A grain-size-dependent structure evolution in gradient-structured(GS) Ni under tension

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.

High entropy ultra-high temperature ceramic thermal insulator(Zr_(1/5)Hf_(1/5)Nb_(1/5)Ta_(1/5)Ti_(1/5))C with controlled microstructure and outstanding properties

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.

A gate-tunable artificial synapse based on vertically assembled van der Waals ferroelectric heterojunction

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.