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Recent progress in manufacturing now enables the efficient fabrication of complex oxide-glass components at the micrometer– to sub-micrometer scale. This benefits both the industry and fundamental research as such miniature glass parts have numerous applications. However, at these length-scales, the mechanical properties of glasses can no longer be predicted based on bulk material characteristics. Here it is shown that fused silica micro-pillars fabricated by laser-assisted etching are almost ten times stronger than their bulk-sized counterparts. The relatively rough surface typical for this process does not much impair this strength. Additionally, it is demonstrated that annealing of the as-fabricated structures at 1200 °C in air results in significantly smoother surfaces. The accompanying increase in mechanical strength from approximately 8 GPa to 10 GPa is due to the reduction of stress concentrations at the surface, as demonstrated by finite element simulations. It is also demonstrated that the gain in mechanical resistance of glass components due to downsizing occurs already for parts as large as almost 20 µm – orders of magnitude above the critical size reported for other micro-mechanical effects. These micro-mechanical properties of selective laser-assisted etching structured fused silica components are key to a reliable use of glass micro-components.

Based on the gradient hierarchical distribution of vascular bundles of bamboo, a gradient hierarchical multicellular column (GHMC) evolved from the spatial folding was proposed. Crashworthiness analysis of GHMC was carried via Abaqus/Explicit. Results show that the proposed GHMC has better energy absorption ability compared with the square tube under the same thickness or the same mass. The folding wavelength of GHMC is significantly decreased and it can produce more number of folds compared with the square tube. Under the condition of the same mass, the peak crushing force of GHMC decreases meanwhile its energy absorption increase by 10.1% to 72.44% compared with the square tube. Effect of hierarchical level and cell wall thickness on the energy absorption and their deformation mode under different height-length ratio (H/L) and cell wall thickness have been analyzed. Simplified super folding element theory was used to predict the mean crush force of GHMC, and the results were in good agreement with the simulations.

Breast cancer, as the common malignant carcinoma in women, seriously reduces the life quality and increases mortality of female worldwide. Fortunately, insufficient chemotherapy with external photothermal therapy could remarkably improve the therapeutic efficiency of breast cancer. In this work, we proposed a polydopamine (PDA) and tetrasulfide bond co-doped hollowed mesoporous silica nanospheres with Dox loading and surface hyaluronic acid coating for drug leakage avoidance (PhMSON@Dox-HA). After intravenously injected into tumor bearing-mice, this therapeutic agent could effectively target to the tumor site owing to the HA modification. The biocompatible property and GSH-induced decomposition capability endows the precise release of drugs in the cytoplasm of tumor cells. Meanwhile, PDA facilitated the efficient photothermal therapy under 808 nm laser irradiation. Therefore, the synergistic effect of chemo-photothermal therapy possessed most effective tumor eradication ability. Our work exploits the design approach of biocompatible and degradable drug delivery nanocarriers and sheds bright light on the chemotherapy and photothermal therapy combination for the malignant tumor elimination.

Co-Cr-Fe-Ni-Mn high entropy alloys (HEAs) have attracted extensive attention due to their broad cryogenic engineering application potential, reasonable control of alloying elements can significantly improve its mechanical performance. In this work, the effects of Co content on the phase stability and mechanical behavior CoxCrFeNiMnAl0.3 HEAs were investigated. It is found that with the decrease of the Co content, the stability of the face-centered cubic (FCC) solid solution phase in the alloy decreases, resulting in the precipitation of the BCC (body-centered cubic) phase from the FCC phase, thereby obtaining the FCC + BCC dual-phase structure. During annealing, the precipitated BCC phase can effectively suppress the grain growth and recrystallization of the FCC solid solution, forming an ultrafine-grained microstructure. In addition, the Ni-Al type nano-B2 phase can form in the BCC phase under the influence of the negative formation enthalpy during solidification. This micro/nano hierarchical structure can effectively improve the mechanical properties of the alloys. Co0.25CrFeNiMnAl0.3 maintains relatively excellent tensile yield strength (486 MPa), the tensile elongation remains above 20 %. This study regulates the formation of the BCC phase and B2 phase by reducing the content of Co, which provides a new idea for the preparation of low-cost HEAs with excellent mechanical properties.

In contrast with titanium (Ti) alloys, the α+β region for commercially pure Ti is neglectable. Therefore, its β transus (Tβ) can be regarded as a watershed for β-Ti and α-Ti. Utilizing this characteristic, we fabricated dual-textured Ti extrudates through a powder metallurgy route via manipulating the hot extrusion temperature. The crystallographic texture along extrusion direction (ED) was analyzed. Different from the sole //ED texture throughout the entire extrudate in previous studies, our extrudates exhibited unique dual-textured microstructure. The firstly extruded portion manifested //ED and //ED, whereas the rest extrudate displayed //ED. This was attributed to the realtime extrusion temperature of each location in comparison with Tβ. On the other hand, the last portion of the extrudate contained much more interstitial nitrogen and oxygen, which led to extremely high strength via solid solution strengthening. This was resulted from a combination effect of diffusion-controlled element absorbing and material flow during extrusion. Our findings may open up a new direction in developing high-performance materials with variable microstructure and mechanical properties for medical applications like neoarthrosis.

This research reports on the design, fabrication, and multiscale mechanical characterization of flexible, planar mechanical metamaterials with tailorable mechanical properties. The tunable mechanical behavior of the structures is realized through the introduction of orthogonal perforations with different geometric features. Various configurations of the perforations lead to a wide range of Poisson’s ratios (from −0.8 to 0.4), load-bearing properties, and energy absorption capacities. The correlations between the configuration of the perforations and the auxetic response of the structures are highlighted through computational and experimental characterizations performed at multiple length scales. It is demonstrated that the local in-plane rotation of the solid ligaments in a uniaxially loaded structure is the primary factor that contributes to its strain-dependent auxetic behavior at macroscopic scales. Confinement of these local rotations is then used as a practical strategy to activate a self-strengthening mechanism in the auxetic structures. It is further shown that the fabrication of planar flexible structures with controllable Poisson’s ratios is feasible through spatial adjustment of perforations in the structure. Finally, discussions are provided regarding the practical applications of these structures for a new generation of highly energy-absorbing protective equipment.

It is generally believed that the influence of hydrogen on plastic deformation of grain boundaries should be considered when analyzing hydrogen-induced intergranular fracture in polycrystalline metals. In this paper, the equilibrated H distribution around GBs was firstly investigated by employing the grand canonical Monte Carlo method. Then, MD simulations were performed to study the plastic response of GBs under uniaxial tensile loads in different directions, with various bulk H concentrations considered. The results indicate that the influence of H on dislocation nucleation from GB depends on both tensile directions and characteristics of GB structures. Specifically, two dislocation nucleation mechanisms, called dislocation dissociation nucleation (DDN) and heterogeneous dislocation nucleation (HDN), are identified. Careful analyses show that H segregation can increase the energy barrier of DDN, which results in H-inhibited dislocation nucleation. In contrast, the HDN mechanism involves H-enhanced or H-insensitive dislocation nucleation, which mainly depends on the influence of H on GB stress.

A high-priority target in the design of new metallic materials for load-bearing implant applications is the reduction of Young's modulus approximating that of cortical bone in the predominant loading direction. Here, we explore how directionally preferential bulk elastic properties of implant materials are achieved by harnessing elastic anisotropy. Specifically focusing on recently proposed biocompatible refractory high-entropy alloys (RHEAs) in the body-centered cubic structure, we conduct systematic densityfunctional theory calculations to investigate the single-crystal elastic properties of 21 Ti-containing RHEAs. Our results provide evidence that the valence electron count has a dominant influence on elastic anisotropy and crystal directions of low Young's modulus and high torsion modulus in the RHEAs. By means of modeling the orientation distribution function for crystallographic texture, we examine the effect of non-random texture on the anisotropic poly-crystalline Young's modulus and torsion modulus with varying texture sharpness. We adopt fiber textures that can result from rolling and distinct texture orientations that can form during rapid directional solidification. We discuss the potential for lowering Young's modulus in the RHEAs by using single crystals or textured aggregates. Furthermore, we prepare four of the theoretically considered alloys by arc-melting and report their lattice parameters, quasi isotropic Young's moduli, and Wickers hardnesses. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Asphalt rubber (AR) is a sustainable paving material composed of bitumen and crumb rubber modifier (CRM) recycled from waste tires. The interaction between bitumen and CRM re-distributes the bitumen fractions and creates a multiphase internal structure of AR. Although the superior aging resistance of AR has been acknowledged, the aging mechanism of AR remains unclear due to the limited understanding on the behaviors of different phases of AR during aging. This study aims to investigate the structural and mechanical evolution of AR binder during aging through micromechanical back-calculation and experimental tests. A series of separation methods were used to disintegrate the multiphase system of AR at four aging conditions. The mechanical properties of different phases obtained from frequency sweep tests and their volumetric fractions were used as the input for the micromechanical back-calculation, which yielded accurate prediction for the complex modulus of swelling rubber but failed for that of undissolved rubber, so further chemical characterization was conducted to estimate its mechanical evolution. The results indicated that the aging of AR is a process in which internal multiphase structures changed simultaneously with mechanical properties. All subphases became stiffer but their influences on the overall mechanical property of AR variated after aging.

A systematic study was carried out on a novel designed austenitising bending process to explore the effects of quenching temperatures on the evolution of microstructure and mechanical properties of high-strength micro-alloyed steel. Results reveal that the qualified parts could be bent into a satisfactory shape without spring-back and cracks in bending temperatures of 850–1000 °C. The simulation was applied to predict the equivalent stress, stress neutral layer (SNL) and plate thickness. Strength presents a decreasing trend with the increase of bending temperature owing to integrated influences of high-temperature dynamic recovery (DRV) and dynamic recrystallisation (DRX). Beyond that, SNL nearby the geometrical centre line throughout the plate thickness and dislocation pile-ups on the tension/compression zones are responsible for the smaller hardness on middle regions while higher hardness on the surface areas. Through austenite reconstruction, a smaller martensite packet size would directly improve the strength of the plates bent at a lower temperature. The prior austenite size may be related to the appearance of martensite variants but not necessary. Furthermore, the high accuracy by comparing the experimental results with simulation would provide a high-value reference for the practical manufacturing process of railway spring clips.

In the post Moore era, as the size miniaturization approaches limit of the devices, silicon-based sensors cannot meet the requirements of micro/nano sensing with small size and high precision. The piezoelectric sensor based on lithium niobate (LN) single crystal thin film has excellent electromechanical property, photoelectric property, piezoelectric property, which can realize high precision sensing at small size. In our work, 4-inch silicon-based LN single crystal thin film was prepared based on low-temperature bonding technology and chemical mechanical polishing (CMP) method. The oxygen plasma treatment was adopted for increasing the surface hydrophilia to enhance the bonding strength. Grinding parameters under different film thickness were determined by experiments. The parameters of the film was characterized by scanning electron microscope (SEM) with a thickness of 6.294 μm and by atomic force microscope (AFM) obtained the surface roughness is 585 pm. The x-ray diffraction (XRD) test showed that the CMP process could release the compressive stress caused by the bonding, thus obtaining high quality LN single crystal films. The prepared films are polarized and the domain walls can be clearly observed by piezoresponse force microscopy (PFM). It provides a more comprehensive way to prepare ferroelectric domain devices.

This work attempted to introduce high pressure to reduce pore generation in laser welding of selective laser melted AlSi10Mg, which is different from the traditional approach where the vacuum was preferred in laser welding of aluminum alloys. To understand these phenomena, the impacts of laser welding parameters and ambient pressure on the porosity and weld geometry were examined. Porosity ratio was found linearly increasing with the laser power or linear energy. High-speed imaging revealed that the large pores were formed by multiple merging of small pores, which explained the decrease in fine porosity (

Naito K., Kuwahara Y., Yamamoto H., et al. Improvement of acid resistance of Zn-doped dentin by newly generated chemical bonds. Materials and Design, 215, 110412. https://doi.org/10.1016/j.matdes.2022.110412., Dental caries, the world's most prevalent infectious disease, is caused by the diffusion of hydroxyl ions into tooth structures. To prevent dental caries, the application of fluoride (F) and zinc (Zn) ions to teeth surfaces are potential effective measures. In this study, The ionic influence, especially the chemical bond of F and Zn, on the acid resistance of dentin were investigated by particle induced X-ray / gamma-ray emission, X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The results showed Zn was distributed in the limited surface layer of dentin without altering its crystal structure. From the Zn K edge extended X-ray absorption fine structure, Zn incorporated into dentin was surrounded by oxygen and demonstrated four-fold coordination. The bond length and chemical state of Zn–O in Zn doped dentin suggested newly generated Zn–O covalent bond, which may improve acid resistance of dentin. This study showed that the atomic and molecular structures, such as the molecular distances and chemical state, influenced acid resistance of teeth, emphasizing the validity of chemical state analysis for understanding properties in biomaterials.

Herein, we systematically investigate the corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in artificial seawater with various fluoride ion (F−) concentrations and pH values using electrochemical, static immersion measurements and surface characterizations. Results of electrochemical tests manifest that increasing the F− concentration and/or reducing pH value can deteriorate the corrosion performance of Ti80 alloy due to the dissolution of the compact passive film into the porous passive film. Besides, the electrochemical parameters obtained from polarization curves indicate that the F− concentration has few effects on the cathodic reaction but noticeable promoting effects on the anodic process, whereas the increase of pH plays a significant role in inhibiting both cathodic and anodic processes. In addition, surface characterizations reveal the preferential dissolution of the equiaxed α phase compared to the intergranular β phase, resulting from its relatively low Volta potential. We also interpret the F− concentrations and pH values dependent corrosion behaviour based on the mixed potential theory and illustrate the corrosion mechanisms associated with F− in artificial seawater. We believe that the insights into the F− concentration and pH value dependent corrosion behaviour can provide practical guidelines for the design and development of Ti alloys with high-corrosion resistance.

This study focused on a newly developed ultrasonically assisted (UA) wire arc additive manufacturing (WAAM) process for metal matrix nanocomposite of AA7075 with TiB2 nanoparticles. The ultrasonic probe was directly dipped into the local molten pool and traveled behind the arc during deposition. Comprehensive experimental studies were performed and the UA-WAAM sample showed superiorities over conventional WAAM ones in multiple perspectives including a lower number of porosities, refined solidification structure, and less agglomerated nanoparticle distribution under the same deposition parameters. These improved microstructure features led to enhanced mechanical properties of the UA-WAAM samples, as reflected in the tensile tests and hardness measurement results. The benefits of nanoparticles in the formation of equiaxed grain structures and strength contribution was further leveraged by UA based on their better dispersion. The ultrasonic effects on WAAM process can be mainly attributed to the two nonlinear physical phenomena: acoustic cavitation and streaming induced by power ultrasound in molten metal.

Rechargeable metal-air (O2) batteries have been regarded as the promising candidates for wearable and flexible energy devices owing to their outstanding energy density, low cost, and high safety. Generally, the electrocatalyst at air cathode plays a significant role in various metal-air (O2) batteries. As a versatile and efficient technique, electrospinning has been considered as a powerful method to fabricate nanofibers, which hold great potential as bifunctional electrocatalysts for such batteries. Although great progresses have been achieved in improving the electrochemical performance of catalysts in recent years, some critical challenges still maintain. In this review, the advanced electrospun carbon nanofiber-based electrocatalysts for flexible metal-air batteries have been summarized. Then, additional discussions have been included focusing on the advantages and characteristics of different nanofibers and some special requirements for various flexible metal-air batteries. Moreover, some current challenges and future prospects in the development of electrospun carbon nanomaterials for flexible metal-air cathode catalysts have been rationally analyzed.

A multifactorial experimental research on erosion-corrosion behavior of liquid–solid swirling flow in pipeline was carried out by a circulating loop system in combination with a variety of test methods. The analysis of statistical significance reveals that the variation of erosion-corrosion rate is explained by three main effects (velocity, sand size, and sand concentration) and two interactions (velocity/sand size and sand size/sand concentration). An empirical linear regression equation with a R2 value of 0.9043 was established to describe the correlation of erosion-corrosion rate with the test parameters and their interactions. It is concluded by microstructural examination of the working electrode surface that under the condition of liquid–solid swirling flow, cutting and corrosion pits are the primary forms of surface damage. The comparative analysis of erosion-corrosion between swirling flow and non-swirling flow shows that the net effect of swirling flow on erosion-corrosion varies with sand size. The corrosion product analysis by EDS and XPS show the presence of Fe2O3 and CaCO3 under swirling flow and non-swirling flow conditions. Furthermore, the element content analysis of EDS and XPS showed that compared with the non-swirling flow, the oxygen content on the electrode surface under the swirling flow condition increased by 42.42% and 35.06%, respectively.

Shape memory materials draw much attention due to various promising potential applications. This work prepares a novel shape memory composite via grading photo-thermal curing method, which has not yet been reported. Expectedly, it merges advantages of epoxy-based shape memory polymer (EP) and polyvinyl alcohol-based shape memory polymer (PVA), which has applicable stiffness and multi-stimuli responsive performance. The unsatisfactory mechanical properties of most water-driven shape memory polymer (SMP) is expected to be solved by this fabrication strategy, so that the application range of water-driven SMP could be further extended. The synergistic plasticization of PVA and EP dominates water-driven shape memory behavior of this composite. Interestingly, its water-driven shape memory performance is able to be further improved by immersed in HCl/EtOH solution. The glassy-to-rubbery modulus ratio (E′g/E′r) of the PVA/EP-HCl/EtOH is about 650 after immersed in 0.1 mol/L HCl/EtOH for 6 h. In addition, this immersed method also can solve the post curing problem of such cationic photocuring. It is an easy, efficient, economical strategy for improving synergistic water-driven shape memory performance. Furthermore, this shape memory composite is expected to provide new perspective and practical approach to realize the intellectualization of underwater deployment and release structure.

The transition metal carbides have been known to act as traps for hydrogen in steels as well as potential materials for hydrogen storage. Despite numerous experimental and a few theoretical studies, what impacts hydrogen trapping and storage in the transition metal carbides is not well understood. In this work, we use density functional theory to systematically investigate the bulk trapping and storage capabilities of the transition metal carbides. We specifically examine how trapping and storage changes with the transition metal, from the group IVB to group VIB, carbon concentration, and structure. Our results demonstrate a strong correlation between the trap energy and the number of valence electrons in the transition metal, suggesting that the group IVB transition metal carbides are the best carbides for trapping and storage. Hydrogen preferentially sits at octahedral interstices, e.g., the carbon vacancies, in the structure except in certain cases near the Me2C concentration when tetrahedral interstices, devoid of nearest neighbor carbon, can become more favorable. Our results further demonstrate that the lower the carbon concentration, the more hydrogen the transition metal carbide can store. These results demonstrate which carbides will act as the best traps for hydrogen.

Understanding the stored energy release behavior of SiC is crucial for the design of SiC-based fuel cladding for light water reactors because stored energy release affects response during accident conditions. Differential scanning calorimetry was used to evaluate the stored energy of monolithic SiC and SiC fiber–reinforced SiC matrix composite variants following neutron irradiation under light water reactor–relevant dose and temperature conditions. The tests were performed at heating rates of 0.5, 3, and 20 K/min up to 1,273 K. The onset temperature of the energy release roughly corresponded to the irradiation temperature, and energy release was delayed as the heating rate increased. The monolithic and composite specimens exhibited similar stored energy release behavior up to ∼ 1,000 K, and above that temperature, the energy release depended more on material type. The energy release measured in this study is below the material-specific heat capacity at temperatures below ∼1,000 K but exceeds it under certain material and annealing conditions at temperatures above ∼1,000 K. The amount of irradiation-induced volumetric swelling of the specimens was an indication of the total stored energy. Based on this observation, the energy release behavior was described by a swelling recovery model.

Thermoplastic resin is infused into fabric layers to form rigid fiber-reinforced composites (FRCs), which are commonly used for ballistic resistance purposes. Here, we explore the use of patterned thermoplastic hot film as a rapid and straightforward method to laminate plain-weave UHMWPE and demonstrate that these composites have attractive ballistic and stiffness properties. Lamination of 25 layers of fabric using hot press compression lamination of each individual layer with hot film was able to confer the ability to stop 0.357 magnum ammunition shot at 435.9 ± 9 m/s. Patterning the hot film resulted in the composite panels retaining most of their flexibility without losing their ballistic performance compared to when they are laminated with plain (not patterned) hot film. Using the hot film for lamination results in an increase in energy absorption of the laminates with a smaller backface signature and backface volume. These laminates are lighter and more flexible than the commonly used hot resin-infused FRC.

Higher-order deformation theories, such as the couple stress and strain gradient theory, have been widely used to predict the mechanical behavior of micro/nano-scale structures. In this paper, the additional length scale parameter introduced in the couple stress theory is measured by performing bulk-scale tensile and micro-scale cantilever bending experiments. Bulk-scale characterization provided microstructural information of the polycrystalline copper plate along with macroscopic mechanical properties. Micro-scale cantilevers with thicknesses ranging from 1.6 µm to 8.6 µm were fabricated within the copper plate using femtosecond laser machining followed by focused ion beam milling. Line load was applied on these samples utilizing a nanoindenter. Finite element analysis was performed to exclude the effect of substrate deformation. The measured effective elastic modulus increases from 94 GPa to 215 GPa with decreasing thickness. The increase of the bending rigidity is analyzed based on the couple stress theory, and the length scale parameter is measured as 0.78 µm. The physical origin of the length scale parameter is discussed by considering mobile dislocations escaping via the free surfaces during loading.

The presence of TiC in Ti alloys is ubiquitous, so, for the interest of exploring its effects, carbon is added in Ti-5553 (beta phase alloy). After fabrication, sintering and multi heat treatments are done to get desired microstructure (TiC in beta, alpha and alpha-matrix). Quasi-static compression, three-point bend test, nano-indentation, and abrasion tests are conducted to study the microstructural response. Different analyzing tools such as SEM, EDS, EBSD, and HRTEM are used to examine microstructural changes before and after fracture. Results showed that TiC crystals are hard and brittle, and favorite sites for crack nucleation and propagation. After comparing both the curves and their corresponding micrographs, it is concluded that the propagation speed of the crack is much faster in TiC as compared to the beta and alpha phases. Furthermore, an increase in the value of strain upon reaching a crack at the TiC/Tiᵦ, and TiC/Tiα interface justifies that these phases offer comparatively more toughness and ductility. In addition, the presence of these crystals in the beta phase initiate fracture almost within half of the elastic limit of Ti-5553 beta phase alloy. Conclusively, TiC has an adverse effect on titanium's mechanical properties if shape and size are not controlled.

High precision lattice structure (LS) shows great potential applications in aerospace, acoustic, biomedical, and wearable products due to its multifunctional characteristics and excellent mechanical properties. Inspired by lightweight, high-strength, and high-stability glass sponges (GSs), a unique circle-/grid-like heterogeneous glass sponge lattice structure (GSLS) was successfully designed and manufactured by selective laser melting (SLM) with Ti6Al4V alloy. Compared with the commonly used body-centred cubic (BCC), face-centred cubic (FCC), honeycomb and diamond LSs, GSLS displays the strongest compressive properties (E = 1560 MPa, σmax = 40 MPa, σy0.2 = 34 MPa, W = 5.95 J). The normalised elastic modulus and normalised compressive strength of GSLS are almost 1.4 and 1.3 times, 2.6 and 2.4 times, 2.7 and 3.5 times, 18 and 8.3 than that of FCC, BCC, honeycomb, and diamond LSs, respectively. Most importantly, unlike the 45° diagonal shear failure of homogeneous BCC and FCC, the FEA simulation reveals that the heterogeneous unit cell in GSLS can enhance the strut connectivity, disperse the stress, and exhibits a unique fracture mechanism of cell-after-cell and layer-by-layer. The fracture mechanism of GSLS can improve the load-bearing capability, maintain strength, and protect its interior and entire integrity during compression.

Hexagonal boron nitride (h-BN) is an excellent thermally conductive and electrically insulative material. However, the formation of heat transfer pathways of h-BN in thermal interface materials is restricted due to its poor aqueous dispersity. Herein, water-soluble lignosulfonate (LS) is used to promote the dispersion of h-BN, the phenolic hydroxyl and three-dimensional structure of LS could form hydrogen bonding or steric hindrance with h-BN under ultrasound treatment. After mixing with cellulose nanofiber (CNF), the three-dimensional thermally conductive pathways are built in LS-BN/CNF aerogel through freeze-drying. The results show that the through-plane thermal conductivity of LS-BN/CNF/PVA composite with 0.2 wt% LS (LS0.2-BN/CNF/PVA) exceeds 1.22 W/mK when the h-BN/CNF ratio is 3:1 (w/w), which is 6.1-fold of that of PVA film (0.20 W/mK). The initial decomposition temperature and tensile strength of LS0.2-BN/CNF/PVA composite are 205 °C and 38.5 MPa, respectively, demonstrating acceptable thermal stability and mechanical properties for electronics as thermal interface and packing material. Overall, this work put forwards an effective approach to disperse h-BN and paves the way in developing high-performance thermal interface materials.

Groove, as a special structure at the front of solid–liquid (S/L) interface, takes a great influence on the distribution of impurities for silicon. In this work, the interaction between grooves and impurities was studied, and the evolution model of groove was proposed. It has been found that the crystal growth rate and the impurity content in the groove determine the evolution behavior of the groove. Correspondingly, the migration behavior of impurities in groove with solidification was studied and the mathematical model was proposed to describe the anomalous enrichment phenomenon. This work is helpful to understand the distribution behavior of impurities in micro-zone such as groove and make a theoretical foundation for the deep removal of impurities.

Weak layer interface is a non-negligible issue in the domain of cement additive manufacturing, which results in lacking integrity, mechanical inferiority and deteriorated durability. In order to overcome these disadvantages, a silicate-based interface strengthening agent (ISA) is herein designed to penetrate into layer interface and generate a dense precipitation phase (hydrated calcium silicate gel) from the reaction with portlandite, a weak phase with lower mechanical properties. Through this enhancing strategy, both horizontal and vertical layer interface exhibit remarkable bonding strength higher than that of matrix material, turning the intrinsic weak interface to a “robust interface”. The strengthening mechanism is attributed to the modification of interfacial hydration products and the densification of multi-scaled pore structure at interface region, which is demonstrated via synthetical characterizations along with molecular dynamics simulations. This interface strengthening method based on silicate penetration and precipitation provides a convenient and effective approach to preparing robust layer interface stronger than its cement matrix.

Two nano-scaled hexagonal distortions in high temperature BCC phase during cooling is commonly observed in many alloys systems. Although efforts have been made on studying the lattice softening of the BCC structure during cooling, the distortion mechanisms are less addressed. Thus, the formation of two hexagonal structures in the β precipitates in a Cu-40Zn alloy treated by ECP was thoroughly investigated. Results show that the β precipitates contain two kinds of nano-sized and diffuse atomic clusters one with a η structure obeying the Burgers OR and the other a ω structure obeying the Blackburn OR. They were each formed through a two-stepped atomic displacement. For the η structure, the first step is the atomic shuffle of each second 110β plane in the β direction and the second is a structure change mainly by a {1 1¯ 2} β shear. For the ω structure, the first is an atomic shuffle on each second and third {112¯}β plane in the ± [111]β directions and then normal strains in three mutually perpendicular directions. The concomitant formation of the two structures minimizes the lattice distortion of single formation. The present results provide new information on the formation mechanism of the two hexagonal structures in a BCC matrix.

The power supply to the sensors becomes increasingly critical as the Internet of Things (IoT) evolves. Hence, our goal is to transform ambient environmental energy in our daily lives into electrical energy and then give power to IoT sensors. In this work, we developed and manufactured functionally-graded piezocomposite using poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] and barium titanate (BaTiO3, BTO) particles. Functionally graded materials offer better specific strength, toughness, and fatigue resistance than homogeneous composite materials, making them appropriate for energy-harvesting. Spin coating and hot-pressing methods were used to create BTO/P(VDF-TrFE) composites with varying BTO particle fractions and structures. After determining the optimal spin coating and hot-pressing conditions, the composites were polarized using the corona poling technique. The structure and properties of the composites were determined by scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. Then the piezoelectric characteristics were tested, and impact and vibration energy production tests were devised and carried out. This research provides a feasible manufacturing method for functionally graded piezocomposites and investigates the material energy-harvesting potential. Meanwhile, guidance is offered for the construction of functionally graded piezoelectric composites structures for use in various types of energy-harvesting applications.

This work proposes a novel technique to address the detrimental effect of high loading of halogen-free flame retardants (FRs) on foaming of polymer composites. This is the first time nano-fibrillation is applied to tailor FR composites for foam applications with desired microcellular structure. As highlight of this work, the presence of polytetrafluoroethylene (PTFE) nanofibrils serves multiple roles by compensating for reduced foaming behavior of highly-filled matrix, and contributing to enhancing FR efficiency and stiffness. Inclusion of 1 wt% nanofibrils in polystyrene (PS) filled with 30 wt% expandable graphite (EG), tunned melt rheological properties leading to improving cell density up to two orders of magnitude. The average cell size of the foam also decreased from 103 μm to 10 μm, with respect to PS/EG, improving compressive strength and modulus. The entangled PTFE nanofibrils transformed the fluffy char layer into a dense one, preventing matrix disintegration and dripping to meet UL94-V0. This was confirmed by reduced fire growth rate (FIGRA), peak heat release rate (PHRR) and peak smoke production rate (PSPR) in cone calorimetry. The unique characteristics of this composite make it promising for fabricating FR polymeric foams for various applications including automotive, aerospace, electronics and construction, necessitating high fire safety level.

To meet the need for an environmentally friendly fouling-release coating with high mechanical strength and good adhesion to substrates, a four-component nanocomposite was developed by a simple and industrially applicable blending approach. The nanocomposite consists of mechanically stable matrix polythiourethane (PTU), 1 wt% low surface free energy and rubber-like polydimethylsiloxane (PDMS), 1 wt% lubricant silicone oil, and 1 wt% tetrapodal shaped micro-nano ZnO (t-ZnO) filler particles, hereafter named PPZO. The rubber-like PDMS formed microdomains at the PTU/air interface, while silicone oil was distributed between the PDMS microdomains. The tensile strength of PPZO nanocomposite was approximately 63 MPa, two to four hundred times higher than the tensile strength of previously reported oil-modified coatings. The adhesion strength of PPZO to the substrate was 30 times higher than that of pure PDMS. After a five-month dynamic field test, the PPZO surface revealed much less biofouling than the references (AlMg3 and PTU), confirming its long-term biofouling control property. The attached algae on PPZO could easily and completely be removed by gentle brush cleaning. The good biofouling control property of PPZO can be attributed to the increased water repellency (signified by the increased water contact angle) and the surface slippage by silicone oil incorporation.

Diamond-like carbon (DLC) has excellent performance but cannot be directly applied in gears and bearings due to poor adhesion. A novel gradient composite layer that includes a hardened nitrided layer and a self-lubricating DLC structure at the outermost surface was fabricated on M50 steel via plasma-assisted thermochemical treatment. The structure evolution of the modified layer was comprehensively characterized by optical microscopy, scanning electron microscope (SEM), atomic force microscopy (AFM), transmission electron microscope (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that the nanoparticles embedded in the DLC structure gradually increase until the nitrided diffusion layer. The DLC structure is like being anchored in the nitrided layer by nanoparticles carbide/nitride. The inner of the pre-nitrided layer is hardly affected during the plasma carburizing process. The gradient structure is verified to endow the treated samples with functionally graded hardness profile and super wear resistance by Vickers hardness tester, Nano-indentation tester, and pin-on-disk tribometer. The composite layer's tribological behavior was discussed through wear scar morphology observation by SEM and chemical structure in tracks with Raman spectroscopy. This method proposes a promising way for self-lubricating layer application in the steel matrix without complex operation and high economic cost.

3D highly porous architectures with tailored flexibility along with dimensional stability are currently an emerging area due to a wide range of technological applications. We have highlighted here the importance of mechanical and thermal stability of the building blocks and interfacial bonding for development of such scaffolds. 2D electrospun free-standing nanofibrous mats of polyethylene terephthalate (PET) with different molecular weights were used to study the properties of basic foundation units. The nanohybrid shish-kebab (NHSK) type polycaprolactone (PCL) crosslinked networks were grown between the stacked nanofibrous mat for better bindings among the layers. Carbon nanotubes were further introduced into PET nanofibers as well as in binder envelop layers in order to insight into the properties of thermal and structural stability. The presence of different confined 1D nucleating surface like nanotubes and nanofibers gives us the opportunity to study interpenetrating NHSK lamellae at different length scale. A range of crosslinked scaffold microstructures by origami route were investigated to highlight the importance of process design for fabrication of dimensionally robust porous geometries.

In this study, we present a novel process to fabricate diamond-metal laminates. By means of successive chemical vapor deposition and physical vapor deposition processes, the lamellar material is deposited layer by layer on silicon wafers. Laminates consisting of two, five and ten layers of diamond were realized. In addition, fabrication of diamond-based, biomimetic brick-and-mortar structures was successful for the first time. For this purpose, diamond layers of a five-layer laminate were structured by laser cutting into hexagonal platelets with diameters of 400 µm and 800 µm. The mechanical behavior was characterized by three-point bending. Mostly spontaneous failure with little crack deflection was observed, indicating a strong diamond-metal interface. At over 1250 MPa, the laminates exhibit nominal strengths that exceed those of other lamellar ceramic-metal composites by at least a factor of two, while fracture energy lies in a medium range. The laminates with segmented diamond layers exhibit damage tolerance.

Selective laser sintering has been used to manufacture different structural variations of a pre-buckled circular honeycomb. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic impact loading. Pre-buckled circular honeycombs with aspect ratios e = 0.8 and e = 0.6 were compared to a traditional, straight-walled honeycomb. It has been found that the mechanical behaviour of the honeycomb can be tailored to yield different mechanical responses. Principally, decreasing the aspect ratio reduced the stress at yield, as well as the total energy absorbed until densification, however, this alleviated the characteristic stress-softening response of traditional honeycombs under static and dynamic conditions. When subjected to multiple cycles of loading, a stabilised response was observed. The numerical response closely agreed with the experimental results. A simplified, periodic boundary condition model also closely agreed with the experimental results whilst alleviating computational run time by nominally 75%. The numerical full factorial parameter design sweep identified a broad range of mechanical behaviour. This represents a valuable tool to identify optimal design configurations for future impact mitigating applications.

Enrichment of exosomes with high structural and functional integrity is a critically important step before downstream applications in biological and clinical domains. In this work, dynamic biological interfaces functionalized fructose-responsive immunomagnetic beads (Fr-IMBs) were fabricated by incorporating the dynamic biological interfaces composed of dopamine and 4-carboxyphenylboronic acid with immunomagnetic beads. These fabricated Fr-IMBs were successfully applied to capture the MCF-7 exosomes with a high capture efficacy of 91.0%. After incubation with fructose, the molecular structure of the dopamine-boronic acid complexation can be rearranged and the antibody (anti-CD63) bound exosomes were released competitively, with a yield greater than 79.8%. Those exosomes that underwent both immunomagnetic separation and fructose triggered release remained their good bioactivity to promote MCF-7 cell migration. Better yet, exosomes enriched by Fr-IMBs possessed higher purity and better preservation of tumor-related molecular information of the exosomal proteins than those obtained through the ultracentrifugation approach, as proved by the comparative proteomics. These proposed sugar-responsive immunomagnetic beads may serve as biofriendly candidates in enriching useful biomarkers (e.g., cells, nucleic acids, proteins, etc.) efficiently from complex biological samples with high purity.

3D printed medical titanium alloy has shown great advantages in manufacturing complex and personalized scaffolds for tissue engineering. To promote the repair of bone defects, fabrication of a scaffold with high accuracy and excellent cell behaviors is required. However, the partially melted or un-melted powders must be removed in the post-process. In this study, the effects of unfused metal powders on the biocompatibility of 3D printed Ti alloy scaffolds were analyzed by co-culture with MC3T3-E1 cells and RAW 264.7 cells, and the surface treatment strategy was proposed. Results showed that surface treatment can enhance the biocompatibility of the 3D printed Ti alloy scaffolds. The vitro tests with MC3T3-E1 cells demonstrated that the ETi5Cu (etched Ti5Cu) showed the better cell proliferation and osteogenic potential, and the lower cell apoptosis rates. Moreover, higher concentration of powders showed inhibitory effects on cytocompatibility and osteogenesis of MC3T3-E1 cells, and promoted the polarization of macrophages to M1 type. In summary, the removal of metal powders on the 3D printed scaffolds plays an important role in the biological performance, which provided a promising strategy for the application of Ti implants.

The desire for increased performance and functionality has introduced additional complexities to the design and fabrication of additively manufactured (AM) parts. However, addressing these needs would require improved control over local properties using in-line feedback from fast-acting low-fidelity models during the fabrication process. In this regard, differential evaporation is an inherent characteristic in metal AM processes, directly influencing local chemistry, material properties, functionality, and performance. In the present work, a differential evaporation model (DEM) is presented for laser powder bed fusion (LPBF) AM to predict and control the effect of evaporation on chemistry and properties on local and part-wide scales. The DEM model is coupled with an analytical thermal model that is calibrated against 51.2 Ni [at%] nickel titanium shape memory alloy (NiTi SMA) single-track experiments and a multi-layer model that accounts for the AM part’s multi-layer design and the inherent melt pool overlap and chemistry propagation. The combined hierarchical model, consisting of the thermal, evaporation, and multi-layer components, is used to predict location-specific chemistry for LBPF AM fabrication of Ni50.8Ti49.2 [at%] SMAs. Model predictions are validated with values obtained from multi-layer experiments on a commercial LPBF system, resulting in a root mean square error (RMSE) of 0.25 Ni [at%] for predicted Ni content. Additionally, martensitic transformation temperature, Ms, is calculated and compared with empirical data, resulting in an RMSE of 18.6 K. A practical account of the cumulative and propagative thermal-induced evaporation effect on location-specific chemistry is made through this linkage of models. Fundamentally, this model chain has also provided a solution to the forward modeling problem, enabling steps to be taken towards resolving the inverse design problem of determining processing parameters based on desired location-specific properties.

Predicting mechanical properties of graphene-reinforced metal matrix nanocomposites (GRMMNCs) usually requires atomistic simulations that are computationally expensive without scalability or micromechanics-based models (such as widely used Halpin-Tsai model) that may lead to considerable errors in many cases. This paper first combines molecular dynamic (MD) simulation and machine learning (ML) techniques to predict the mechanical properties of graphene reinforced aluminium (Gr/Al) nanocomposites and use them to modify Halpin-Tsai model. Extensive MD results for Young’s modulus and ultimate tensile strength of Gr/Al nanocomposites are obtained, with the intricate effects of graphene’s volume fraction, alignment angle, chirality and environment temperature being taken into account. After training and optimization based on MD data, ML models are developed with the capability in estimating Young’s modulus and ultimate tensile strength. The micromechanics based Halpin-Tsai model is then modified by using the Young’s modulus predicted by both MD and ML models such that the Young’s modulus can be readily determined with significantly improved accuracy from an explicit relationship that is very easy to use in the analysis and engineering design of Gr/Al nanocomposite structures.

Estimations of bulk hardness from nanoindentation are frequently subject to considerable uncertainties due to indentation size effects (ISE), pileup effects, and potential influence of surface quality or test methods. This study examined materials science principles of nanoindentation test methods to enable accurate prediction of bulk hardness for a series of high purity Fe and Fe-(3–25 wt%) Cr alloys. These materials were tested in as-annealed and thermally aged (100–900 h at 475 ℃ to produce Cr-rich α’ precipitates) conditions. Nanoindentation with a Berkovich indenter at constant strain rate (0.05–0.5 /s) and constant loading rate conditions provided comparable bulk equivalent hardness (H0) extracted by Nix-Gao model, indicating a weak strain rate sensitivity at room temperature. Results from electropolished and fine mechanically polished samples gave comparable measured hardness. Pileup corrections produced a 5–14% correction to H0 which agreed with the experimental bulk Vickers hardness within ∼10% for most tested materials. The microstructural model-predicted and measured strength values agreed for aged samples. A derived analytic expression demonstrates that an ISE error, associated with inappropriate methods such as hardness ratios or changes at a reference depth, would be as large as 60% in estimated bulk hardness for the investigated Fe-Cr alloys.

Photoresists play an important role in the electronic information industry; however, traditional photoresists have disadvantages including severe volume shrinkage, low precision, and poor adhesion. Here, a combined free radical / cationic dual-curing dry film photoresists (DFRs) for 405 nm photolithography was developed based on functional acrylic resins containing oxetane pendant groups. The acrylic resins were successfully synthesized by free radical copolymerization of methyl methacrylate, methacrylic acid, ethyl methacrylate and 3-ethyl-3-(methacryloyloxy)methyloxetane. The structure and properties of resins were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. The resins could undergo cationic photopolymerization to generate a film with good mechanical and thermal properties. Notably, the prepared DFRs showed excellent comprehensive performances including outstanding pattern transfer ability with a high resolution of 20 μm, high photosensitivity, high contrast, satisfactory developing speed, and good adhesion to the substrate. Such oxetane-containing acrylic resins may have potential application in high-performance DFRs.

Magnesium (Mg)-based composites have recently been studied as biodegradable material for the fabrication of orthopedic implants. Nevertheless, in physiological environments, proper mechanical properties and sufficient degradation rate are needed. In this paper, zinc (Zn) was uniformly distributed in the magnesium matrix using a ball milling process, and then the composite of Mg-3Zn/xfCNTs (x = 0, 0.2, 0.4, and 0.8 wt%) was successfully fabricated using a combination of semi-powder metallurgy, sintering and extrusion processes for use as a biodegradable load-bearing implant. The influence of functionalized carbon nanotubes (fCNTs) content on compressive strength, corrosion behavior and in vitro bioactivity (apatite formation ability and cytocompatibility) of the composite was investigated. The key toughening mechanisms that resist crack propagation include fCNTs pull-out, grain bridging by fCNTs, Crack branching and crack deflection. Furthermore, electrochemical and in-vitro immersion studies demonstrated that the corrosion behavior of Mg-3Zn composite under high concertation encapsulation was slightly reversed by fCNTs. Furthermore, cell culture investigations revealed that MG-63 cells present high level of cell viability and proliferate, implying that Mg-3Zn/0.4fCNTs composites are cytocompatible. All the findings suggest that the Mg-3Zn/0.4fCNTs composite with outstanding mechanical properties and appropriate corrosion resistance and biocompatibility may be a potential candidate for biodegradable implant application.

We performed first-principles calculations to determine the effects of 14 metallic solutes on twin boundary (TB) energy and strength/embrittlement in Ti alloys, with Ti {1 0 1¯ 2} and {1 0 1¯ 1} TBs as models. Twin formation energies were calculated to identify the effects of solutes on TB stability. Segregation energy and the associated segregation concentration and solubility energy were examined to identify the existence states of the solutes. The influences of solutes on TB strength were identified through strengthening/embrittling energy and its mechanical and chemical contributions. Tensile tests were performed using the “uniaxial-strain loading” and the “uniaxial-stress loading” methods to determine maximum TB strength.

Poorly functioning scaffold materials and limitations in material-cell construction technology remain problems in bone tissue engineering. Electrospinning has been proven to be a suitable and available technique for production of 3D biomimetic scaffolds. To overcome these problems and retain the advantages of electrospinning, bioelectrospinning has been proposed to provide guidance by micropattern, homogeneous cell distribution, and effective nutrient utilization. Herein, we fabricated poly (3-hydroxybutyrate-co-4-hydroxybutyrate)/poly (vinyl alcohol) (P34HB/PVA) with human bone mesenchymal stem cells (hBMSCs) to biomimetic core-shell microfiber/cells complex by coaxial bioelectrospinning. Characterization of the fiber materials revealed that coaxial electrospinning combined the advantages of the two materials. In vitro cellular assays showed that after bioelectrospinning, the cells and material could be simultaneously spun while maintaining cell activity. The material provided a good 3D microenvironment allowing cell adhesion, proliferation, and differentiation. Both the in vitro and in vivo tests indicated the formation of mineralized nodules in both the co-spun and co-axial groups, while the implants formed bone-like tissue after 16 weeks of implantation. This study shows that coaxial bioelectrospinning technology can be used to construct tissue-engineered bone. Our technique might be applied in the future to fabricate more complex tissue and organs.

Astrocyte activation is an important cause of neuropathic pain. Inhibiting the hyperactivation of astrocytes is beneficial to control over neuropathic pain. However, there is a lack of non-pharmaceutical ways to inhibit the hyperactivation of astrocytes. This study aimed at regulating the activity of glial cells via the architecture of 3D porous scaffolds. Herein, the 3D porous scaffolds with co-continuous and oriented pores were prepared via solid-phase stretching of co-continuous polymer blends followed by selective phase extraction. Compared to the isotropic scaffold, the proliferation of astrocytes slowed down on the oriented scaffolds. Meanwhile, the expression of growth factors and inflammatory factors secreted by astrocyte activation was inhibited by the oriented pores. It led to the suppression of the Wnt/β-catenin signaling pathway that is crucial to determine chronic neuropathic pain. Immunofluorescence staining displayed that the hyperactivation of astrocytes was inhibited, and the expression of kindlin-1, a key protein that activates astrocytes, was downregulated. The proposed strategy offers a probable physical means to relieve neuropathic pain.

The macroscale mechanical properties of dissimilar joints are generally influenced by the fracture behavior of joint interface. However, little is known about the dominant factor for the joint properties related with both macroscale fracture behavior and microscale interfacial properties. Herein, microscale tensile testing of the joint interface was coupled with the macroscale fracture evaluation to elucidate the dominant factor of strength in dissimilar joints between 6061 aluminum alloy and high tensile strength galvannealed steel via friction stir spot welding (FSSW). Microstructural analyses revealed the characteristic formation of interfacial microstructure accompanied by friction and Zn discharge during the FSSW process. Microscale tensile testing was performed on the specimen on which the pre-notch was introduced to induce local fracture at the intended position on the joint interface. Results showed the presence of the weakest interface attributed to initial joining defects formed by Zn concentration at the outer area, which were consistent with the outside of the crack arresting area confirmed by macroscale evaluation. These results indicated that the joint strength of dissimilar joints between 6061 aluminum alloy and galvannealed steel is dominated by the local strength of the joining area without defects and suggested a process design for improving dissimilar joints.

In this study, a relatively light and high strength high entropy alloy thermoelectric material (Al2CoCrFeNi) for extreme service conditions was prepared by arc melting method. We find that the microstructure of the high entropy alloy (HEA) can be changed by annealing. By the tuning of proper annealing process, the microstructure evolution of the HEA can be adjusted to improve its mechanical and TE properties. Ultimate compressive strength can reach about 1.3 GPa after 1000 ℃ annealing. Fine-grain and precipitation strengthening are the main reasons for the improvement of the mechanical properties. The conductivity, Seebeck coefficient and thermal conductivity are all affected by grain size, precipitates, structural complexity and so on. The present work provides an effective means of preparing and regulating microstructures for the energy-conversion technique, and also supplies a feasible reference for the future development of lightweight, high-strength HEA TE materials.

New resorbable Ca32Mg12Zn38Yb18-2xBxAux (x = 1,2) alloys were designed and prepared in order to verify their use for medical applications as potential short-term implants. Their amorphous structure containing some crystalline phases (CaZn, CaZn2 and MgZn) was determined by X-ray and neutron diffraction and electron microscopy methods. The biocorrosion behavior of the plates was tested by hydrogen evolution measurements, immersion, electrochemical polarization tests, and electrochemical impedance spectroscopy in Ringer’s solution at 37 C. The corrosion analysis was also supplemented by X-ray diffraction, photoelectron, and ICP-AES spectroscopy. The corrosion resistivity measurements revealed that the alloys manifest enhanced corrosion resistance. The corrosion current density for Ca32Mg12Zn38Yb18- 2xBxAux (x = 1, 2) alloys were 18.46 and 8.79 lA/cm2, which is lower than for pure Mg (47.85 lA/cm2) and Zn (33.96 lA/cm2). A decreasing tendency for hydrogen to evolve as a function of time was noted. The hydrogen evolution did not exceed 1 ml/cm2 over 1 h and average corrosion rate is calculated as 0.32 g/m2 . h for Ca32Mg12Zn38Yb14B2Au2 alloy after 312 h. The corrosion mechanism of the alloys includes an anodic dissolution, a hydroxide precipitation, corrosion product layer formation and corrosion propagation stage.

The uniformity of a recoated powder layer affects the performance of parts manufactured by SLM directly, while it is related to the characteristics of spatters. The small spatter moves pretty fast, while the low optical transmittance in the spectrum of a hot spatter in the coaxial optical path of SLM equipment prevents clear imaging of this target with high contrast. In this study, a coaxial optical path with an enhanced optical transmittance is used for imaging the melt pool and its surrounding phenomena simultaneously. An experimental system was developed using a high-speed camera for coaxial observation of hot spatters in the SLM process. The problems of limited field of view and high measurement uncertainty of an off-axis process monitoring system are solved. For defocused and distorted spatter images, both a segmentation algorithm and an object detection method have been proposed and proved to be effective. It was found that the direction and strength of the local airflow field could be estimated via the curvature of the spatter trajectory. More importantly, the quantity of spatters detected is positively related to the amount of powder locally distributed on the baseplate, which is useful to estimate the powder bed thickness at this position.

Refractory complex concentrated alloys are an emerging class of materials that attracts attention due to their stability and performance at high temperatures. In this study, we investigate the variations in the mechanical and thermal properties across a broad compositional space for the refractory MoNbTaTi quaternary using high-throughput ab-initio calculations and experimental characterization. For all the properties surveyed, we note a good agreement between our modeling predictions and the experimentally measured values. We reveal the particular role of molybdenum (Mo) to achieve high strength when in high concentration. We trace the origin of this phenomenon to a shift from metallic to covalent bonding when the Mo content is increased. Additionally, a mechanistic, dislocation-based description of the yield strength further explains such high strength due to a combination of high bulk and shear moduli, accompanied by the relatively small size of the Mo atom compared to the other atoms in the alloy. Our analysis of the thermodynamics properties shows that regardless of the composition, this class of quaternary alloys shows good stability and low sensitivity to temperature. Taken together, these results pave the way for the design of new high-performance refractory alloys beyond the equimolar composition found in high-entropy alloys.