Under mechanical loading, nanocrystalline metals show unique behaviour, among the most common of which are high strength, mechanically induced grain growth and twin formation. However, mechanically induced grain growth is seldom correlated with twins. Here we report a clear relationship between grain growth and nanoscale twins in 20-nm-thick gold films with a grain size of B19 nm under cyclic loading based on atomic-scale observations and analyses. We find that the formation of nanotwins is an effective way to assist grain coarsening, following a fundamental process that the mutual formation of nanotwins in two neighbouring grains changes the local grain orientation and dissociates the grain boundary into new segments, which become more mobile. The proposed mechanism of nanotwin-assisted grain growth may have important implications for understanding the interface-mediated mechanisms of cyclic plastic deformation and for the interface engineering design of nanostructured metals with both high strength and good fatigue resistance.

Electrochemical actuators play a key role in converting electrical energy to mechanical energy. However, a low actuation stress and an unsatisfied strain response rate strongly limit the extensive applications of the actuators. Here, we report hybrid manganese dioxide (MnO 2 ) fabricated by introducing ramsdellite (R-MnO 2 ) and Mn vacancies into birnessite (δ-MnO 2 ) nanosheets, which in situ grew on the surface of a nickel (Ni) film, forming a hybrid MnO 2 /Ni actuator. The actuator demonstrated a rapid strain response of 0.88% s −1 (5.3% intrinsic strain in 6 s) and a large actuation stress of 244 MPa owing to the special R-MnO 2 with a high density of sodium ion (Na + )-accessible lattice tunnels, Mn vacancies, and also a high Young's modulus of the hybrid MnO 2 /Ni composite. Besides, the cyclic stability of the actuator was realized after 1.2 × 10 4 cycles of electric stimulation under a frequency of 0.05 Hz. The finding of the novel hybrid MnO 2 /Ni actuator may provide a new strategy to maximize the actuating performance evidently through tailoring the lattice tunnel structure and introducing cation vacancies into electrochemical electrode materials.

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Stimulated by the requirement for wearable electronics, crack‐based strain sensors made from polymer‐supported metal films have been reported as a prospective structure for detecting subtle deformation with ultrahigh sensitivity and excellent flexibility. However, the regulation of crack preparation remains a challenge and the use of noble metals retards the large‐scale promotion toward practical application. Here, a cost‐effective strain sensor with ultrahigh strain sensitivity under small strains (ε) is designed based on the submicron to nanoscale voided clusters in Cu‐Al alloy films. The formation of channel cracks in the film is manipulated by regulating the intrinsic microstructure of the film, and the corresponding mechanism is discussed in detail. The strain sensor developed from the cracked Cu‐Al film exhibits ultrahigh gauge factors as high as 584 (0% < ε < 0.5%), 10219 (0.5% < ε < 0.9%), 43152 (0.9% < ε < 1.75%) which is among the highest in reported values. Furthermore, the practical application of the developed sensor in wearable electronics and detection of small deformation is demonstrated. This work provides a novel approach to optimize the sensing performance of flexible strain sensors.

Flexible strain sensors with high sensitivity and high mechanical robustness are highly desirable for their accurate and long‐term reliable service in wearable human‐machine interfaces. However, the current application of flexible strain sensors has to face a trade‐off between high sensitivity and high mechanical robustness. The most representative examples are micro/nano crack‐based sensors and serpentine meander‐based sensors. The former one typically shows high sensitivity but limited robustness, while the latter is on the contrary. Herein, ultra‐robust and sensitive flexible strain sensors are developed by crack‐like pathway customization and ingenious modulation of low/high‐resistance regions on a serpentine meander structure. The sensors show high cyclic stability (10 000 cycles), strong tolerance to harsh environments, high gauge factor (>1000) comparable with that of the crack‐based sensor, and fast response time (<58 ms). Finally, the sensors are integrated into a wearable sign language translation system, which is wireless, low‐cost, and lightweight. Recognition rates of over 98% are demonstrated for the translation of 21 sign languages with the assistance of machine learning. This system facilitates achieving barrier‐free communication between signers and nonsigners and offers broad application prospects in gesture interaction.