Due to advancements of hypersonic vehicles,ultra-high temperature thermal insulation materials are urgently requested to shield harsh environment with superhigh heat flux.Toward this target,ultra-high temperature cera...Due to advancements of hypersonic vehicles,ultra-high temperature thermal insulation materials are urgently requested to shield harsh environment with superhigh heat flux.Toward this target,ultra-high temperature ceramics(UHTCs)are the only choice due to their excellent capability at ultra-high temperatures.We herein report a novel highly porous high entropy(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C fabricated by foam-gelcasting-freeze drying technology combined with in-situ pressureless reaction sintering.The porous(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C exhibited ultra-high porosity of 86.4%-95.9%,as well as high strength and low thermal conductivity of 0.70–11.77 MPa and 0.164–0.239 W/(m·K),respectively.Specifically,Si C sintering additive only locates at the pit of the surface of sintering neck between UHTC grains,and there is no secondary phase or intergranular film at the grain boundary.Besides,the oxidation resistance of high entropy carbide powders is greatly improved compared with that of the mixed five carbide powders.This work clearly highlights the merits of highly porous high entropy(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C as an ultra-high temperature thermal insulation material.展开更多
This work outlines an experimental investigation of grain-size-dependent structure evolution under tension in nickel with a grain size gradient.Two opposite and competing processes,grain refinement and coarsening,were...This work outlines an experimental investigation of grain-size-dependent structure evolution under tension in nickel with a grain size gradient.Two opposite and competing processes,grain refinement and coarsening,were examined within one specimen,due to the widely ranging grain size in gradient-structured(GS)Ni.A tensioninduced minimum grain size of approximately 280 nm was determined in GS Ni,which is comparable to those obtained by severe plastic deformation processes.The minimum grain size was phenomenologically explained using a dislocation model.Below the minimum grain size,the Ni’s grain coarsening ability peaked at approximately 50 nm and progressively decreased with decreasing grain size,showing an inverse grain-size-dependent coarsening tendency.Moreover,this inverse grain coarsening behavior was related to a transition in the deformation mechanism,through which the deformation process was accommodated more by partial dislocation than by full dislocation below a critical grain size.This was confirmed by observation of the microstructure and low temperature tensile testing results.This work demonstrates a high-throughput strategy for exploring the minimum grain size and grain-size-dependent coarsening in metals.展开更多
Memtransistor,a multi-terminal device that combines both the characteristics of a memristor and a transistor,has been intensively studied in two-dimensional layered materials(2 DLM),which show potential for applicatio...Memtransistor,a multi-terminal device that combines both the characteristics of a memristor and a transistor,has been intensively studied in two-dimensional layered materials(2 DLM),which show potential for applications in such as neuromorphic computation.However,while often based on the migration of ions or atomic defects in the conduction channels,performances of memtransistors suffer from the poor reliability and tunability.Furthermore,those known 2 DLM-based memtransistors are mostly constructed in a lateral manner,which hinders the further increasing of the transistor densities per area.Until now,fabricating non-atomic-diffusion based memtransistors with vertical structure remains challenging.Here,we demonstrate a vertically-integrated ferroelectric memristor by hetero-integrating the 2 D ferroelectric materials CuInP_(2)S_(6)(CIPS)into a graphite/CuInP_(2)S_(6)/MoS_(2)vertical heterostructure.Memristive behaviour and multi-level resistance states were realized.Essential synaptic behaviours including excitatory postsynaptic current,paired-pulse-facilitation,and spike-amplitude-dependent plasticity are successfully mimicked.Moreover,by applying a gate potential,the memristive behaviour and synaptic features can be effectively gate tuned.Our findings pave the way for the realization of novel gate-tunable ferroelectric synaptic devices with the capability to perform complex neural functions.展开更多
The pronounced brittleness of hard Laves phase intermetallics is detrimental to their tribological properties at room temperature.In this study,we utilized a heterogeneous structure to engineer an ultrastrong dual-pha...The pronounced brittleness of hard Laves phase intermetallics is detrimental to their tribological properties at room temperature.In this study,we utilized a heterogeneous structure to engineer an ultrastrong dual-phase(Laves+B2)AlCoFeNiNb high-entropy alloy that exhibits a low wear rate(3.82×10-6 mm3/(N·m))at room temperature.This wear resistance in the ball-on-disc sliding friction test with the counterpart of Al2O3 balls stems from the activated deformation ability in the ultrafine Laves lamellae under heterogeneous interface constraints.Furthermore,as tribological stress intensifies,the surface deformation mechanism transitions from dislocation slip on the basal and pyramidal planes to a unique combination of local shear and grain rotation within the Laves phase.Our study illuminates fresh perspectives for mitigating the embrittling effect of Laves phase intermetallics under tribological loading and for the development of wear-resistant materials.展开更多
基金financial support from the National Key R&D Program of China(No.2017YFB0703201)Liao Ning Revitalization Talents Program(No.XLYC2002018)。
文摘Due to advancements of hypersonic vehicles,ultra-high temperature thermal insulation materials are urgently requested to shield harsh environment with superhigh heat flux.Toward this target,ultra-high temperature ceramics(UHTCs)are the only choice due to their excellent capability at ultra-high temperatures.We herein report a novel highly porous high entropy(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C fabricated by foam-gelcasting-freeze drying technology combined with in-situ pressureless reaction sintering.The porous(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C exhibited ultra-high porosity of 86.4%-95.9%,as well as high strength and low thermal conductivity of 0.70–11.77 MPa and 0.164–0.239 W/(m·K),respectively.Specifically,Si C sintering additive only locates at the pit of the surface of sintering neck between UHTC grains,and there is no secondary phase or intergranular film at the grain boundary.Besides,the oxidation resistance of high entropy carbide powders is greatly improved compared with that of the mixed five carbide powders.This work clearly highlights the merits of highly porous high entropy(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C as an ultra-high temperature thermal insulation material.
基金financial support received from the National Key Research and Development Program of China(Grant no.2017YFB0702003)the National Natural Science Foundation of China(Grant no.51471165).
文摘This work outlines an experimental investigation of grain-size-dependent structure evolution under tension in nickel with a grain size gradient.Two opposite and competing processes,grain refinement and coarsening,were examined within one specimen,due to the widely ranging grain size in gradient-structured(GS)Ni.A tensioninduced minimum grain size of approximately 280 nm was determined in GS Ni,which is comparable to those obtained by severe plastic deformation processes.The minimum grain size was phenomenologically explained using a dislocation model.Below the minimum grain size,the Ni’s grain coarsening ability peaked at approximately 50 nm and progressively decreased with decreasing grain size,showing an inverse grain-size-dependent coarsening tendency.Moreover,this inverse grain coarsening behavior was related to a transition in the deformation mechanism,through which the deformation process was accommodated more by partial dislocation than by full dislocation below a critical grain size.This was confirmed by observation of the microstructure and low temperature tensile testing results.This work demonstrates a high-throughput strategy for exploring the minimum grain size and grain-size-dependent coarsening in metals.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.12104462 and 62104134)support from the China Postdoctoral Science Foundation(Grant No.2021M700154)support from the Young Scholars Program of Shandong University。
文摘Memtransistor,a multi-terminal device that combines both the characteristics of a memristor and a transistor,has been intensively studied in two-dimensional layered materials(2 DLM),which show potential for applications in such as neuromorphic computation.However,while often based on the migration of ions or atomic defects in the conduction channels,performances of memtransistors suffer from the poor reliability and tunability.Furthermore,those known 2 DLM-based memtransistors are mostly constructed in a lateral manner,which hinders the further increasing of the transistor densities per area.Until now,fabricating non-atomic-diffusion based memtransistors with vertical structure remains challenging.Here,we demonstrate a vertically-integrated ferroelectric memristor by hetero-integrating the 2 D ferroelectric materials CuInP_(2)S_(6)(CIPS)into a graphite/CuInP_(2)S_(6)/MoS_(2)vertical heterostructure.Memristive behaviour and multi-level resistance states were realized.Essential synaptic behaviours including excitatory postsynaptic current,paired-pulse-facilitation,and spike-amplitude-dependent plasticity are successfully mimicked.Moreover,by applying a gate potential,the memristive behaviour and synaptic features can be effectively gate tuned.Our findings pave the way for the realization of novel gate-tunable ferroelectric synaptic devices with the capability to perform complex neural functions.
基金supports from the National Natural Science Foundation of China(Grant nos.52371068,51931003,52301157,and 52001165)Natural Science Foundation of Jiangsu Province,China(Grant nos.BK20200475 and BK20220965)+2 种基金Jiangsu Funding Program for Excellent Postdoctoral Talent(Grant no.2022ZB251)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant no.XDB0470101)the Fundamental Research Funds for the Central Universities(Grant nos.30921011215 and 30922010401).
文摘The pronounced brittleness of hard Laves phase intermetallics is detrimental to their tribological properties at room temperature.In this study,we utilized a heterogeneous structure to engineer an ultrastrong dual-phase(Laves+B2)AlCoFeNiNb high-entropy alloy that exhibits a low wear rate(3.82×10-6 mm3/(N·m))at room temperature.This wear resistance in the ball-on-disc sliding friction test with the counterpart of Al2O3 balls stems from the activated deformation ability in the ultrafine Laves lamellae under heterogeneous interface constraints.Furthermore,as tribological stress intensifies,the surface deformation mechanism transitions from dislocation slip on the basal and pyramidal planes to a unique combination of local shear and grain rotation within the Laves phase.Our study illuminates fresh perspectives for mitigating the embrittling effect of Laves phase intermetallics under tribological loading and for the development of wear-resistant materials.
