Journal of Materials Science & Technology最新文献

Ni/TiAl composite brazed joints could significantly reduce the aircraft's weight. However, low interfacial adhesion, coarse and brittle-hard intermetallic compounds (IMCs) seriously limited the application of Ni/TiAl composite joints in the next generation of aerospace applications. So enhanced K4169/TiAl composite joints were investigated by vacuum brazed with (Ni_53.33Cr₂₀B_16.67Si₁₀/Zr₂₅Ti_18.75Ta_12.5Ni₂₅Cu_18.75) composite filler metal (CFM) designed based on cluster-plus-glue-atom model. The shear strength of the joint reached 485 MPa, comparable to the 491 MPa of TiAl substrate. The flat and brittle-hard diffusion reaction layer between Zones I and II was eliminated, simultaneously generating CrB₄ dispersion strengthening due to the CFM developed with the interfacial solid-liquid space-time hysteresis effect. In Zones II and III, IMCs all transformed into Ni_ss(Cr,Fe)_[0-88], Ni_ss(Ti, Al)_[004], and Ni_ss(Zr,Si)_[11-2] of circular and oval shapes through isothermal solidification. Meanwhile, the residual stresses and hardness were distributed in reticulated cladding characteristics. Thereby, lattice distortion led to solid solution strengthening and increased plastic toughness through crack termination and bridging mechanisms, which inhibited dislocations from plugging and crack propagation. Various interfaces in Zone Ⅳ were regulated into semi- and coherent interfaces. Ni₃(Ti,Al)/(Ni,Ti,Al) and (Ni,Ti,Al)/AlNi₂Ti were composed of higher interfacial bonding energy (2.771 J/m², 2.547 J/m²) and Ni-Ni covalent bonds. Interfacial covalent bonding and large interfacial bonding energy coupling strengthened Zone IV. Consequently, cracks initiated at the (Ni,Ti,Al)_[013]/Ti₃Al_[010] and expanded rapidly into TiAl substrate. Therefore, applying this method to design CFMs and regulate the phase, grain morphology, and interface's fine structure could provide new pathways for dissimilar hard-to-join metals.

The strength of non-heat-treatable 5xxx Al alloys is derived from solid solution strengthening and strain hardening, the absence of a precipitation strengthening response results in their lower strength. In this study, significant improvements in strength can be achieved by subjecting three different Mg concentrations 5xxx Al alloys to cyclic plasticity. A quantitative analysis of the respective contributions to the yield strength has been conducted by combining transmission electron microscopy and atom probe tomography. Additionally, the fatigue performance and fatigue mechanism of the cyclic strengthened 5xxx Al alloys have been thoroughly studied due to its transformation from non-heat-treatable to precipitation strengthening. We demonstrate that the high-cycle fatigue (HCF) strength of the cyclically strengthened state only experiences a minor improvement compared to the as-received state, which is significantly disproportionate to the enhancement in tensile strength. This disparity is primarily attributed to the changes in microstructure and fatigue mechanisms, resulting in a reduction in fatigue ratio. This study provides important insights for expanding research on cyclic plasticity methods in fatigue performance, and can aid in the development of improved processes for optimal fatigue resistance.

Succinonitrile has shown significant promise for application in polymer electrolytes for solid-state lithium metal batteries due to its high ionic conductivity at low-temperature. However, the use of Succinonitrile is limited due to its corrosion of Li metal. Herein, we report a solid polymer electrolyte with high ionic conductivity (2.17 × 10⁻³ S cm⁻¹, 35 °C) enhanced by Ti₃C₂T_x. Corrosion of the Li anode is prevented due to the Succinonitrile molecules being efficiently anchored by Ti₃C₂T_x. Meanwhile, the coordination environment of Li⁺ is weakened due to the introduction of competitive coordination induction effects into the polymer electrolyte, resulting in efficient Li⁺ conduction. Furthermore, the mechanical properties of the electrolyte are enhanced by modulating the ratio of Ti₃C₂T_x to suppress the growth of Li dendrites. Therefore, Li||Li symmetric batteries deliver stable cycling up to 8000 h at 28 °C. LiFePO₄||Li full batteries exhibit excellent cycling stability of 151.7 mAh g⁻¹ with a capacity retention of 99.3% after 300 cycles. This work not only presents a new idea to suppress the corrosion of the Li anode by Succinonitrile but also provides a simple, feasible, and scalable strategy for high-performance Li metal batteries.

Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondary α-phase (α_s) from β-matrix but often compromise ductility due to the conventional strength-ductility trade-off. In this study, a new strategy based on β-subgrains-mediated hierarchical α-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe (wt.%) alloy through a unique combination of hot rolling, short-term solid solution, and aging treatment, i.e., RSST+A. Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of ∼1581 MPa and decent ductility of ∼8.4%, surpassing ∼1060 MPa and ∼2.7% of the corresponding RSST counterparts without final aging treatment. This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting of β-subgrains-mediated hierarchical α-precipitates as a result of our specific processing approach. The designed short-term solution introduces abundant β subgrains that are transformed from the retained intensive dislocations during hot rolling. The β subgrain boundaries subsequently promote a dramatic precipitation of α allotriomorphs (α_GB) and Widmanstätten side-plates (α_WGB), which effectively subdivides β grains into numerous tiny independent deformation units. Consequently, plastic strain is uniformly partitioned into a large number of small aged β subgrains during tension, which strongly impedes strain localization that would typically occur across multiple β subgrains in the fashion of long straight slip bands in the case of the RSST samples. Furthermore, the hierarchical α structure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining. These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing high-strength titanium alloys in the precipitation-hardening state.

NiS₂ with high theoretical capacitance shows great potential for supercapacitors (SCs). However, the poor cycling stability and sluggish redox kinetics have limited the development of high-rate NiS₂-based SCs. Integrating materials with high conductivity potentially reinforces its structure and improves its rate capability. 1T-MoS₂ featuring extended interlayer spacing and superior electronic conductivity emerges as an ideal candidate. Therefore, we designed a hybrid material with an alternating interconnected structure of NiS₂ and MoS₂ with adjustable content of 1T-MoS₂. Owing to the improved ion/electron transmittability and the mutual shielding effect, an obvious positive correlation between rate capability and stability with 1T-MoS₂ content was established. The optimized 1T-MoS₂/NiS₂ nanosheets (NMS-2) with 1T phase purity of up to 67.6% in MoS₂ demonstrated exceptional specific capacity (579.4 C g⁻¹ at 1 A g⁻¹) and impressive rate capability (345.0 C g⁻¹ at 30 A g⁻¹), which suggests much faster kinetics compared to pure NiS₂. Notably, the hybrid supercapacitor (HSC) assembled with NMS-2 as the cathode and activated carbon as the anode (NMS-2//AC HSC) exhibited a maximum specific capacitance of 137.4 F g⁻¹ at 1 A g⁻¹. Furthermore, this HSC can deliver a high energy density of 45.9 Wh kg⁻¹ at 774.9 W kg⁻¹, and could retain 17.7 Wh kg⁻¹ even at a high power density of 7731.7 W kg⁻¹. After 5000 cycles at a high current density of 5 A g⁻¹, the HSC still remained 93.23% of its initial capacitance with an extremely low fading rate of 0.0014% per cycle.

Due to the small size, active mobility, and intrinsic softness, miniature soft robots hold promising potentials in reaching the deep region inside living bodies otherwise inaccessible with compelling agility, adaptability and safety. Various materials and actuation strategies have been developed for creating soft robots, among which, ferromagnetic soft materials that self-actuate in response to external magnetic fields have attracted worldwide attention due to their remote controllability and excellent compatibility with biological tissues. This review presents comprehensive and systematic research advancements in the design, fabrication, and applications of ferromagnetic soft materials for miniature robots, providing insights into their potential use in biomedical fields and beyond. The programming strategies of ferromagnetic soft materials are summarized and classified, including mold-assisted programming, 3D printing-assisted programming, microassembly-assisted programming, and magnetization reprogramming. Each approach possesses unique advantages in manipulating the magnetic responsiveness of ferromagnetic soft materials to achieve outstanding actuation and deformation performances. We then discuss the biomedical applications of ferromagnetic soft material-based soft robots (e.g., minimally invasive surgery, targeted delivery, and tissue engineering), highlighting their potentials in revolutionizing biomedical technologies. This review also points out the current challenges and provides insights into future research directions, which we hope can serve as a useful reference for the development of next-generation adaptive miniature robots.

Due to its high electrical conductivity and platinum-like electronic structure, molybdenum phosphide (MoP) has attracted extensive attention as a potential catalyst for the hydrogen evolution reaction (HER) by water splitting. Nevertheless, in the oxygen evolution reaction (OER), the electrocatalytic performance of MoP did not achieve satisfactory results. Therefore, novel nitrogen-doped carbon-encapsulated La-doped MoP nanoparticles (La-MoP@N/C) are synthesized, which show outstanding durability and electrocatalytic activity in both HER and OER. Detailed structural characterization and calculations confirm that La doping not only effectively adjusts the electron density around Mo and P atoms, accelerates the adsorption and desorption processes, but also increases the number of active sites. Low overpotentials of 113 and 388 mV for HER and OER at 10 mA cm^-2 are achieved with the optimized La_0.025-Mo_0.975P@N/C. Furthermore, the two-electrode electrolyzer assembled with La_0.025-Mo_0.975P@N/C also presents impressive water splitting performance. This study indicates that rare earth doping can be used as an efficient strategy to control the local electronic structure of phosphides precisely, which can also be extended to other electrocatalysts.

Self-regulating heating and self-powered flexibility are pivotal for future wearable devices. However, the low energy-conversion rate of wearable devices at low temperatures limits their application in plateaus and other environments. This study introduces an azopolymer with remarkable semicrystallinity and reversible photoinduced solid-liquid transition ability that is obtained through copolymerization of azobenzene (Azo) monomers and styrene. A composite of one such copolymer with an Azo: styrene molar ratio of 9:1 (copolymer is denoted as PAzo_9:1-co-polystyrene (PS)) and nylon fabrics (NFs) is prepared (composite is denoted as PAzo_9:1-co-PS@NF). PAzo_9:1-co-PS@NF exhibits hydrophobicity and high wear resistance. Moreover, it shows good responsiveness (0.624 s⁻¹) during isomerization under solid ultraviolet (UV) light (365 nm) with an energy density of 70.6 kJ kg⁻¹. In addition, the open-circuit voltage, short-circuit current and quantity values of PAzo_9:1-co-PS@NF exhibit small variations in a temperature range of -20 °C to 25 °C and remain at 170 V, 5 μA, and 62 nC, respectively. Notably, the involved NFs were cut and sewn into gloves to be worn on a human hand model. When the model was exposed to both UV radiation and friction, the temperature of the finger coated with PAzo_9:1-co-PS was approximately 6.0°C higher than that of the other parts. Therefore, developing triboelectric nanogenerators based on the in situ photothermal cycles of Azo in wearable devices is important to develop low-temperature self-regulating heating and self-powered flexible devices for extreme environments.

Grain boundaries (GBs) are often known as intergranular cracking sources in alloys at high temperatures, resulting in limited high-temperature strength and ductility. Here, we propose a GB-dual-carbide (denoted as GB-DC) strengthening strategy and have developed a high-performance (NiCoFeCr)₉₉Nb_0.5C_0.5 high-entropy alloy (HEA) with exceptional strength-ductility synergy at 1073 K. Chain-like coherent M₂₃C₆ carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic (FCC) matrix during deformation. Nano-scale NbC particles are distributed alternatively between M₂₃C₆ carbides and inhibit their coarsening. Both strength and ductility of the GB-DC HEA increase dramatically at strain rates ranging from 10⁻⁴ to 10⁻² s⁻¹ at 1073 K, compared with those of the single-phase NiCoFeCr HEA. Specifically, yield strength of 142 MPa, ultimate tensile strength of 283 MPa, and elongation of 34% were obtained, which are twice that of the reference NiCoFeCr HEA (82 MPa, 172 MPa, and 18%, respectively). EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature, and TEM analysis revealed that dislocations can go through the coherent phase boundaries (CPBs) and activate dipoles inner M₂₃C₆ carbides, which weakened the stress concentration in GBs. This substantially reduces the critical stress for dislocation generation and transmission to a stress level lower than that required for intergranular fracture. Theoretical estimation suggests that carbides result in a much higher activation energy (∼510 kJ/mol) for GB sliding and a rather low interface energy (∼101 mJ/m²) compared with the GB energy (1000 mJ/m²), which rationalizes the enhanced GB cohesion by carbides.

Texture formation is frequently observed in parts produced by Laser Powder Bed Fusion (L-PBF), which can induce anisotropy and may potentially degrade plasticity. In this study, we introduce a laser remelting strategy to mitigate these adverse effects. By employing experimental observations and numerical simulations, we established the relationship between melt pool thermal history, variant selection, and mechanical properties. Our results indicate that the strengthening of texture can be prevented by disrupting the variant selection memory effect when there is a difference in scanning speeds between the printing and remelting lasers. The achieved random variant orientation is attributed to the altered cooling rates and temperature gradient directions during solidification across different layers. The optimized Ti-6Al-4V alloy demonstrates high strength (1211.5 ± 13 MPa) and significant elongation (12.3% ± 0.8%), exhibiting a superior strength-ductility synergy compared to samples produced by direct printing or laser remelting with consistent parameters, as well as most reported L-PBF processed Ti-6Al-4V alloys. Our findings provide new insights into phase transformation kinetics in L-PBF of Ti-6Al-4V alloys and facilitate the optimization of this process for manufacturing high-performance components.