Subsequent Sintering Research Articles

Sequential activation of M1\xa0and M2 phenotypes in macrophages by Mg degradation from Ti-Mg alloy for enhanced osteogenesis

BackgroundEven though the modulatory effects of Magnisum (Mg) and its alloys on bone-healing cells have been widely investigated during the last two decades, relatively limited attention has been paid on their inflammation-modulatory properties. Understanding the activation process of macrophages in response to the dynamic degradation process of Mg as well as the relationship between macrophage phenotypes and their osteogenic potential is critical for the design and development of advanced Mg-based or Mg-incorporated biomaterials.MethodsIn this work, a Ti-0.625 Mg (wt.%) alloy fabricated by mechanical alloying (MA) and subsequent spark plasma sintering (SPS) was employed as a material model to explore the inflammatory response and osteogenic performance in vitro and in vivo by taking pure Ti as the control. The data analysis was performed following Student’s t-test.ResultsThe results revealed that the macrophages grown on the Ti-0.625 Mg alloy underwent sequential activation of M1 and M2 phenotypes during a culture period of 5 days. The initially increased environmental pH (~ 8.03) was responsible for the activation of M1 macrophages, while accumulated Mg2+ within cells contributed to the lateral M2 phenotype activation. Both M1 and M2 macrophages promoted osteoblast-like SaOS-2 cell maturation. In vivo experiment further showed the better anti-inflammatory response, regenerative potentiality and thinner fibrous tissue layer for the Ti-0.625 Mg alloy than pure Ti.ConclusionThe results highlighted the roles of Mg degradation in the Ti-0.625 Mg alloy on the sequential activation of macrophage phenotypes and the importance of modulating M1-to-M2 transition in macrophage phenotypes for the design and development of inflammation-modulatory biomaterials.

Ag metal interconnect wires formed by pseudoplastic nanoparticles fluid imprinting lithography with microwave assistant sintering

Nanoimprint technology has the advantages of low cost, high precision, high fidelity and high yield. The metal nanoparticle fluid is non-Newtonian fluid, which is used as the imprint transfer medium to realize high fidelity of pattern because of its shear thinning effect. In order to functionalize the metal nanoparticles microstructure, the subsequent sintering step is required to form a metal interconnect wire. Metal interconnect wire with fewer grain boundaries and fewer holes have excellent mechanical and electronic properties. In this paper, the pseudoplastic metal nanoparticle fluid was formed by Ag nanoparticle and precursor solution, and then the thermal diffusion process was completed by microwave sintering after interconnects were embossed. The influence of microwave and thermal atmosphere on the microstructure and performance of Ag Interconnect wires was analyzed and discussed, and the Ag Interconnect wires performance was determined under the influence of time and temperature parameters. In our experiments, the interconnects after microwave sintering can achieve 39% of the conductivity of bulk silver. The microwave sintering module might be integrated as the heat treatment module of the metal micro/nano pattern directly imprint lithography.

Aluminum alloys with high elastic modulus

Binary Al-5M alloys, containing 5 at.% alloying element (M: Cr, Si, Nb, Mo, and V), have been produced by high-energy ball milling and subsequent spark plasma sintering. X-ray diffraction analysis indicated the solid solubility of the alloying elements to be several orders of magnitude higher than that predicted by the phase diagram. The elastic modulus and hardness of Al-5M alloys, analyzed using nanoindentation, were significantly higher than the commercial Al alloys. High elastic modulus was attributed to the decrease in lattice parameters as a result of the extended solid solubility of the alloying elements.

Impact of Preparation Method and Y2O3 Content on the Properties of the YSZ Electrolyte

This study is an effort to cover and interconnect multiple aspects of the fabrication of the yttria-stabilized zirconia (YSZ) from powder preparation to a solid electrolyte suitable for utilization in solid oxide cells. Thus, a series of YSZ electrolytes was prepared, differing in the content of the Y2O3 dopant and in the method of preparation. Combustion synthesis along with the thermal decomposition of precursors was used for YSZ powder synthesis with a dopant content of 8 to 18 mol.%. Post-synthesis treatment of the powder was necessary for achieving satisfactory quality of the subsequent sintering step. The morphology analyses of the YSZ powders and sintered electrolytes produced proved that small particles with a uniform size distribution are essential for obtaining a dense electrolyte. Furthermore, the conductivity of YSZ electrolytes with different Y2O3 contents was examined in the temperature range of 400 to 800 °C. The lowest conductivity was found for the sample with the highest Y2O3 content. The obtained results enable the preparation methods, YSZ powder morphology, and composition to be connected to the mechanical and electrochemical properties of the YSZ electrolyte. Thus, this study links every step of YSZ electrolyte fabrication, which has not been sufficiently clearly described until now.

Wet ball milling and subsequent high-speed selective laser sintering of Nb[sbnd]Cu powders for applying wear-resistant coatings

The work investigates niobium-carbohydride- and copper-based powders prepared via wet ball milling of niobium and copper in petroleum ether, including their phase composition evolution under heat treatment. High-speed selective laser sintering of the prepared powders on iron substrates provides gradient coatings ~70 μm thick. The outer layer of the coating contains phases of NbC0.75, Nb2C, (Fe,Nb)6C, Cu, and Fe, whereas the 10-μm layer adjacent the substrate shows the presence of NbC0.75, (Fe,Nb)6C, Fe2Nb, Сu, and Fe. Dry friction with a WC–Co counterbody does not cause wear of the coatings, and the friction coefficient being ~0.6. High wear resistance of the coatings results from their structure including regions containing nanosized niobium carbides (50–500 nm) with a hardness of ~11 GPa, regions of Fe + Fe2Nb eutectic reinforced with niobium carbide inclusions with a hardness of 6.5 GPa, and copper inclusions working as a solid lubricant in tribological tests.

Effect of mechanical milling and sintering on magnetic entropy of Ni-based Ni2CuCrFeAl x (x = 0.5, 1.0, 1.5 and 2.5) high entropy alloys

ABSTRACT Nickel-based Ni2CuCrFeAl x (x = 0.5, 1.0, 1.5 and 2.5) high-entropy alloys with good magneto-caloric properties have been successfully prepared by a mechanical milling technique. The phase transformation from FM to PM at the transition point was linear with composition and T c, respectively. Substitution of Al by mechanical milling with subsequent sintering induces a tetragonal distortion in the BCC structure. Prolonged hours of milling followed by sintering result in an increase in magnetic entropy that may result in high refrigeration capacity (RC). Temperature-dependent isothermal magnetization exhibits second-order magnetic phase transition with varying temperature. Moreover, it could be envisaged that distortion occurs in the alloy not only due to the milling effect, but sintering also plays a vital role in achieving large magnetic entropy due to the formation of different intermetallics. This study shows the variation in magnetic entropy of the alloy prepared by mechanical milling followed by sintering at 1073 K.

Transparent AlON ceramics by nitriding combustion synthesis precursors and pressureless sintering method

Fine AION powders (D50 = 607 nm) with high sintering activities were synthesized by a high-efficiency solution combustion-based method, and a high-transmittance AlON ceramics can be achieved by a subsequent sintering process. Moreover, the influences of various aluminum resources (Al(NO3)3, AlCl3 and Al2(SO4)3) on the morphology of precursors and nitride-functionalized products have been studied in detail. Using Al(NO3)3 as aluminum source resulted in more active precursors and was beneficial for the preparation of ultrafine AlON powders. Then, single-phase AlON powders were obtained by calcining precursors at 1700 °C for 10 min, while residual Al2O3 was observed in the calcined products synthesized by other two aluminum sources. As a result, transparent AlON ceramics with high in-line transmittance of 85.9% at 2 μm were obtained. This research provides valuable reference for rapid preparation of AlON powders and transparent ceramics.

First-principles prediction, fabrication and characterization of (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 high-entropy borides

The microstructure and mechanical properties of (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 high-entropy boride (HEB) were first predicted by first-principles calculations combined with virtual crystal approximation (VCA). The results verified the suitability of VCA scheme in HEB studying. Besides, single-phase (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 ceramics were successfully fabricated using boro/carbothermal reduction (BCTR) method and subsequent spark plasma sintering (SPS); furthermore, the effects of different amounts of B4C on microstructure and mechanical properties were evaluated. Due to the addition of B4C and C, all samples formed single-phase solid solutions after SPS. When the excess amount of B4C increased to 5 wt%, the sample with fine grains exhibited superior comprehensive properties with the hardness of 18.1 ± 1.0 GPa, flexural strength of 376 ± 25 MPa, and fracture toughness of 4.70 ± 0.27 MPa m1/2. Nonetheless, 10 wt% excess of B4C coarsened the grains and decreased the strength of the ceramic. Moreover, the nanohardness (34.5–36.9 GPa) and Young's modulus (519–571 GPa) values with different B4C contents just showed a slight difference and were within ranges commonly observed in high-entropy diboride ceramics.

Inductive proximity sensors within a ceramic package manufactured by material extrusion of binder-coated zirconia

The embedding of electric components into additively manufactured structures offers enormous potential for extending the functionality and applications of parts produced by additive manufacturing (AM). However, the production of electric components embedded with 3D-printed ceramic structures has been a significant challenge due to the complexity of the manufacturing process and the high-temperature post-processing it requires. In the present study, an inductive proximity sensor with a 3D-printed ceramic housing and embedded sensing elements was designed and produced using a hybrid manufacturing process in which the printing process is paused and a sensing element is embedded into the printed structure. Sensing elements materials were carefully selected and intra-sensor structures were developed to ensure that the sensing element would survive in a high-temperature sintering environment. In the developed process, binder-coated zirconia containing 87 wt% was used as feedstock in a piston-based material extrusion process to fabricate the ceramic housing for the sensor, and platinum wire was used in the sensing element. The subsequent debinding and sintering processes achieved a nearly fully dense ceramic housing that protects the sensor in harsh environments. The successfully fabricated sensor was tested by measuring the change of distance between the inductive and metallic target and determining if the changes in distance would alter the inductance of the sensor. Results show that the sensing element maintains functionality throughout each fabrication step, and the fully packaged sensor also demonstrates the ability to work properly at high temperatures (in the range of 200–400 °C). At a frequency of 2 MHZ and a voltage of 1 V, the inductive sensor has a measurement range of approximately 7.0 mm. Additive manufacturing of the sensor housing enabled precise control of the geometry, dimensions, and infill density. Because the developed methodology allows for control of the type and structure of the sensing element, it can be used in the manufacture of a wide variety of sensors or smart components.

Effect of Bi2O3 contents on magnetic and electromagnetic properties of LiZnMn ferrite ceramics

Soft LiZnMn ferrites with low coercive force values and small grain sizes were developed by the solution combustion synthesis and low temperature sintering technique for microwave applications at a high frequencies. Bismuth oxide was used as an additive to lower the sintering temperature. The examination covered the influence of Bi2O3 on the crystal structure, microstructure, primary magnetic and dielectric characteristics of lithium-zinc-manganese ferrites. The most promising sample designed for using in microwave devices was produced by sintering at 1075 ℃ temperature for 8 h with added 1.5 wt% Bi2O3. These production conditions have yielded 2.98 µm average grain size in a ceramic product, the density is 4.84 cu cm/g, and the coercive force, residual induction, and saturation induction are 58 A/m, 2078.4 G, and 3439.1 G, respectively. In addition, this sample demonstrates a high initial magnetic permeability (μi = 168), Curie temperature (Tc = 437.5 ℃), high values of the dielectric loss tangent (tan δɛ = 6.32⸱10−3), ferromagnetic resonance line width (ΔH = 280 Oe) and the resonance line of spin waves (ΔHk = 1.87 Oe). Further increase in the bismuth oxide content allows observing a change in the ceramics microstructure, accompanied by a deterioration in the magnetic and electromagnetic characteristics. Here, the discussion covers the mechanism of change in the functional properties of lithium-zinc-manganese ferrites produced in the conditions of solution combustion with added bismuth oxide. Thus, synthesizing of initial pre-ceramic powder by glycine-nitrate combustion and subsequent low-temperature sintering with added bismuth oxide is a novel efficient technique of producing advanced soft high-frequency LiZnMn ferrites.

Industrial Silicon-Wafer-Wastage-Derived Carbon-Enfolded Si/Si-C/C Nanocomposite Anode Material through Plasma-Assisted Discharge Process for Rechargeable Li-Ion Storage.

Silicon is a promising anode material for high-performance Li-ion batteries as a result of its high theoretical specific capacity and elemental abundance. Currently, the commercial application of the Si-based anode is still restricted by its large volume changes during the lithiation cycles and low electrical conductivity. To address these issues, we demonstrate a facile plasma-assisted discharge process to anchor nano-sized Si particles into methanol with quick quenching. After the subsequent sintering process, we obtained a Si/SiC/C composite (M-Si). The unique structure not only allowed for the electrolyte infiltration to enhance lithium ion diffusion during charge and discharge process, but also buffered the volume expansion of silicon particles to enhance the rate capability and cycle stability. The M-Si cell electrochemical results exposed good Li-ion storage performance compared to that of the bare Si used cell (B-Si). The electrode cell consisting of M-Si exhibited remarkable enhanced cyclic stability and sustained the reversible specific capacity of 563 mAhg−1 after 100 cycles, with a coulombic efficiency of 99% at a current density of 0.1C, which is higher than that of the B-Si electrode cell that was used. Hence, the as-prepared Si/SiC/C composite is an efficient anode material for Li-ion battery applications. Moreover, these results indicate that the novel plasma-assisted discharge technique will bring a potential durable methodology to produce novel high-performance electrode materials for future advanced large-scale energy-storage applications.

A Study of Compaction Densification Behavior of Composite Particles by Multiparticle Finite Element Method

In this paper, 3D particulate scale modelling on the die compaction of DEM generated initial packings of both soft and hard particles was conducted by employing the multiparticle finite element method (MPFEM). The effects of initial packing structures as well as the compaction pressure on the macroscopic and microscopic properties of the whole powder mass and local structures were investigated. In addition, corresponding physical experiments were carried out for model validation. The results show that the compact obtained from the initial dense packing under vibration undergoes yielding stage earlier than that with natural initial packing (without vibration), and the relative density is much higher. Pores that are significantly smaller and with more uniform size and homogenous stress distribution are observed in the former case. Highest stress regions occur in most cases at a grain boundary with large curvature after deformation. Moreover, the high stress in the central part of both soft and hard particles during compaction is significantly reduced after pressure unloading, reaching a new force balance. In this case, the stress is concentrated mainly at the corners of the deformed particles, which creates the risk of cracking during subsequent sintering at either the contact region between particles or the corners. The numerical results are found to be in good agreement with those from physical experiments, confirming the robustness and reliability of the numerical model used in the simulations.

Effect of binder jetting microstructure variability on low cycle fatigue behavior of 316L

Despite the growing interest for Binder Jet Additive Manufacturing (BJAM), variability in the mechanical properties hinders its industry wide adoption. In order to reduce the variability, the underlying failure mechanisms should be understood. In the present work, a stainless steel 316 L alloy powder is used to generate BJAM parts with different microstructures via changing the powder particle size distribution and post-processing heat treatment. The effects of the microstructural features such as porosity, grain size, secondary phases and annealing twins on fatigue failure mechanisms are analyzed. The results show that the primitive porosity lines generated during BJAM process are the major cause of fatigue crack initiation and mechanical variability. These lines led to the formation of elongated pores during subsequent sintering, causing a reduction in the fatigue life and an increase in the data scattering. It is shown that a minimum level of green density prior to sintering is necessary to reduce the occurrence of this networked porosity. Moreover, the use of HIP treatment removed the process induced porosity and reduced scattering of the fatigue life but did not impact the average fatigue life significantly. The benefit of porosity reduction and pore roundness after HIP treatment appears to be greatly offset by grain coarsening and formation of annealing twins during HIP.

Enhanced Thermoelectric Properties of Cu2SnSe3-Based Materials with Ag2Se Addition.

In this work, (Ag, In)-co-doped Cu2SnSe3-based compounds are prepared using a self-propagating high-temperature synthesis process. Ag2Se and as-synthesized (Ag, In)-co-doped Cu2SnSe3-based powders are mixed in a proportion according to the formula of Cu1.85Ag0.15Sn0.91In0.09Se3/x Ag2Se (x = 0, 3, 4, and 5%), which is followed by a subsequent plasma-activated sintering (PAS) to obtain consolidated composite bulks. A sandwich experiment is designed to reveal the evolution of the microstructure and phase composition of the composite samples during the PAS process. We investigate the reaction mechanism between Ag2Se and Cu2SnSe3-based matrix as well as the influence of Ag2Se on the phase composition, microstructure, and thermoelectric transport properties of the composites. Ag2Se addition is proven to be effective to improve Ag solubility in the Cu1.85Ag0.15Sn0.91In0.09Se3 matrix and introduce a CuSe secondary phase and an Ag-rich phase at grain boundaries. The electrical conductivity of Cu1.85Ag0.15Sn0.91In0.09Se3/x Ag2Se (x = 0, 3, 4, and 5%) composites decreases while the Seebeck coefficient increases with increasing Ag2Se addition, resulting in an optimized power factor. Moreover, benefiting from the collective phonon scattering at various defects induced by Ag2Se addition, the composite samples exhibit significantly suppressed lattice thermal conductivity, which reaches as low as 0.11 W m-1 K-1 at 700 K for the x = 5% sample. A peak figure-of-merit (ZT) of 1.26 at 750 K and an average ZT of 0.75 at 300-800 K are obtained for Cu1.85Ag0.15Sn0.91In0.09Se3/5% Ag2Se. This work provides an efficient way to improve average ZT values of Cu2SnSe3-based compounds for promising power generation at intermediate temperatures.

The Influence of Thermal Dilution on the Microstructure Evolution of Some Combustion-Synthesized Refractory Ceramic Composites

Modeling the self-sustained high-temperature synthesis (SHS) reaction via thermal dilution and transformation of the reaction heterogeneous media into a moderate exothermic one has unlimited potential for designing inorganic powders of a certain morphology beneficial for advanced consolidation. Thermal/inert dilution of the high-exothermic mixtures leads to the fluent decrease of both the combustion temperature and velocity, thus allowing to tailor the thermal regime of the combustion process, therewith contributing to high yield of reaction and governing the microstructural features of the combustion products. In the current review, we shed on light on the possibilities of this effective strategy to control the thermal behavior of the SHS process for the preparation of applicable powder precursors for the subsequent successful sintering. Since the SHS process of some refractory ceramics (MoSi2, TiB2, TiC, etc.) involves a relatively violent reaction rate and high combustion temperature, achieving a high level of microstructure control in these systems is often challenging. The challenge was tackled with a thermal dilution approach, attaining considerable enhancement in the homogeneity among phases with an increase of diluent content along with microstructure refinement.

Development of a Material Extrusion Additive Manufacturing Process of 1.2083 steel comprising FFF Printing, Solvent and Thermal Debinding and Sintering

In recent years, Fused Filament Fabrication (FFF) of feedstock comprising metal powder and a polymer binder system attracted more and more attention as an extrusion-based Additive Manufacturing method. Allowing for the production of intricate geometries at reasonably low cost, FFF and subsequent debinding and sintering is an attractive solution for producing complex parts made of metals or ceramics. This study investigates the FFF, debinding and sintering process chain for 1.2083 (AISI 420) tool steel. The effect of printing temperature, printing speed and filament feed rate on the density of the green body was evaluated. With regard to the subsequent solvent debinding the required time for complete binder removal was determined as a function of the maximum part thickness. Based on a thermogravimetric analysis (TGA) the decomposition behavior of the remaining insoluble binder was monitored and accordingly a temperature program for the thermal debinding was derived. The sintering curve was determined by dilatometry. Finally, the capability of the process is demonstrated by manufacturing an impeller geometry and examining the resulting microstructure and hardness of the material.

Alignment of strontium hexaferrite, by cold compaction of anisotropic non-magnetically interacting crystallites.

Cold compacted, anisotropic shaped non-magnetically interacting precursors are used to achieve aligned strontium hexaferrites. The simple process of dry mixing platy hematite and/or rod-like goethite with strontium carbonate removes the need for external magnetic fields or high temperatures during compaction to assist in alignment. The calcined strontium hexaferrite pellets all displayed preferred orientation and high levels of phase purity (>99 wt%). The mix of goethite and strontium carbonate achieved the highest degree of magnetic alignment with Mr/Ms reaching 0.83(1) obtained by vibrating sample magnetometry. The magnetic data were supported by examining crystallographic alignment using powder X-ray diffraction as well as 2D texture synchrotron analysis.

B2-ordered NiAl content on microstructure, mechanical and oxidation properties of FeAl intermetallic compounds

B2-ordered FeAl based materials with 0, 10, 20, 30, 40, 50 and 60 wt.% B2-ordered NiAl reinforced phase were prepared by mechanical alloying with subsequent hot-pressing sintering. The microstructure, mechanical properties and oxidation resistance were investigated. The results showed that after adding NiAl, the main phase was composed of B2-ordered NiAl, B2-ordered FeAl phase, a small amount of AlFe3C0.5 and α-Al2O3. With the increase of NiAl content, the hardness and compressive strength of NiAl/FeAl composites first increased and then decreased. When the content of NiAl increased to 30 wt.%, the hardness and compressive strength of NiAl/FeAl composite reached the maximum value of 50.30 HRC and 2053.43 MPa, which was 35.2% and 40.8% higher than FeAl alloy. Besides, with the increase of NiAl content, the formation of dense oxide film on the surface was easier and faster, and the oxidation resistance was gradually improved. When the content of NiAl increased to 60 wt.%, the oxidation weight gain of NiAl/FeAl composite was 0.19 mg/cm2. Compared with FeAl alloy, the oxidation resistance of 60 wt.% NiAl/FeAl was increased by 81%, and the thickness of oxide layer was reduced from 1.527 μm to 0.253 μm. At this time, the oxide on the surface of the oxidized sample was mainly composed of α-Al2O3, α-Fe2O3 and a small amount of NiO.

Synergistic Strengthening of Mechanical Properties and Electromagnetic Interference Shielding Performance of Carbon Nanotubes (CNTs) Reinforced Magnesium Matrix Composites by CNTs Induced Laminated Structure.

In this study, we reported a laminated CNTs/Mg composite fabricated by spray-deposition and subsequent hot-press sintering, which realized simultaneous enhancement effects on strength and electromagnetic interference (EMI) shielding effectiveness (SE) by the introduced CNTs and CNT induced laminated ‘Mg-CNT-Mg’ structure. It was found that the CNTs/Mg composite with 0.5 wt.% CNTs not only exhibited excellent strength-toughness combination but also achieved a high EMI SE of 58 dB. The CNTs increased the strength of the composites mainly by the thermal expansion mismatch strengthening and blocking dislocation movements. As for toughness enhancement, CNTs induced laminated structure redistributes the local strain effectively and alleviates the strain localization during the deformation process. Moreover, it could also hinder the crack propagation and cause crack deflection, which resulted in an increment of the required energy for the failure of CNTs/Mg composites. Surprisingly, because of the laminated structure induced by introducing CNTs, the composite also exhibited an outperforming EMI SE in the X band (8.2–12.4 GHz). The strong interactions between the laminated ‘Mg-CNT-Mg’ structure and the incident electromagnetic waves are responsible for the increased absorption of the electromagnetic radiation. The lightweight CNTs/Mg composite with outstanding mechanical properties and simultaneously increased EMI performance could be employed as shell materials for electronic packaging components or electromagnetic absorbers.

Influence of incongruent dissolution-precipitation on 8YSZ ceramics during cold sintering process

The incongruent dissolution-precipitation behaviors of 8YSZ (8 mol% yttria-stabilized zirconia) ceramics during cold sintering process is studied in this paper by changing the pH of liquid media. The different solubility of Y3+ and Zr4+ at the same lattice position causes the disparate dissolution behaviors, and results in incongruent precipitation. Compared with acidic or alkaline solution, neutral solution is more conducive to the incongruent dissolution-precipitation process, and the concentration ratio of dissolved Y3+ and Zr4+ can reach ∼6385. The incongruent dissolution-precipitation process facilitates the formation of neck structure and promotes the ionic migration and diffusion at the subsequent high-temperature sintering process, which improves the mechanical properties and electrochemical properties of 8YSZ ceramics. This work reveals the principle of incongruent dissolution-precipitation process of zirconia-based ceramics, and it is of significance for selecting suitable liquid media to control the incongruent dissolution-precipitation behaviors in cold sintering process to prepare high-performance zirconia-based ceramics.