High-cycle fatigue induced twinning in CoCrFeNi high-entropy alloy processed by laser powder bed fusion additive manufacturing

High-cycle fatigue (R=0.1, room temperature) induced microstructural evolution in a laser powder bed fusion (L-PBF) additively manufactured quaternary CoCrFeNi high-entropy alloy (HEA) was studied. The as-built material exhibited a combined and texture and high proportion of low-angle boundaries. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that deformation twinning occurred under the high-cycle fatigue of σmax= 450 MPa (Nf=1.06 ×105), but not for the stress level of 300 MPa and 200 MPa. The deformation twins led to the cyclic softening, as manifested by the continuous increase of maximum strain under the stress-controlled fatigue, and the hardness increased by ∼80 HV0.2 in the post-fatigued condition. EBSD revealed that both the and orientations were favorable for the twin formation. Given that the size of grains with the and orientations was twice larger than those of the other orientations, the grain size effect on twin formation could play a certain role. High-resolution TEM revealed that the full dislocations, lattice distortion, stacking faults, and partial dislocations were associated with the twin, cellular and labyrinth wall-like dislocation structures. The underlying mechanism for the formation of nano-twins during high-stress fatigue involved the dissociation of 1/2 full dislocations to 1/6 partial ones. Moreover, the dislocation cell structure as observed in the as-built condition evolved into sub-grains after the high-cycle fatigue loading, with the immensely dense dislocations at the sub-grain boundary

Modeling of cavity nucleation, early‐stage growth, and sintering in polycrystal under creep–fatigue interaction

A mechanistic-based cavitation model that considers nucleation, early-stage growth, and sintering under creep–fatigue interaction is proposed to predict the number density of cavities ρ. Both the nucleation and early-stage growth rates, controlled by grain boundary (GB) sliding under tension, are formulized as a function of local normal stress σn. Cavity sintering that occurs during the compression is governed by the unconstrained GB diffusion depending on the σn. Modeling results provide important insights into experimental load-waveform design. First, test with initial compression promotes higher ρ compared to the initial tension, if the unbalanced hold time in favor of tension is satisfied. Second, the ρ value does not have a monotonic dependence on either the compressive hold time or stress, because of their competing effect on nucleation and sintering. Third, the optimum value of stress variation rate exists in terms of obtaining the highest ρ value due to sintering effect

Modeling of cavity nucleation, early‐stage growth, and sintering in polycrystal under creep–fatigue interaction

A mechanistic-based cavitation model that considers nucleation, early-stage growth, and sintering under creep–fatigue interaction is proposed to predict the number density of cavities ρ. Both the nucleation and early-stage growth rates, controlled by grain boundary (GB) sliding under tension, are formulized as a function of local normal stress σn. Cavity sintering that occurs during the compression is governed by the unconstrained GB diffusion depending on the σn. Modeling results provide important insights into experimental load-waveform design. First, test with initial compression promotes higher ρ compared to the initial tension, if the unbalanced hold time in favor of tension is satisfied. Second, the ρ value does not have a monotonic dependence on either the compressive hold time or stress, because of their competing effect on nucleation and sintering. Third, the optimum value of stress variation rate exists in terms of obtaining the highest ρ value due to sintering effect

Tuning Electrical and Mechanical Properties of Metal–Organic Frameworks by Metal Substitution

Metal–organic frameworks (MOFs), synthesized by the self-assembly of organic ligands and metal centers, are structurally designable materials. In the current study, first-principles calculation based on density functional theory (DFT) was performed to investigate the intrinsic mechanical and electrical properties and mechanical–electrical coupling behavior of MOF-5. To improve the conductivity of MOF-5, homologous elements of Cu, Ag, and Au were adopted to replace the Zn atom in MOF-5, reducing the band gap and improving its electrical performance. Cu-MOF-5 and Au-MOF-5, with stable structures, exhibit better conductivity. The intrinsic mechanical properties such as independent elastic constants of MOF-5 and M-MOF-5 (M = Cu, Ag, Au) were obtained. MOF-5 and Cu-MOF-5 were experimentally synthesized to demonstrate the reduction in the band gap after metal substitution. The study of the strain effect of MOF-5 and Cu-MOF-5 proves that strain engineering is an effective method to regulate the band gap and this modulation is repeatable. This study clarifies the tunability of the band gap of MOF-5 with metal substituents and provides an efficient strategy for the development of new types of MOFs with desired physical properties using the combination of theoretical prediction and experimental synthesis and validation

Direct wire writing technique benefitting the flexible electronics

This work proposes a rapid manufacturing technique for the conductive lines applied in flexible electronics, which is referred to as the ‘direct wire writing (DWW)’ technique. The fine metal wire is dragged out of the needle by adhesion, and attached to the stick-on substrate synchronously along design paths to form high-quality circuits. This technique overcomes the unstable performance of ink-based conductive lines fabricated by screen printing, spraying, 3D printing, etc., and avoids complex processes for stable metallic circuits mainly manufactured by the photolithography method, etc. Firstly, the forming mechanism of dominating the micro deformation behaviour (local-debonding, slip, warping) is clarified and analysed, which provides guidelines for fabricating in-plane wire patterns and 3D structural circuits rapidly and easily. Subsequently, some practical applications, including strain rosette, wearable sensor patch and light display are presented, showing the promising potential of the DWW technique in the ongoing exploration of flexible electronics.</p

Acid-Interface Engineering of Carbon Nanotube/Elastomers with Enhanced Sensitivity for Stretchable Strain Sensors

Stretchable strain sensors with high sensitivity or gauge factor (GF), large stretchability, and long-term durability are highly demanded in human motion detection, artificial intelligence, and electronic skins. Nevertheless, to develop high-sensitive sensors without sacrificing the stretchability cannot be realized using simple device configurations. In this work, an acid-interface engineering (AIE) method was proposed to develop a stretchable strain sensor with high GF and large stretchability. The AIE generates a layer of SiOx at the interface between the carbon nanotube (CNT) film and Ecoflex, playing a key role in enhancing the sensor’s GF. Compared to devices without AIE (GF = 2.4), the ones with AIE are significantly improved. At an AIE time of 10 min, the GF up to 1665.9 is achieved without sacrificing the stretchability (>100%). The AIE-generated cracks are found to modulate the electrical behaviors and enhance the GFs of sensors with AIE through the crack-induced rapid reduction in the electrical conduction pathway, which is manipulated by the CNTs bridging over the cracks. The device with AIE proves its high mechanical durability through a cycling test (>10 000 cycles) at a high strain up to ∼80%, further paving its practical applications in various human motion detections

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors