Microstructure of TA2/TA15 graded structural material by laser additive manufacturing process

TA2/TA15 graded structural material（GSM） was fabricated by the laser additive manufacturing（LAM） process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The results show that the TA2 part of exhibiting near-equiaxed grains was Widmanst？tten α-laths microstructure. The TA15 part containing large columnar grains was fine basket-weave microstructure. The graded zone was divided into four deposited layers with 3000 μm in thickness. As the distance from the TA2 part increases, the alloy element contents and the β phase volume fraction increase, the α phase volume fraction decreases and the microstructure shows the evolution from Widmanst？tten α-laths to basket-weave α-laths gradually. The micro-hardness increases from the TA2 part to the TA15 part due to the solid solution strengthening and grain boundary strengthening.

Microstructure and mechanical properties of TA15/TC11 graded structural material by wire arc additive manufacturing process

A graded structural material(GSM)with a material transition from TA15 to TC11 was fabricated by wire arc additive manufacturing(WAAM)method.The grain morphology,chemical composition,microstructure and mechanical properties of the as-deposited GSM were all characterized to investigate their variations along the deposition direction.The results indicate that from TA15 to TC11,the grain size decreases and a transition from columnar grains to equiaxed grains occurs.The content of alloy element alters greatly within a short distance,and the width of the mutation zone is 800μm.Both TA15 and TC11 regions exhibit basketweave microstructure withα-phase andβ-phase.However,during the transition from TA15 to TC11,theα-lath becomes fine,which leads to an increase in microhardness.The tensile test shows that the bonding strength at the interface is higher than the longitudinal strength of TA15,and the lateral elongation at the interface is higher than that of TA15 and TC11.

Point Defect Phenomena of Crystalline Structure in Some Common Structural Materials

The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materials. Point defect theory has been widely applied in material mineralization research, unfavorable transformation controlling, material modification, the research and development of new materials and so on. Point defect theory is one of the important theories for new material research and development. Herein we mainly discuss the application of point defect theory in some structural material researches.

A review of the strengthening–toughening behavior and mechanisms of advanced structural materials by multifield coupling treatment

The application of an external field is a promising method to control the microstructure of materials, leading to their improved performance. In the present paper, the strengthening and toughening behavior of some typical high-performance structural materials subjected to multifield coupling treatment, including electrostatic field, electro-pulse current, thermal field, and stress field, are reviewed in detail. In addition to the general observation that the plasticity of materials could be increased by multi-external fields, strength enhancement can be achieved by controlling atomic diffusion or phase transformations. The paper is not limited to the strengthening and toughening mechanisms of the multifield coupling effects on different types of structural materials but is intended to provide a generic method to improve both the strength and ductility of the materials. Finally, the prospects of the applications of multi-external fields have also been proposed based on current works.

CERAMICS AS CANDIDATE STRUCTURAL MATERIALS FOR CRYOGENIC APPLICATIONS

The use of zirconia-based ceramic materials as smpport materidls for superconducting magnets and in cryopenic engineeriny generally has been considered. The relationship between compsition and mechanical properties at cryogenic temperature has also been investigated.

Activation characteristics of candidate structural materials for a near-term Indian fusion reactor and the impact of their impurities on design considerations

Activation analyses play a vital role in nuclear reactor design.Activation analyses,along with nuclear analyses,provide important information for nuclear safety and maintenance strategies.Activation analyses also help in the selection of materials for a nuclear reactor,by providing the radioactivity and dose rate levels after irradiation.This information is important to help define maintenance activity for different parts of the reactor,and to plan decommissioning and radioactive waste disposal strategies.The study of activation analyses of candidate structural materials for near-term fusion reactors or ITER is equally essential,due to the presence of a highenergy neutron environment which makes decisive demands on material selection.This study comprises two parts; in the first part the activation characteristics,in a fusion radiation environment,of several elements which are widely present in structural materials,are studied.It reveals that the presence of a few specific elements in a material can diminish its feasibility for use in the nuclear environment.The second part of the study concentrates on activation analyses of candidate structural materials for near-term fusion reactors and their comparison in fusion radiation conditions.The structural materials selected for this study,i.e.India-specific Reduced Activation Ferritic-Martensitic steel（IN-RAFMS）,P91-grade steel,stainless steel 316 LN ITER-grade（SS-316 LN-IG）,stainless steel 316 L and stainless steel 304,are candidates for use in ITER either in vessel components or test blanket systems.Tungsten is also included in this study because of its use for ITER plasma-facing components.The study is carried out using the reference parameters of the ITER fusion reactor.The activation characteristics of the materials are assessed considering the irradiation at an ITER equatorial port.The presence of elements like Nb,Mo,Co and Ta in a structural material enhance the activity level as well as the dose level,which has an impact on design considerations.IN-RAFMS was shown to be a more effective low-activation material than SS-316 LN-IG.

Study of GaAs/GaAlAs Multilayer Structural Materials by Electrolyte Electroreflectance

Electrolyte electroreflectance (EER) has been widely employed to investigate the electronic energy band structure and related physical properties of semiconductors. The electrolyte electroreflectance (EER) method combined with electrochemical anodic dissolution was used to study GaAs/GaAlAs multilayer structural materials. According to variation of the EER spectra during anodic dissolution the characteristics of GaAs/GaAlAs multilayer structural materials such as properties of the interface, p-n junction positions and Al content profiles were obtained.

A Research on Harmonious Dialogues with Low Structural Materials in Regional Games for Children

The use of low structural materials can accentuate the characteristics of openness advocated by regional creation.Therefore,when selecting regional game materials,preschool teachers should focus on open and low structures as well as actively and reasonably guide the child’s game behavior,so that each child can make full and efficient use of these materials.At the same time,in a harmonious dialogue with these materials,they are given the opportunity to express what they see,hear,feel,and think in their own ways.

Time lapse in situ X-ray imaging of failure in structural materials under cyclic loads and extreme environments

Damage evolution characterization and performance evaluation under realistic conditions are essential to ensure reliable operation of critical safety components.However,previous studies focus on the surface detection because of very limited penetration capacity of nondestructive testing facilities.Here,we review the recent progress of material damage mechanism by various in situ testing rigs that are compat-ible with laboratory and synchrotron radiation X-ray facilities.Then,taking metallic alloys and composites as model materials,we demonstrate the unique advantages of in situ X-ray three-dimensional tomography in unveiling complex failure mechanisms,quantifying crack growth driving forces and crack closure phenomena,and elucidating the strengthening/degrading effects from microstructure and environment on structural material degradation.Finally,we also discuss the ongoing direction of in situ multi-scale visualization and characterization with the development of advanced high-energy X-ray facilities,the improvement of in situ devices and sample environments,the demand of high-throughput tests,and the processing and application of massive test data.

The electromagnetic response of composition-regulated honeycomb structural materials used for broadband microwave absorption

The undesirable absorption bandwidth is the main limitation for the application of microwave absorbing materials.Noting that the design of structure and composition of absorbing coating allows it to obtain a satisfying absorption bandwidth and to avoid weight increasing,honeycomb and its sandwich structures coated by various absorbant have been developed and measured using an arch measurement system over2-18 GHz.To further understand the absorption mechanisms of honeycomb structural materials,simulation based on finite element method and transmission line theory is performed to analyze the different responses to the applied microwave between honeycomb structural materials and uniform-medium slab materials.The proper composition design allows control over the microwave loss mechanisms,which optimize the coating to possess both of the dielectric and magnetic advantages.For the honeycomb structural materials,the magnetic resonation is found for the first time,which is resulting from the periodic honeycomb walls on both sides of the dielectric cavity(consisting of the aramid paper interlayer and vacuum hexagonal prisms).In addition,the conversion of structure from solid to honeycomb brings about changes in impedance,propagating path,effective wavelength,effective attenuation area,microwave phases,and inductive coupling effect,etc.,which result in a better microwave absorbing performance.The honeycomb sandwich structure coated by CIP/CB/EP with the weight ratio of 4:0.03:1 shows the absorption bandwidth of~9.8 GHz for reflection loss(RL)lower than-10 dB which covers part of the S and C bands and almost the whole X and Ku bands.

Connecting microscopic structure and macroscopic mechanical properties of structural materials from first-principles

Computer simulation plays a critical role in connecting microscopic structure and macroscopic mechanical properties of structural material,which is a key factor that needs to be considered in design of such kind of material.Via the quantum mechanics first-principles calculations,one can gain structure,elastic constant,energetics,and stress of selected material system,based on which one is able to predict the mechanical properties or provide useful insights for the mechanical properties of the materials.This can be done either directly or in combination with the empirical criterions.This paper reviews the recent research advances on the attempts to predict the mechanical properties of structural materials from first principles.

Evaluation of mechanical properties of structural materials by a spherical indentation based on the representative strain-an improved algorithm at great depth ratio

At great depth ratio, two methodologies based on the representative strain were improved to extract mechanical properties of metallic engineering structural materials from P-h curve of an indentation response. The improved aspects include： the com- bination of great ratio h1/R=0.1 and h2/R=0.4 replaced h1/R=0.01 and h2/R=0.06 （Cao＇s method） and h1/R=0.1 and h2/R=0.3 （Ogasawara＇s method）; three types of metallic engineering structural materials with obviously different elastic modulus were dealt with to get their calculation parameters, respectively; a new parameter reflecting the effect of work-hardening exponent n was introduced to get the dimensionless function which is independent of n and a relationship between W/（h3σrS） and E^＊/（σrS） at great depth ratio. By using the results of finite element simulation, the efficiency and accuracy of the improved method have been proved, and it showed that the accuracv of the improved method is much better than the former method.

Hot Spot in Materials with Structural Defects under High Shear Loading Rates

The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.

Design,preparation,application of advanced array structured materials and their action mechanism analyses for high performance lithium-sulfur batteries

Lithium-sulfur battery(LSB)has brought much attention and concern because of high theoretical specific capacity and energy density as one of main competitors for next-generation energy storage systems.The widely commercial application and development of LSB is mainly hindered by serious“shuttle effect”of lithium polysulfides(Li PSs),slow reaction kinetics,notorious lithium dendrites,etc.In various structures of LSB materials,array structured materials,possessing the composition of ordered micro units with the same or similar characteristics of each unit,present excellent application potential for various secondary cells due to some merits such as immobilization of active substances,high specific surface area,appropriate pore sizes,easy modification of functional material surface,accommodated huge volume change,enough facilitated transportation for electrons/lithium ions,and special functional groups strongly adsorbing Li PSs.Thus many novel array structured materials are applied to battery for tackling thorny problems mentioned above.In this review,recent progresses and developments on array structured materials applied in LSBs including preparation ways,collaborative structural designs based on array structures,and action mechanism analyses in improving electrochemical performance and safety are summarized.Meanwhile,we also have detailed discussion for array structured materials in LSBs and constructed the structure-function relationships between array structured materials and battery performances.Lastly,some directions and prospects about preparation ways,functional modifications,and practical applications of array structured materials in LSBs are generalized.We hope the review can attract more researchers'attention and bring more studying on array structured materials for other secondary batteries including LSB.

Atomically self-healing of structural defects in monolayer WSe_(2)

Minimizing disorder and defects is crucial for realizing the full potential of two-dimensional transition metal dichalcogenides(TMDs) materials and improving device performance to desired properties. However, the methods in defect controlcurrently face challenges with overly large operational areas and a lack of precision in targeting specific defects. Therefore,we propose a new method for the precise and universal defect healing of TMD materials, integrating real-time imaging withscanning transmission electron microscopy (STEM). This method employs electron beam irradiation to stimulate the diffusionmigration of surface-adsorbed adatoms on TMD materials grown by low-temperature molecular beam epitaxy (MBE),and heal defects within the diffusion range. This approach covers defect repairs ranging from zero-dimensional vacancydefects to two-dimensional grain orientation alignment, demonstrating its universality in terms of the types of samples anddefects. These findings offer insights into the use of atomic-level focused electron beams at appropriate voltages in STEMfor defect healing, providing valuable experience for achieving atomic-level precise fabrication of TMD materials.

DEVELOPMENT OF A MATERIALS RISK INFORMATION PLATFORM FOR A SAFE SOCIETY

A Materials Risk Information Platform is being developed under the cooperation of companies and academic societies with NIMS as project core. To combine safety and economy, which are sometimes contrary to each other, it is important to find an optimal solution using a new concept: risk based engineering. A 5-year project, the Materials Risk Information Platform, was started in 2001 in NIMS on the boilers of thermal power plants and the objectives of this project, research areas and its present state were outlined.

Improving the damage potential of W-Zr reactive structure material under extreme loading condition

Projectiles made of reactive structure materials(RSM)can damage the target with not only kinetic but also chemical energy,but the enhanced damage potential of RSM may become compromised if extreme loading condition disintegrates the projectile before the target is reached.In this work,a ductile coating of Ni was introduced to a tungsten-zirconium(W-Zr)alloy,a typical brittle RSM,to preserve the damage potential of the projectile.Detonation driving tests were carried out with X-ray photography and gunpowder deflagration driving tests were carried out with high-speed photography for the coated and uncoated RSM samples,respectively.The craters on the witness target were analyzed by scanning electron microscopy and X-ray diffraction.The Ni coating was found to effectively preserve the damage potential of the W-Zr alloy under extreme loading conditions,whereas the uncoated sample fractured and ignited before impacting the target in both detonation and deflagration driving.The crack propagation between the reactively brittle core and the ductile coating was analyzed based on the crack arrest theory to mechanistically demonstrate how the coating improves the structural integrity and preserves the damage potential of the projectile.Specifically,the Ni coating envelops theW-Zr core until the coated sphere penetrates the target,and the coating is then eroded and worn to release the reactive core for the projectile to damage the target more intensively.

Coverless Information Hiding Based on the Molecular Structure Images of Material

The traditional information hiding methods embed the secret information by modifying the carrier,which will inevitably leave traces of modification on the carrier.In this way,it is hard to resist the detection of steganalysis algorithm.To address this problem,the concept of coverless information hiding was proposed.Coverless information hiding can effectively resist steganalysis algorithm,since it uses unmodified natural stego-carriers to represent and convey confidential information.However,the state-of-the-arts method has a low hidden capacity,which makes it less appealing.Because the pixel values of different regions of the molecular structure images of material(MSIM)are usually different,this paper proposes a novel coverless information hiding method based on MSIM,which utilizes the average value of sub-image’s pixels to represent the secret information,according to the mapping between pixel value intervals and secret information.In addition,we employ a pseudo-random label sequence that is used to determine the position of sub-images to improve the security of the method.And the histogram of the Bag of words model(BOW)is used to determine the number of subimages in the image that convey secret information.Moreover,to improve the retrieval efficiency,we built a multi-level inverted index structure.Furthermore,the proposed method can also be used for other natural images.Compared with the state-of-the-arts,experimental results and analysis manifest that our method has better performance in anti-steganalysis,security and capacity.

Advances in the structure design of substrate materials for zinc anode of aqueous zinc ion batteries

Aqueous zinc ion batteries(AZIBs) demonstrate tremendous competitiveness and application prospects because of their abundant resources,low cost, high safety, and environmental friendliness. Although the advanced electrochemical energy storage systems based on zinc ion batteries have been greatly developed, many severe problems associated with Zn anode impede its practical application, such as the dendrite formation,hydrogen evolution, corrosion and passivation phenomenon. To address these drawbacks, electrolytes, separators, zinc alloys, interfacial modification and structural design of Zn anode have been employed at present by scientists. Among them, the structural design for zinc anode is relatively mature, which is generally believed to enhance the electroactive surface area of zinc anode, reduce local current density, and promote the uniform distribution of zinc ions on the surface of anode. In order to explore new research directions, it is crucial to systematically summarize the structural design of anode materials. Herein, this review focuses on the challenges in Zn anode, modification strategies and the three-dimensional(3D) structure design of substrate materials for Zn anode including carbon substrate materials, metal substrate materials and other substrate materials. Finally, future directions and perspectives about the Zn anode are presented for developing high-performance AZIBs.

Measurement of pore diffusion factor of porous solid materials

Internal diffusion of molecules in porous materials plays an important role in many chemical processes.However, the pore diffusion capacity of porous materials cannot be measured by conventional catalyst characterization methods. In the present paper, a pore diffusion factor, the ratio of the diffusionconstriction factor to the pore tortuosity of the porous materials, was proposed to measure the diffusion ability of pores inside solid materials, and a method was proposed for measuring the diffusion factor using a well-defined and uniform pore size material as a reference. The diffusion factor was calculated based on the effective diffusion coefficients and the diffusion-constriction factor and pore tortuosity of the reference porous materials. The pore diffusion factor measurement can be performed at room temperature and atmospheric pressure. The pore diffusion factor of conventional porous materials was found to be much smaller than 1, indicating that there is a lot of room for improving the diffusion ability of the conventional catalysts and adsorbents, and could be significantly increased through adding small number of fibers into the conventional porous materials as template.