechanism were investigated systematically. Results indicated that the composite exhibited a better mechanical performance when aged at 100 °C. Compared to as-extruded composites, the yield and ultimate tensile strength of CNT/2024Al composites increased by 82.7 % and 64.8 %, respectively, whereas the elongation decreased by only 1.1 %. The results of microstructure and theoretical estimation suggested the dense nanoscale GP zones were primarily responsible for achieving the strength-ductility synergy. This present study on tailoring precipitate evolution could provide fundamental insights and references to enhance the mechanical properties of aluminum matrix composites.

Learning Commonsense-aware Moment-Text Alignment for Fast Video Temporal Grounding

Grounding temporal video segments described in natural language queries effectively and efficiently is a crucial capability needed in vision-and-language fields. In this paper, we deal with the fast video temporal grounding (FVTG) task, aiming at localizing the target segment with high speed and favorable accuracy. Most existing approaches adopt elaborately designed cross-modal interaction modules to improve the grounding performance, which suffer from the test-time bottleneck. Although several common space-based methods enjoy the high-speed merit during inference, they can hardly capture the comprehensive and explicit relations between visual and textual modalities. In this paper, to tackle the dilemma of speed-accuracy tradeoff, we propose a commonsense-aware cross-modal alignment network (C 2 AN), which incorporates commonsense-guided visual and text representations into a complementary common space for fast video temporal grounding. Specifically, the commonsense concepts are explored and exploited by extracting the structural semantic information from a language corpus. Then, a commonsense-aware interaction module is designed to obtain bridged visual and text features by utilizing the learned commonsense concepts. Finally, to maintain the original semantic information of textual queries, a cross-modal complementary common space is optimized to obtain matching scores for performing FVTG. Extensive results on two challenging benchmarks show that our C 2 AN method performs favorably against state-of-the-arts while running at high speed. Our code is available at https://github.com/ZiyueWu59/CCA.

Superior mechanical properties of additively manufactured FV520B matrix composites by microstructure tailoring

The additively manufactured martensitic stainless steel (SS) parts often manifest the strength-ductility trade-off dilemma, which severely limits their practicality. In this study, the TiC-reinforced FV520B metal matrix composites (MMCs) were deposited via laser powder bed fusion (LPBF), and the as-built MMCs exhibited a superior strength-ductility synergy (ultimate tensile strength of 1,389±29 MPa, and fracture elongation of 30.1±0.6 %) when compared to their matrix alloy. This strength-ductility synergy can be attributed to a high-density of well-dispersed TiC nanoparticles, in-situ grain boundary engineering induced by TiC particles, fully austenite structure, and progressive transformation-induced plasticity effect. Furthermore, the microstructure, and mechanical properties of the MMCs annealed at 400–700 °C were compared. As the annealing temperature increases, the matrix progressively transforms from a fully austenite structure to a fully martensite structure, enabling substantial enhancements in tensile strength and work hardening capabilities. Notably, a high number density of the Cu-rich precipitates (CRPs) can be observed in the high-temperature annealed specimen, which can yield considerable strengthening through the Orowan looping mechanism. This work paves a pathway to fabricate structural materials with unique microstructures and excellent mechanical properties for practical engineering applications.

Strengthening complex concentrated alloy without ductility loss by 3D printed high-density coherent nanoparticles

Metallic 3D printing enables fast fabrication of net-shaped components for broad engineering applications, yet it restrains the use of most mechanical processing methods for strengthening alloys, e.g. forging, rolling, etc. Here, we proposed a new strategy for enhancing the strength of 3D printed complex concentrated alloys without losing ductility. This strategy relies on the rapid cooling of 3D printing to achieve a supersaturation state that is beyond conventional casting. Then, spinodal decomposition via aging is exploited to introduce high-density coherent nanoparticles for strengthening. The proposed strategy is demonstrated in a 3D printed Cu-based complex concentrated alloy. The rapid solidification during printing strongly inhibits elemental diffusion, leading to a high supersaturation state. High-density nanoparticles with coherent interface and size of ∼7 nm are introduced into the 3D printed samples through spinodal decomposition via simple aging treatment. The strength of the 3D printed alloy is increased by 30 % after aging with no ductility loss, leading to a strength-ductility combination superior to other Cu alloys. This strategy is readily applicable to other spinodal alloys fabricated by 3D printing for circumventing the strength-ductility trade-off dilemma.

Achieving high strength-ductility synergy in TiBw/near α-Ti composites by ultrafine grains and nanosilicides via low-temperature severe plastic deformation

The common problem of low strength-ductility matching prevails in near-α high-temperature titanium matrix composites (TMCs). In this work, the design strategy of ultrafine grains and dispersed (Ti, Zr)6Si3 nanoprecipitates in the microstructure of TiBw/near α-Ti composites via low-temperature isothermal multidirectional forging (IMDF), is expected to break the trade-off dilemma between strength and ductility. The results show that with the decrease in the temperature of IMDF, the grain scale decreased from 0.98 to 0.59 μm, and the location of silicide precipitation shifted from phase boundaries and grain boundaries to α-grain boundaries and intracrystalline regions. The experiments confirm that the local segregation of Si and the temperature of thermomechanical deformation are the key factors affecting the precipitation behavior of silicides. With the decrease of the deformation temperature, the precipitation mechanism of silicides changes from a single diffusion-controlled precipitation to the coupling of two mechanisms, namely, elemental diffusion and dislocation-assisted nucleation, which facilitates the successive precipitation of nanometer-sized silicides at the grain boundaries and in the inner regions. The ultimate tensile strength (UTS) and elongation of the composites were substantially increased after IMDF at 950 and 800 °C, especially the excellent performance at 800 °C, where the strength reached 1320.3 MPa and the elongation was 5.8 %. The room and high-temperature strengthening and failure mechanisms of the composites are analyzed and discussed, and the yield strength (YS) increments provided by various strengthening mechanisms at room temperature are quantified, aiming to provide a potential preparation strategy for the synergistic strengthening of near-α TMCs with ultrafine grains and nanoparticles.

Large deformation response of a novel triply periodic minimal surface skeletal-based lattice metamaterial with high stiffness and energy absorption

Triply periodic minimal surface (TPMS) lattice metamaterials present superior mechanical performance over traditional strut-based lattice metamaterials due to their unique structural characteristics. However, the high stiffness–stable plastic response trade-off dilemma is still the major challenge for skeletal-based metamaterials. Herein, a novel TPMS skeletal lattice metamaterial is proposed. Finite element simulations are conducted to reveal its elastic properties and plastic response under compression. Afterwards, validation experiments are performed on the lattice specimens fabricated by the most common Fused Deposition Modeling (FDM) process. The nominal stress–strain curves and collapse mode of the lattice materials are obtained accordingly. Both the numerical simulations and experiments demonstrate that the proposed TPMS lattice metamaterial exhibits high specific modulus, strength and energy absorption, together with a smooth and elongated stress plateau, thereby overcoming the strength-efficiency trade-off. Different from the rigid nodal region in traditional strut-based lattices, the strut connection parts in the novel TPMS lattices experience shear and twisting, which avoids the catastrophic failure of the struts and enhances the loading efficiency of the structure under compression. Meanwhile, the numerical results indicate that the stable plastic response of the designed architecture is insensitive to the plastic flow behavior of the bulk material, which is also supported by the experimental results. It is also demonstrated that the novel TPMS lattice metamaterial presents several times higher stiffness as well as energy absorption simultaneously than the current strut-based lattice materials, which can be potentially applied as load-bearing components and impact energy absorbers.

Excellent strength-ductility synergy properties of Mg–Sn–Zn–Zr alloy mediated by a novel differential thermal ECAP (DT-ECAP)

The application of structural magnesium (Mg) alloys in engineering industry is usually impeded by the challenge of strength-ductility synergy. In this study, a considerable ductility (elongation, ∼27–33 %) and high ultimate tensile strength (UTS, ∼340–370 MPa) Mg–Sn–Zn–Zr alloy was developed by a combination of aging, extrusion and novel differential thermal equal-channel angular pressing (DT-ECAP) process. Both dislocation slip and (double) cross-slip are primary deformation mechanisms of the alloy. Furthermore, jogs or kinks induced by the interaction between high density of dislocations were also observed in the alloy before and after tensile test, indicating good deformability. More importantly, based on the two-beam bright-filed TEM under three g conditions, multiple slip systems containing pyramidal <c + a>, prismatic and basal <a> dislocations were activated to accommodate both c-axis and a-axis strains of the alloy, leading to superior work-hardening effect and thus superb ductility. On the other hand, the DT-ECAP process was in favor of grain refinement and ultrafine second phases with ∼54–63 nm. Therefore, the principal strengthening mechanisms of the DT-ECAPed alloys were grain boundary strengthening, precipitation strengthening and dislocation strengthening. The contributions of the three strengthening mechanisms to TYSs of second pass (2P) and forth pass (4P) alloys are ∼77 MPa and ∼66 MPa, ∼30 MPa and ∼27 MPa, ∼34 MPa and ∼27 MPa, respectively. The current work develops a novel DT-ECAP process for preparing a new Mg–Sn–Zn–Zr alloy with strength-ductility synergy and provides a strategy to break the strength-ductility tradeoff dilemma of rare-earth-free Mg alloy.

Biphase Pd Nanosheets with Atomic-Hybrid RhOx/Pd Amorphous Skins Disentangle the Activity-Stability Trade-Off in Oxygen Reduction Reaction.

The activity-stability trade-off relationship of oxygen reduction reaction (ORR) is a tricky issue that strikes the electrocatalyst population and hinders the widespread application of fuel cells. Here neoteric biphase Pd nanosheets that are structured with ultrathin two-dimensional crystalline Pd inner cores and ≈1 nm thin atomic-hybrid RhOx/Pd amorphous skins, named c/a-Pd@PdRh NSs, for disentangling this trade-off dilemma for alkaline ORR are developed. The superthin amorphous skins significantly amplify the quantity of flexibly low-coordinated atoms for electrocatalysis. An in situ selected oxidation of the top-surface Rh dopants creates atomically hybrid RhOx/Pd disorder surfaces. Detailed energy spectra and theoretical simulation confirm that these RhOx/Pd interfaces can arouse a surface charge redistribution, causing significant electron deficiency and lowered d-band center for surface Pd. Meanwhile, anticorrosive Rh/RhOx species can thermodynamically passivate the neighboring Pd atoms from oxidative dissolution. Thanks to these amplified interfacial effects, the biphase c/a-Pd@PdRh NSs simultaneously exhibit a superhigh ORR activity (5.92 A mg-1, 22.8 times that of Pt/C) and an outstanding long-lasting stability after 100k cycles of accelerated durability test, showcasing unprecedented electrocatalysts for breaking the activity-stability trade-off relationship of ORR. This work paves a bran-new strategy for designing high-performance electrocatalysts through creating modulated amorphous skins on low-dimensional nanomaterials.

A deep-learning-based compact method for accelerating the electrowetting lattice Boltzmann simulations

Research on the electrowetting of micro- and nanoscale droplets is essential for microfluidics and nanomaterials applications. A lattice-Boltzmann-electrostatics (LBES) method is an effective and accurate method for simulating this process. However, the electric potential field in each time step requires numerous iterative calculations to converge. Therefore, there is a trade-off dilemma between using high-density lattice fields to improve simulation refinement and low-density lattice fields to reduce computing costs in simulations. Fortunately, deep learning techniques can enhance the computing efficiency of electric potential fields, providing an efficient and accurate solution for electrowetting studies in fine-grained fields. In this study, a compact LBES (C-LBES), a computationally accelerated model for an electric potential field with spatiotemporal prediction capability, is developed by combining the advantages of a recurrent residual convolutional unit and a convolutional long-short-term memory unit. A loss function incorporating a geometric boundary constraint term and a self-cyclic prediction scheme are introduced according to the characteristics of the prediction task, which further improves the prediction accuracy of the model and the computing efficiency of the electric potential field. The model is validated with small datasets, and the results show that the C-LBES model with the self-cyclic prediction scheme improves the computing efficiency of the conventional LBES method by a factor of 10 and provides high-precision results when predicting a two-dimensional convergent electric potential field with a lattice size of (110, 160). In the generalization experiments, the average absolute error of the calculated results remains in the same order of magnitude as the accuracy experimental results.

Microstructure and enhanced strength and ductility of Ti-Zr-O alloys prepared by a laser powder bed fusion process

Non-toxic and biocompatible Ti-Zr-O alloys with excellent comprehensive properties of strength and ductility were prepared from Ti-ZrO2 powder mixtures by a laser powder bed fusion (LPBF) process. The substitutional Zr atoms and interstitial O atoms, formed by decomposition of ZrO2 during laser irradiation, were dissolved into crystal lattice of Ti, resulting in significant increases in lattice constant c and axial ratio c/a. The Ti-Zr-O alloys were characterized by fine needle-like microstructure with weakened texture compared to pure Ti. The needle-like microstructure may be generated through the growth of α-nuclei according to the Burgers orientation relationship during β→α phase transformation, and the reduction of crystallographic anisotropy in the Ti-Zr-O alloys is due to the formation of α grains with multiple variants. The LPBFed Ti-Zr-O alloys exhibited significantly enhanced strength and maintained good ductility, overcoming the strength-ductility trade-off dilemma. For example, the yield strength and ultimate tensile strength (UTS) of the Ti-1.48Zr-0.66 O alloy reached 1014 MPa and 1073 MPa, respectively, and its elongation at fracture remained at 17 %. The strength enhancement is due to the solid solution strengthening of O and Zr and grain refinement strengthening, of which the solid solution strengthening of interstitial O atoms is the most dominant contributor to the improvement in strength of the LPBFed Ti-Zr-O alloys. The good ductility is mainly attributed to the activation of pyramidal slips due to reduced critical resolved shear stress (CRSS) ratios between pyramidal and prismatic planes, especially dislocation slips along <c + a> directions on the pyramidal planes due to the fine-grained microstructure. The activation of multiple slip systems, including prismatic and pyramidal slips, contributes to the improved ductility of the LPBFed Ti-Zr-O alloys.

Exceptional ductility through interface-constrained grain growth for the ultrafine-scale Ni/Ni-W layered composites

Enhancing the strength of metallic laminates through decreasing the constituent layer thickness from micrometer to nanometer scale is usually accompanied by the degradation of ductility because plastic instability characterized by fatal shear bands inevitably occurs in the early stage of deformation. To overcome the strength-ductility trade-off dilemma, we designed a kind of metallic layered composites (LCs) consisting of nano-grained Ni (grain size: 21–37 nm) and ultrafine nano-grained Ni-W (grain size: 8 nm) constituent layers with layer thickness ranging from microns to tens of nanometers. We found that the strength and ductility of Ni/Ni-W LCs can be simultaneously enhanced by decreasing the layer thickness. Interface-constrained grain growth in the Ni layers with an initial layer thickness of less than 1 μm enhances strain hardening ability. Thus, strain delocalization characterized by the formation of rectangular strain zones instead of crossed micro shear bands appears in the LCs. Based on the above mechanism, we obtained the optimum ratio of the layer thickness to the grain size for the nano-grained Ni layers as about 15:1, which corresponds to Ni0.25/Ni-W0.025 LCs with the highest tensile strength (1.9 GPa) and elongation to failure (5.5 %). These findings may provide a new path for the design principle of metallic LCs with multi-level microstructural and geometrical scales.