Crystalline Microstructure Research Articles

Influence of the Content of Ni as Minority Alloying Element on the Microstructure and Mechanical Properties of Amorphous and Ultrafine Crystalline Al-Cu-Mg-Ni Alloys

Influence of the Content of Ni as Minority Alloying Element on the Microstructure and Mechanical Properties of Amorphous and Ultrafine Crystalline Al-Cu-Mg-Ni Alloys

Targeted Stimulation of Micropores by CS2 Extraction on Molecular of Coal.

The targeted stimulation of micropores based on the transformation of coal's molecular structure is proposed due to the chemical properties and difficult-to-transform properties of micropores. Carbon disulfide (CS2) extraction is used as a targeted stimulation to reveal the internal evolution mechanism of micropore transformation. The variations of microcrystalline structures and micropores of bituminous coal and anthracite extracted by CS2 were analyzed with X-ray diffraction (XRD), low-temperature carbon dioxide (CO2) adsorption, and molecular simulation. The results show that CS2 extraction, with the broken chain effect, swelling effect, and aromatic ring rearrangement effect, can promote micropore generation of bituminous coal by transforming the microcrystalline structure. Furthermore, CS2 extraction on bituminous coal can decrease the average micropore size and increase the micropore volume and area. The aromatic layer fragmentation effect of CS2 extraction on anthracite, compared to the micropore generation effect of the broken chain effect and swelling effect, can enlarge micropores more remarkably, as it induces an enhancement in the average micropore size and a decline in the micropore volume and area. The research is expected to provide a theoretical basis for establishing reservoir stimulation technology based on CS2 extraction.

Parametric Modelling of the Crystalline Microstructure of the MCM41-Type Mesoporous Silica Modified with Derivatives of Alkyls.

A siliceous material in which a framework order was established with a surfactant with sixteen carbon atoms in alkyl chains, MCM-41-C16, was synthesised, surface-modified, and tested regarding the selected physical properties. The pristine material was extracted in an acidic aqueous alcohol and then lined with different surface groups. The properties of four adsorbents were investigated using XRD, X-ray photoelectron spectroscopy, and N2 physisorption techniques. The unit-cell constant was determined from X-ray diffractograms, being in fixed relation to the edge length of the hexagonal frame. The specific surface areas of mesopores and whole crystallites were determined from low-temperature N2-physisorption isotherms. The novelty of this work is a mathematical model of a crystalline microstructure explaining the sizes and shapes of crystalline grains in relation to adsorption features, proposed and successfully tested with the aforementioned experimental data. The roughness of the surface is different from one that is necessary to explain the experimental characteristics quantitatively.

Investigation on Anti-Fuel Erosion Performance of Sasobit/SBS-Modified Asphalt and Its Mixtures.

The fuel leakage of fuel vehicles will exacerbate the occurrence of distresses on asphalt pavements, including peeling, chipping and potholes, especially under the synergistic effect of traffic load and environment. In this research, Sasobit, which is commonly used as a warm agent in asphalt, is selected as the anti-fuel erosion agent and incorporated into SBS-modified asphalt and its mixtures. Diesel and gasoline are selected as the fuel erosion media. Sasobit/SBS-modified asphalt binder and its mixtures are investigated for fuel erosion. The rheological properties of bitumen and the mechanical properties of asphalt mixtures are assessed. The experimental findings show that the dissolution velocity of SBS-modified asphalt with 3% Sasobit is 0.2%/min for diesel erosion, while it is 1.7%/min for gasoline erosion, lower than the control sample without Sasobit. Meanwhile, the rutting factor of Sasobit/SBS-modified asphalt decreases less than that of the control sample without Sasobit. Furthermore, the mass loss ratio after the Cantabro test of Sasobit/SBS-modified asphalt mixtures is 1.2% for diesel erosion, while it is 6.8% for gasoline erosion, lower than that of the control sample without Sasobit. The results of the mechanical properties for asphalt mixtures demonstrate that Sasobit can enhance the anti-fuel erosion performance. Moreover, the research results of the Sasobit modification mechanism show that Sasobit can form a microcrystalline structure in SBS-modified asphalt, which subsequently improves the anti-fuel of asphalt and its mixtures. This research provides a reference for anti-fuel erosion assessment methods and solutions to improve the anti-fuel erosion of asphalt pavement.

Effect of Preparation Process on the Microstructure and Characteristics of TiAl Pre-Alloyed Powder Fabricated by Plasma Rotating Electrode Process

TiAl pre-alloyed powder is the foundation for additive manufacturing of TiAl alloys. In this work, TiAl pre-alloyed powder was prepared using a plasma rotating electrode process (PREP). The effects of electrode rotating speeds and current intensity on the microstructure and characteristics of TiAl pre-alloyed powder have been investigated in detail. The results show that the electrode rotating speeds mainly affected the average particle size of the powder (D50). As the electrode rotating speed increased, the D50 of the powder decreased. The current intensity mainly affected the particle size distribution of the powder. As the current intensity increased, the particle size distribution of the powder became narrower, which was concentrated at 45~105 μm. In addition, the current intensity had a significant effect on the sphericity degree of the powder with the particle size > 105 μm, but it had little effect on that <105 μm powder. TiAl pre-alloyed powder with a particle size > 45 μm demonstrated a dendritic + cellular structure, and the <45 μm powder had a microcrystalline structure. The powder was mainly composed of the α2 phase and γ phase. There were two kinds of phase structure inside the powder, namely the α2 + γ lamellar microstructure (particle size < 45 µm) and the α2 + γ network microstructure (particle size > 45 µm). The phase structure of the powder was related to the solidification path and cooling rate of molten droplets in the PREP. The average thickness of the α2 + γ lamellar was about 200 nm, in which the lamellar γ phases were arranged in an orderly manner in the α2 phase matrix with a thickness of about 20 nm. The network phase structure was corrugated, and the morphology of the γ phase was not obvious.

Raman spectroscopy assisted by other analytical techniques to identify the most deteriorated carbonate‐stones to be consolidated in two monuments of Vitoria‐Gasteiz (Spain)

AbstractThis work describes the diagnostic study on the building materials, mostly carbonated, belonging to Santa Maria Cathedral and the Medieval Wall of Vitoria‐Gasteiz (Spain) with the aim to design the best conservation procedure. Both the studies of the lithology and the secondary compounds originated by environmental impacts on the Cathedral and on the Medieval Wall were carried out using laboratory instruments (μ‐Raman and micro‐energy‐dispersive X‐ray spectroscopy, X‐ray diffraction and ion chromatography) on selected samples provided by the restorers. The systematic presence of black crusts in the stones of the Cathedral was related to the growth of microcrystalline structures of secondary compounds and biological patinas and the deposition of atmospheric particles from traffic and house heating systems. In fact, the main components identified were carbon, and iron compounds such as hematite, goethite, magnetite and lepidocrocite. In addition, the detection of lead compounds (lead‐rich hydroxyapatite) suggested in the same way the impact of the urban environment on the degradation and blackening of stone materials. The presence of sulfates, mainly gypsum, and, to a lesser extent, epsomite, anhydrite and bloedite could be caused by the sulfation of carbonated compounds as a result of an acid attack of atmospheric pollutants. The results on the secondary products of the Medieval Wall showed a greater presence of degradation by microorganisms compared to the Cathedral. This is probably related to the large garden surrounding the fortification, where the grass is in direct contact to the lower part of the structure. Markers of biological activity, such as carotenoid pigments and calcium oxalate weddellite, together with other soluble oxalates were identified. The presence of ammonium nitrate, characterised by means ion chromatography, causes a chemical degradation of carbonate stone materials over time, due to the acidic nature of the ammonium ion. In both cases considered in this study, the presence of nitrate compounds, nitratine and potassium nitrate, was attributed to both natural factors (ammonium nitrate is coming from the decomposition of plant and animal excretions), and anthropogenic contamination.

Enhancement of thermal conductivity and abrasion resistance of woody carbon fiber composites via boride catalysis

In order to investigate the effect of boron element on liquefied wood carbon fibers and their composites, boric acid and boron carbide were utilized to modify liquefied wood resin through copolymerization and blending methods respectively. Then boric acid-modified liquefied wood carbon fiber (BA-WCF) and boron carbide-modified liquefied wood carbon fiber (BC-WCF) were produced via melt spinning, curing, and carbonization treatments. As expected, this modification approach effectively prevents the formation of skin-core structures and accelerates the evolution of a graphite microcrystalline structure, thereby enhancing the mechanical properties of the carbon fibers. Particularly, the tensile strength and elongation at break of BA-WCF increased to 331.57 MPa and 7.57 % respectively, representing increments of 117 % and 86 % compared to the conventional fibers. Furthermore, the as-fabricated carbon fiber/resin composites (CFPRs), composing of BA-WCF or BC-WCF as fillers and liquefied wood resin as matrix, exhibited excellent interlaminar shear strength, outstanding abrasion resistance, and well thermal conductivity, as well as electrical performance, significantly outperforming the conventional carbon fiber/phenolic resin composites. The friction rate of BC-WP/BA-WCF/CF was 2.37 %, while its thermal conductivity could reach 1.927 W/(m·K). These promising attributes lay the groundwork for the development of high-performance carbon fiber-based materials, fostering their widespread utilization across various industries.

Ultrasonic-assisted pulse electrodeposition process for producing nanocrystalline nickel films and their corrosion behavior: Competition between mass transport and nucleation

Ultrasonic-assisted pulse electrodeposition of nanocrystalline nickel (NC-Ni) coatings from Watts bath on copper substrate was investigated. Direct (DC), pulsed (PC), and pulse reversed (PRC) current electrodeposition techniques were employed to electrodeposit NC-Ni coatings in the absence and presence of ultrasound wave with a nominal power ranging from 95 W to 200 W and their surface morphology, hardness, and crystalline microstructure were compared. We observed that as the ultrasound power increases, the cathodic efficiency and the microhardness increase, whereas the crystallite size and surface roughness decrease for NC-Ni electrodeposited by the three techniques in the same way. However, the effect of pulse waveform is dominant. The finest crystallite size (24 nm) and highest hardness (585 HV) were achieved for NC Ni coatings PC electrodeposited using an ultrasound with 200 W nominal power. It is believed that the coating produced by PC and PRC techniques develops a preferential orientation in (111) and (100) planes, respectively. The application of ultrasound wave and increasing its nominal power changes the preferential orientation of all obtained coatings to (111) planes. The corrosion behavior of NC Ni coatings, as investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in NaOH solution, demonstrates the effect of nanocrystalline on the passivation and corrosion resistance of NC-Ni coatings.

Emerging continuous SiC fibers for high-temperature applications

Silicon carbide (SiC) fibers are responsible for the ultimate strength and toughness of SiC-fiber reinforced composites in harsh environments. The development of a new generation of continuous SiC fibers continues to advance the mechanical properties of composite materials. Tyranno™ SA4 fiber was recently released as a successor of Tyranno™ SA3 fiber. Laser-driven chemical vapor deposition (LCVD) has been adopted as an alternative fiber processing route to synthesizing high-strength SiC fiber with tailorable small diameters and chemical compositions. Both Tyranno™ SA4 and laser-driven CVD fibers show very high tensile strength, about 4 GPa in the as-fabricated condition. The degradation of thermal stability and strength due to annealing in an inert environment were similar for Tyranno™ SA3 and SA4 fibers because of their similar carbon-rich, crystalline microstructure. Silicon-rich fibers produced by LCVD possessed heterogeneous crystallinity, which was attributed to laser power distribution and showed microstructural instability at 1500 °C and above. The new SiC fibers demonstrated an increase in as-fabricated strength but faced the same challenges in environmental resistance as the traditional SiC fibers do.

Overview of coals as carbon anode materials for sodium-ion batteries

Abstract Energy storage is an important technology in achieving carbon-neutrality goals. Compared with lithium-ion batteries, the raw materials of sodium-ion batteries are abundant, low-cost, and highly safe. Furthermore, their costs are expected to be further reduced as large-scale applications take off, making them viable for energy storage applications. The primary anode material for sodium-ion batteries is hard carbon, which has a high sodium-ion storage capacity but is relatively expensive, limiting its applications in energy storage. In order to widen the applications of sodium-ion batteries in energy storage and other fields, it is particularly important to develop anode materials that have both high performance and low cost. Coals, with abundant reserves and worldwide availability, can serve as low-cost carbon sources for anode materials. Additionally, coals of different grades of metamorphism have different structural characteristics that can be tailored for the structural characteristics of coal-based anode materials for sodium-ion batteries. Recent research on tailoring coals as the anode materials for sodium-ion batteries is summarized and the recent progress made towards mitigating the existing issues is analysed in this review. Specifically, the impacts of different grades of metamorphism on the sodium-ion storage performance of coal-based anode materials prepared using direct carbonization are discussed in detail. Studies on improving the electrochemical performances of coal-based anode materials through pore and microcrystalline structure controls and surface as well as interface modifications are presented. Finally, the advantages and disadvantages of different preparation methods are identified. To make the industrial applications of coal-based anode materials for sodium-ion batteries more viable, the importance of the de-ashing process is introduced.

Graphitization transformation of aluminum electrolytic spent carbon cathode

Aluminum electrolysis spent cathode carbon (SCC), as typical solid hazardous waste, poses significant environmental risks. Harmless treatment of SCC and recycling of its carbon component are important research areas. In this study, SCC was subjected to microwave hydrothermal acid leaching to remove harmful components, followed by the production of high-quality graphite via iron-catalyzed graphitization. The effects of reaction temperature, heating time, and catalyst loading on the graphitization conversion of SCC were investigated. The catalytic graphitization process of SCC was optimized using the response surface method. The results show that when the reaction temperature is 1520 °C, the heating time is 85.24 min, and the catalyst loading is 46.15 wt%, the graphitization degree of the sample is 97.61 %. The samples prepared under the optimal conditions were characterized using XRD, Raman, SEM, and TEM. The results reveal that the catalytic graphitization process significantly influences the conversion of microcrystalline structures in SCC into graphite structures. The iron-catalyzed transformation of microcrystalline carbon was analyzed to elucidate the graphitization transformation mechanism. This study offers an effective pathway for the high-value utilization of SCC. It also serves as a technical reference for the catalytic graphitization conversion of carbon materials.

Effects of activated fuel and staged secondary air distributions on purification, combustion and NOx emission characteristics of pulverized coal with purification-combustion technology

Under the strategic objectives of carbon peaking and carbon neutrality, clean and efficient coal combustion was important in China. As a novel combustion technology, purification-combustion technology had good research prospects, and high-temperature reduction unit (HTRU) played a crucial role in fuel activation, subsequent combustion and NOx emissions based on the design of this technology. Despite previous research had proved the pivotal role of fuel and combustion air distributions in combustor in influencing the entire thermochemical process, there was the lack of research on their effects in HTRU employing purification-combustion technology. To realize deep NOx emission reduction, this study focused on influences of activated fuel and staged secondary air distributions in HTRU on purification, combustion and NOx emission characteristics in a 30 kW purification-combustion test rig. With the exception of carbon microcrystalline structure, the majority of reductive char properties exhibited superior performance when activated fuel was introduced tangentially, as opposed to axially. Nevertheless, the relationship of carbon microcrystalline structure was regulated by staged secondary air ratio (c12). Properly increasing c12 improved reductive char properties. Additionally, axial introduction of activated fuel more consistently yielded ultra-low levels of NOx emissions; however, this often occurred at the expense of combustion efficiency (η). Properly increasing c12 reduced NOx emissions while increasing η; nevertheless, the benefits derived from c12 were limited. By adjusting introduction direction and c12 (axial, 0.33), minimum NOx emissions decreased to 39.10 mg/m3 (@6 % O2) while maintaining high η of 99.39 %.

Study on the Evolution of Physicochemical Properties of Carbon Black at Different Regeneration Stages of Diesel Particulate Filters Regenerated by Non-Thermal Plasma

As a new type of aftertreatment technology, non-thermal plasma (NTP) can effectively decompose the particulate matter (PM) deposited in diesel particulate filters (DPFs). In this paper, a regeneration test of a DPF loaded with carbon black was carried out using an NTP injection system, and the changes of oxidative activity, elemental content, and occurrence state, microstructure and graphitization degree of carbon black were analyzed to reveal the evolution of the physicochemical properties of carbon black at different regeneration stages of the DPF regenerated by NTP. As the regeneration stage of the DPF advanced, Ti, Tmax, and Te of the carbon black at the bottom of the DPF decreased, which were higher than those at the regeneration interface. After the NTP reaction, the proportion of C element decreased to less than 80%, while the proportion of O element increased to more than 20%; C-O was converted to C=O and the relative content of C=O increased. The average microcrystalline length and average spacing decreased, while the average microcrystalline curvature increased. The ID1/IG (relative peak intensities) of carbon black samples decreased from 3.31 to 3.10, and the R3 (relative peak intensities, R3 = ID3/(IG + ID2 + ID3)) increased from 0.41 to 0.58. The content of carbon clusters had a great influence on the disorder of the microcrystalline structure, so the graphitization degree of carbon black decreased and the oxidation activity increased.

Novel titanium-based sulfur-containing BMG for PBF-LB/M

This paper investigates the additive manufacturing route for a novel glass-forming titanium-based sulfur-containing alloy of the composition Ti60Zr15Cu17S8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Ti}}_{60} {\ ext{Zr}}_{15} {\ ext{Cu}}_{17} {\ ext{S}}_{8}$$\\end{document}. This system is a promising candidate for medical devices since the lack of toxic components is combined with a high corrosion resistance and strength. Preliminary experiments and simulations show a general processability of bulk material by powder bed fusion technologies. TEM and XRD reveal an amorphous microstructure of laser-treated surfaces. Ultrasonic atomization is used to fabricate a flowable powder feed stock with spherical morphology and crystalline microstructure, which is suitable for processing in powder bed fusion. Correlations between detected crystalline phase formations and melt pool dynamics are revealed by SEM and EDX. It is shown that bulk samples with a high relative density and partially crystalline microstructure can be manufactured.

Preparation and characterization of Pr1-xNdxBaFe2O5+δ nanofiber cathodes for solid oxide fuel cells

Double perovskite oxide Pr1-xNdxBaFe2O5+δ (PNBFx, x = 0.0–0.3) nanofiber were prepared using electrospinning and were evaluated as cathodes for solid oxide fuel cells (SOFCs). The crystalline structure, microstructure, and electrochemical performance of PNBFx were thoroughly investigated and discussed. The PNBFx nanofiber cathodes obtained after sintering at 800 °C crystallized in a tetragonal structure with the space group P4/mmm and had good chemical compatibility with SDC electrolytes at 900 °C for 4 h. Nd doping was found to increase the lattice parameter, while the average valence of praseodymium and iron content increased steadily in PNBFx. The Pr0.8Nd0.2BaFe2O5+δ (PNBF02) nanofiber cathode exhibited the best performance with a polarization resistance (Rp) of 0.072 Ω cm2 at 750 °C. When PNBF02 nanofiber was used as a single-cell cathode, the peak power density reached 1.52 W cm2 at 750 °C. All results indicate that double perovskite PNBF02 is a promising cathode material for SOFCs.

Controlling the graphite-like microcrystalline structure of lignin-based ultrafine carbon fibers via the design of condensed structures

Obtaining lignin-based graphite-like microcrystallites at a relatively low carbonization temperature is still very challenging. In this work, we report a new method based on condensed structures, for regulating graphite-like microcrystalline structures via the incorporation of 4,4′-diphenylmethane diisocyanate (MDI) into the main structure of lignin. The effects of MDI on the thermal properties of lignin and the graphite-like microcrystalline structure of lignin-based ultrafine carbon fibers were extensively studied and investigated. The incorporation of MDI decreased the thermal stability of lignin, increased the carbon yield and enhanced the formation of graphite-like microcrystallites, which are beneficial for reducing energy consumption during the preparation of lignin-based carbon fibers. The modified lignin-based ultrafine carbon fibers (M-LCFs) demonstrated satisfactory electrochemical performance, including high specific capacitance, low charge transfer resistance, and good cycle performance. The M-LCFs-3/2 electrode had a specific capacitance of 241.3 F g−1 at a current density of 0.5 A g−1, and a residual ratio of 90.2 % after 2000 charge and discharge cycles. This study provides a new approach to control the graphite-like microcrystalline structure and electrochemical performance while also optimizing the temperature.

Novel ultra-low NOx coal combustion technologies based on local microenvironment targeted regulation. Part 1. Selective oxygenation

Developing a novel high-efficiency coal combustion technology with ultra-low NOx emission is urgently needed to sustain the good ecological environment. Here, the targeted regulation of local microenvironment around fuel-N, such as functional groups, radicals, molecular configurations, and reaction atmosphere, is realized by the selective oxidation. The molecular configurations, including pore networks and microcrystalline structure in coal, are well characterized through synchrotron radiation-induced SAXS (small angle X-ray scattering) and WAXS (wide angle X-ray scattering) simultaneously. Furthermore, by combining density functional theory (DFT) and experiments, the effects of the local microenvironment on the nitrogen transformation and NO evolution during the thermal conversion are focused on. The results indicate that for the PPA oxidation, the H radicals attack the adjacent carbon to pyrrole/pyridine nitrogen, promoting the conversion of fuel-N to HCN. On the other hand, for the H2O2 oxidation, disrupting the π bond electron cloud by the CO and C = O on the ortho carbon of pyrrole/pyridine dominates the NH3 generation. Additionally, the increased La (average graphene layer extent), a3 (average interlayer spacing), σ3 (standard deviation of interlayer spacing) and σ1 (standard deviation of the first-neighbor distribution) induce massive smaller pores, promoting the generation of abundant reaction defects inside the particles. Importantly, the intensified adsorption on abundant active sites lead to the decreased HCN and increased NH3 evolution, which is adverse for the interaction between homogeneous and heterogeneous NO reduction. Interestingly, the PAA selective oxidation can reduce NO emission by 31.72 % - 34.30 % during the air combustion, which is far better than the H2O2 oxidation. Overall, the attack of free radicals on nitrogen-containing heterocycles promotes the conversion of fuel-N to HCN, the adsorption of which on char surfaces can further enhance the heterogeneous reduction in a lean oxygen atmosphere. The work here provides a novel route for developing high-efficiency and low-NOx combustion technologies.

Vat photopolymerization of biomimetic bone scaffolds based on Mg, Sr, Zn-substituted hydroxyapatite: Effect of sintering temperature

In response to the urgent demand for innovative bone regeneration solutions, the focus of this study is to develop and characterize Mg, Sr, Zn-substituted calcium phosphate scaffolds that replicate the trabecular architecture of cancellous bone. Ion substitution represents a promising approach to improve the biological effectiveness of calcium phosphates and composite materials used in bone tissue engineering applications. Porous scaffolds mimicking the natural bone structure were additively manufactured from the photosensitive ceramic suspensions for vat photopolymerization using digital light processing. The impact of the selected trace elements (0, 1 and 5 mol.% substitution) and the sintering temperature (900, 1000, 1100, 1200, and 1300 °C) was investigated in relation to the obtained crystalline phase content, microstructure, elemental distribution, thermal stability, and mechanical properties. After sintering, in addition to hydroxyapatite, β-tricalcium phosphate was detected as a result of the added trace elements in the calcium-deficient hydroxyapatite used as a starting powder. The obtained scaffolds exhibited uniform distribution of the trace elements, and they feature 3D-designed porosity predominantly ranged from 10 to 900 μm in diameter, with an average pore size of 546.25 ± 10.95 μm. The total porosity of scaffolds was 76.24 ± 1.32 vol% and an average wall thickness of 217.03 ± 8.98 μm, closely resembling the morphology of cancellous bone tissue. The mechanical properties of the scaffolds sintered at 1100 °C, 1200 °C, and 1300 °C were in line with those typically observed in trabecular bone. The study demonstrates the feasibility of using custom made bioactive hydroxyapatite powders together with vat photopolymerization to design the porosity and properties of the bone scaffolds on demand, based on the requirements of individual bone defects.

Additively manufactured low-gradient interfacial heterostructured medium-entropy alloy multilayers with superior strength and ductility synergy

Metallic additive manufacturing (AM) offers near net-shape fabrication but often results in insufficient strength and/or ductility due to voids or cracks, coarse initial crystalline microstructure, insufficient volume fraction of precipitates and yet post-AM strengthening/toughening methods non-destructive to shape are generally lacking. Here, we report a laser-directed energy deposited (L-DED) medium entropy alloy (MEA) with a heterostructure (HS) comprising alternate layers of solid-solution and intermetallic-dispersed MEA that possess ultimate tensile strength of 1132.8 MPa and elongation of 50.6 %, corresponding to strength-ductility synergy higher than other medium- or high-entropy alloys reported. The multilayers were produced from a dual source of CoCrNi MEA powder and a powder mixture of the same MEA, Al and Ti with stoichiometry (CoCrNi)86Al7Ti7, and the remarkable strength-ductility synergy is achieved only after post-L-DED heat treatment, which causes Al and Ti to diffuse across the layers to form a low-gradient HS. The significant back stress due to the HS contributes to the high strength, while the high ductility results from a high strain-hardening rate suppressing necking. This study demonstrates the concept of using AM not just as a near net-shape fabrication method but also a unique tool to produce low-gradient HSs with superb mechanical properties, via the use of multiple powder sources combined with suitable shape-preserving post-fabrication heat treatment.

Sintering behaviors, microstructure and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The aim of this work was to investigate the impacts of MgO on the crystalline behaviors, microstructure, and properties of CaO–B2O3–SiO2 (CBS) glass-ceramics. In the study, the CBS samples with various MgO contents were developed via the melting and quenching route. Subsequently, a CBS casting tape and a multi-layered LTCC microcircuit module were created by using the tape casting method. Results indicated that MgO could break the glass network and promote the formation of liquid phase during the sintering process. A suitable amount of MgO additive promoted densification during firing process and improved the properties of the CBS materials. The CBS sample with 1.5 wt% MgO fired at 875 °C exhibited outstanding properties, including a dielectric constant (εr) of 6.5 (at 10 GHz), a dielectric loss (tan δ) of 8 × 10−4, a flexural strength of 167 MPa, a coefficient of thermal expansion (CTE) of 6.8 ppm/°C, and a thermal conductivity (λ) of 2.2 W/mK. In addition, this LTCC material demonstrated good co-firing compatibility with silver electrodes and superior temperature stability, showing its great potential for microelectronic applications.