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Bionic multifunctional structural materials that are lightweight, strong, and perceptible have shown great promise in sports, medicine, and aerospace applications. However, smart monitoring devices with integrated mechanical protection and piezoelectric induction are limited. Herein, we report a strategy to grow the recyclable and healable piezoelectric Rochelle salt crystals in 3D-printed cuttlebone-inspired structures to form a new composite for reinforcement smart monitoring devices. In addition to its remarkable mechanical and piezoelectric performance, the growth mechanisms, the recyclability, the sensitivity, and repairability of the 3D-printed Rochelle salt cuttlebone composite were studied. Furthermore, the versatility of composite has been explored and applied as smart sensor armor for football players and fall alarm knee pads, focusing on incorporated mechanical reinforcement and electrical self-sensing capabilities with data collection of the magnitude and distribution of impact forces, which offers new ideas for the design of next-generation smart monitoring electronics in sports, military, aerospace, and biomedical engineering.

Materials exhibiting caloric effects can serve as green alternatives in place of the gas refrigerants used in traditional vapor refrigeration systems, which are facing rising energy usage and environmental issues. This study investigates the barocaloric effect of fatty acids, which are typical phase-change materials. Fatty acids exhibit a reversible isothermal entropy change of about 600 J kg−1 K−1 and an adiabatic temperature change of about 10 K at a pressure less than 60 MPa, resulting from the pressure-driven liquid–solid phase transition. In the solid state, the adiabatic temperature change of fatty acids is larger than that of the n-alkanes with similar transition temperatures. Raman analysis indicates that the population of the distorted molecular chains in fatty acids is remarkably decreased when they are transformed from liquid to solid state, leading to the colossal entropy change. For solid fatty acids, the intermolecular interactions characterized by the hydrogen bonds are significantly strengthened under pressure, which explains their large adiabatic temperature change. This study suggests fatty acids are promising refrigerants for eco-friendly barocaloric cooling. [ABSTRACT FROM AUTHOR]

The surface martensite strengthening of ultra‐fine isotropic porous iron has been performed via carburization and quenching treatment at 950 °C for 30 min. This paper is devoted to investigating the evolution of microstructure and related mechanical behavior of porous iron after carburization treatment. Results indicate that an effective carburization thickness (300 µm) contributes to a substantial improvement in compressive ductility (62%) and surface hardness (219 HV0.025) of carburized porous iron. Further, the quenching treatment after carburization produces the porous iron with an ultra‐fine martensite microstructure on surface layer that makes porous iron attain the highest yield strength (256 MPa) and energy absorption capacity (85 KJ kg−1). The major contribution of this present work is a demonstration that an improvement in mechanical properties of ultra‐fine porous iron can be achieved through the carburization and quenching treatment to control the phase structure on surface. Thus, the surface martensite strengthening is considered as a feasible method to prepare more valuable porous iron based alloys, and to provide them with more promising applications on key structural parts. [ABSTRACT FROM AUTHOR]

The Fe–Ni–P–Cu alloys with different copper content (0, 0.5, 1, and 2 wt%) are fabricated by liquid phase sintering (LPS) at 950 °C. The nano‐Cu powder is mechanically mixed for 90 min with Fe–Ni–P composite powder using the ethanol as the medium. The microstructure, microhardness and compressive properties of Fe–Ni–P–Cu alloys are investigated. The results indicate that the copper is beneficial to improve the mechanical properties of sintered specimens. The sample contains a small amount of γ‐(Fe, Ni) phase when the copper content is 1 wt%, which results in its the highest compressive yield strength (948.1 MPa). The highest microhardness of 371 HV is accessible in Fe–Ni–P–Cu alloy with 2 wt% Cu. The fracture surface analysis indicates that sintered specimens with Cu addition exhibit a typical intergranular mode. [ABSTRACT FROM AUTHOR]

The metastable Fe-Ni-P alloy with phosphorus (P) solid-solution structure has been fabricated by spark plasma sintering. Its face-centered cubic (FCC) matrix without the precipitation of phosphide attains a high plasticity and an excellent strain hardening ability at room temperature. This Fe-Ni-P alloy is subjected to cryogenic treatment at various temperatures (−20 °C and −50 °C), to investigate the role of phosphorus on the microstructural evolution and mechanical properties of γ-(Fe-Ni) alloy at low temperatures. The results indicate that the addition of phosphorus can destabilize the Fe-Ni-P alloy and facilitate its martensitic transformation during cryogenic treatment. P-doping does not lead to obvious embrittlement of Fe-Ni-P alloy at low temperatures, but strengthens the alloy by promoting microstructure evolution. The Fe-Ni-P alloy has high plasticity and good strain hardening ability after treated at −20 °C, and is converted to acicular martensite structure after being treated at −50 °C, resulting in a significant increase in its hardness (433 HV) and compressive yield strength (1271 MPa). Developing this Fe-Ni-P alloy as a load-bearing component for low-temperature conditions shows great promise. [ABSTRACT FROM AUTHOR]