Starting Powder Size Research Articles

Fabrication of flat stainless steel substrates with improved oxidation behavior for metal-supported solid oxide cells using aqueous tape casting

An aqueous tape casting procedure was developed and optimized to fabricate thick, flat tapes for use as porous stainless-steel substrates for metal-supported solid oxide cells (MS-SOCs). Curling tape is one of the main challenges when using aqueous based slurry formation. This work demonstrated that the sedimentation problem can be solved by increasing solid loading rather than adding excessive binder to raise viscosity. The effect of various casting surfaces on tape curling was also investigated. Materials that allow easy tape release resulted in flatter tapes once the water was evaporated. In addition, substrate oxidation resistance at high temperature was evaluated with respect to starting powder size, sintering extent, and pore former types. High sintering extent that removes or encloses the porosity between steel particles while retaining porosity left by pore formers can effectively prevent breakaway oxidation due to local chromium depletion. Carbon residue in the steel substrates from the slurry organic content can be decreased when formulating the slurry to prevent Cr-rich phase formation in the steel, which severely compromises the substrate oxidation resistance and ductility. By dwelling the substrate in high purity hydrogen, the sensitization can be reversed, but more detailed investigation of the reaction dynamics is needed. By combining the strategies described, this work produced crack-free, flat, 400–500 μm thick stainless steel substrates with 28.7 vol% porosity and improved oxidation resistance compared to previous substrates fabricated by dry pressing of fine powders.

Effect of powder size and geometry on consolidation of Mo30%W alloy by spark plasma sintering

Molybdenum alloys are important structural components for a variety of high temperature applications in the aerospace and nuclear industries. Spark plasma sintering has been successful in producing highly dense refractory metals with desirable microstructural characteristics, where the final microstructure and sintering mechanisms depend heavily on the starting powder size and morphology. To understand how powder size and morphology affect consolidation of a molybdenum 30 wt% tungsten alloy (Mo30W), three different powder feedstocks were sintered and the solid compacts characterized. These powders were prepared utilizing chemical reduction, ball-milling, and gas atomization processes. Additionally, to determine the effect of particle size on sintering, two different size distributions of the gas atomized material were also tested. In-situ sintering dilatometry data was analyzed to determine the apparent activation energy for the initial stage sintering of each powder. Powder geometry was found to have the greatest impact on the sintering of Mo30W powders, with the rougher, more angular powders densifying at lower temperatures compared with the smoother spherical powders densifying at higher temperatures. Powder size contributed much less to the densification of the powders using SPS. From these experiments, optimum sintering temperatures can be determined, with 1600 °C being sufficiently high to fully densify the chemical reduction and ball-milled materials and a maximum hold temperature of >1800 °C being required for the spherical atomized powders.

Process and feedstock driven microstructure for laser powder bed fusion of 316L stainless steel

In the pursuit of improving additively manufactured (AM) component quality and reliability, fine-tuning critical process parameters such as laser power and scan speed is a great first step toward limiting defect formation and optimizing the microstructure. However, the synergistic effects between these process parameters, layer thickness, and feedstock attributes (e.g. powder size distribution) on part characteristics such as microstructure, density, hardness, and surface roughness are not as well-studied. In this work, we investigate 316L stainless steel density cubes built via laser powder bed fusion (L-PBF), emphasizing the significant microstructural changes that occur due to altering the volumetric energy density (VED) via laser power, scan speed, and layer thickness changes, coupled with different starting powder size distributions. This study demonstrates that there is not one ideal process set and powder size distribution for each machine. Instead, there are several combinations or feedstock/process parameter ‘recipes’ to achieve similar goals. This study also establishes that for equivalent VEDs, changing powder size can significantly alter part density, GND density, and hardness. Through proper parameter and feedstock control, part attributes such as density, grain size, texture, dislocation density, hardness, and surface roughness can be customized, thereby creating multiple high-performance regions in the AM process space.

Physical Characterization of Sintered NiMnGa Ferromagnetic Shape Memory Alloy.

The present work focused on the microstructural, thermal, electrical, and damping characterization of NiMnGa samples produced through a powder pressing and a sintering process; the effect of sintering times and of the starting powder size were evaluated. Moreover, an observation of the evolution of martensitic transformation typical of NiMnGa ferromagnetic shape memory alloy was conducted in comparison with the cast material behavior and in correlation with the material densification. The optimum powder size and sintering time for the process, i.e., 50 µm or lower and 72 h, were identified considering the investigated physical properties of the sintered samples in comparison to the cast material. The corresponding sample showed the best compromise between density, thermal and electrical properties, and damping and functional behaviour. In general, the outcomes of this study could be the basis of a useful tool for production processes that include a sintering step as well as being a starting point for the evaluation of an alternative low cost fabrication method of this alloy.

New Application Area for Nitride Based Ceramics as Optical Materials

This study is focused on the production of translucent nitride based ceramics changing different parameters such as additive, starting powder size and sintering conditions. Therefore, two different processes were followed in this research. In first one translucent SiAlON ceramics were improved by controlling specific parameters which were mentioned above. In the second stage, translucent Si3N4 ceramic was obtained also the controlling same parameters. This is a very important result for aerospace and defence industry applications due to these materials high temperature resistivity and mechanical properties.

Optimization of the optical properties of α-SiAlON through a decrease in starting powder size

In the present work, the effects of initial powder size on the sintering behavior and optical properties of Dy-α-SiAlON ceramics produced by the SPS technique are investigated. The powders were prepared using high energy and conventional milling processes to make comparisons. The powders, prepared by conventional processes, were used as a standard. After sintering, the infrared transmittance behavior of the SiAlON ceramics was investigated in a wavenumber range of between 7000 and 1000cm−1 using an FTIR. The microstructure and phase characterization of the samples were carried out using an SEM and the XRD method, respectively. It was observed that the secondary crystalline phases, the sizes of grains and the distribution of the glassy phase around the grains were the main factors that affected the transmittance of the samples. As a result, it was shown that the starting particle size of raw materials had a significant effect on the microstructure and optical properties of the samples.

Grain refining in spark plasma sintering Al2O3 ceramics

The paper reports the effect of starting powder size and sintering temperature on the grain refining in spark plasma sintering Al2O3. It was found that the grain refining effect only occurred for the starting particles larger than a certain size. The grain size increased with increasing sintering temperature. The grain refining is likely caused by the rearrangement of dislocations through a thermo-mechanical fatigue process. It suggested that nanostructured alumina ceramics could be synthesized from micro-sized powders by optimizing the particle size and sintering temperature.

Effects of starting powder and thermal treatment on the aerosol deposited BaTiO3 thin films toward less leakage currents.

To prepare high-density integrated capacitors with low leakage currents, 0.2-μm-thick BaTiO3 thin films were successfully deposited on integrated semiconductor substrates at room temperature by the aerosol deposition (AD) method. In this study, the effects of starting powder size were considered in an effort to remove macroscopic defects. A surface morphology of 25.3 nm and an interface roughness of less than 50 nm were obtained using BT-03B starting powder. The nano-crystalline thin films achieved after deposition were annealed at various temperatures to promote crystallization and densification. Moreover, the influence of rapid thermal annealing process on the surface morphology and crystal growth was evaluated. As the annealing temperature increased from room temperature to 650°C, the root mean square (RMS) roughness decreased from 25.3 to 14.3 nm. However, the surface was transformed into rough performance at 750°C, which agreed well with the surface microstructure trend. Moreover, the crystal growth also reveals the changes in surface morphology via surface energy analysis.

에어로졸 데포지션 법을 이용하여 제조한 SiO2후막의 구조 및 광학 특성

Aerosol deposition(AD) coating that enable fabricate films at low temperature have begun to be widely researched for the integration of ceramics as well to realize high-speed deposition rates. For application of ceramic thick film by AD to display and electronic ceramic industry, fabrication of dense structure with a no cracking is required. In this study, to fabricate dense ceramic thick film, the effect of crystal phase of starting powder was investigated. For this study, amorphous and crystalline <TEX>$SiO_2$</TEX> powders were used as starting powders. Two types of <TEX>$SiO_2$</TEX> powders were deposited on glass substrate by AD. In the case of amorphous <TEX>$SiO_2$</TEX> powder, the deposited films had extremely incompact and opaque layer, irrespective of particle size. In contrast to amorphous powder, in the case of crystalline powder, porous structure layer and dense microstructure with no cracking layer were fabricated depending on the particle size. The optimized starting powder size for dense coating layer was <TEX>$1{\sim}2{\mu}m$</TEX>. The transmittance of film reached a maximum of 76% at 800 nm.

Slip Casting of Alumina Suspensions in a Strong Magnetic Field

Textured α‐alumina ceramics were processed by slip‐casting suspensions with different mean‐sized particles in a strong magnetic field of 9.4 T, followed by pressureless sintering at 1650°C for 2 h in air. The dispersed crystalline particles in the colloidal suspensions could be oriented in a strong magnet when the energy of the crystal anisotropy overcomes the thermal motion energy. According to the theoretical model, the energy of the crystal anisotropy increases with an increasing particle size, which was confirmed by the experimental results revealing that the orientation in the green deposit increased with the increasing starting powder size. After sintering, however, anisotropic grain growth accompanied with excellent texture formation was observed for the ceramic fabricated from the finest starting powder grade, whereas the modest orientation factor of the largest starting powder‐based ceramic hardly changed after sintering.

An investigation of the effect of processing conditions on the microstructure of vacuum plasma-sprayed Ti–Zr–Ni quasicrystal coatings

Ti41.5Zr41.5Ni17 (at.%) powders from two batches having different size fractions have been vacuum plasma sprayed to form coatings using different sets of spray parameters. The powders are composed mainly of the HCP alpha and Laves phases which transform to i-phase owing to rapid quenching during plasma spraying. The coatings are examined using image analysis, hardness tester, XRD, SEM, and TEM. TEM studies revealed that the coating has a microstructure constituted by extremely fine grains. It has been observed that the polycrystalline to i-phase transformation occurs in both coatings irrespective of the differences in starting powder size and other spray parameters.

The microstructure and mechanical property of alkaline earth-doped lanthanum gallate with Al&lt;sub align=right&gt;2O&lt;sub align=right&gt;3 addition

In the present paper, the microstructure and mechanical property of alkaline earth-doped lanthanum gallate with Al2O3 addition are studied and the effect of the starting powder size of Al2O3 is also discussed. The phase constitution is conducted by X-ray Diffractometry (XRD). The microstructure is observed by Scanning Electron Microscopy (SEM) and the ion electrical conductivity is measured by an impedance analyser. The results denote that the addition of 2% submicron Al2O3 can improve the bending strength obviously and has no influence on the ion electrical conductivity.

Growth kinetics of core-shell-structured grains and dielectric constant in rare-earth-doped BaTiO3 ceramics

The solute-drag-dependent growth kinetics of core-shell-structured grains in rare-earth-doped BaTiO3 ceramics was studied based on an analytical description of the diffusion of rare-earth atoms doped. Dependence of the sizes of grain core and shell on the sintering conditions, dopant content, and starting powder size was quantitatively revealed. The effective dielectric constant of the ceramics was calculated in terms of the relative contents of the ferroelectric core and paraelectric shell. The calculations are in good agreement with the experimental observations.

치밀층으로 코팅된 다공성 엔지니어링 세라믹스에서의 접촉응력에 의한 균열 거동

The engineering ceramic needs the properties of high strength, hardness, corrosion-resistance and heat-resistance in order to withstand thermal shock or applied nonuniform stresses without failure. The densely coated Porous ceramics can be used for machine component, eletromagnetic component, bio-system component and energy-system component by their high-performances from superior coating properties and light-weight characteristics due to the structure including pore by itself. In this study we controlled the porosity of silica and alumina, 8.2~25.4% and 23.4~36.0%, respectively, by the control of sintering temperature and starting powder size. We made bilayer structures, consisting of a transparent glass coating layer bonded to a thick substrate of different porous ceramics by a thin layer of epoxy adhesive, facilitated observations of crack initiation and propagation. The elastic modulus mismatch could be controlled using different porous ceramics as the substrate layer. Then we applied 150 N force using WC sphere with a radius of 3.18 mm by Hertzian indentation. As a result, the crack initiation in the coating layer was delayed at lower porosity in the substrate layer, and the damage in the coating layer was relatively smaller at the bilayer structure coated on higher elastic substrate.

Effect of starting powders size on the Al 2O 3–TiC composites

Al 2O 3–TiC composites with a content of 30 wt% TiC with various size of starting powders were manufactured by hot pressing. The Vickers hardness, bending strength and fracture toughness were studied. The experiment results show that the starting powder size has a significant effect on the properties of the Al 2O 3–TiC composites. The maximum bending strength of the submicron Al 2O 3 with the fine TiC powders addition is 712 MPa, while the maximum fracture toughness of the same Al 2O 3 matrix with the large TiC powders addition is 6.5 MPa m 1/2.

Effect of grain size on thermal shock resistance of Al 2O 3–TiC ceramics

In this paper, thermal shock resistance of pure hot-pressed alumina and Al 2O 3–TiC composites was studied. In order to assess the influence of Al 2O 3 and TiC starting powder size on thermal shock resistance, Al, Al 2O 3–TiC composites with different particle size were fabricated. The addition of TiC into alumina matrix remarkably improves the mechanical properties and thermal shock resistance. Decreasing grain size can improve the thermal shock resistance, and increase in density improves thermal shock resistance ever further. The critical thermal shock temperature difference (Δ T c) of Al 2O 3 (powder size 0.24 μm)–TiC (powder size 0.32 μm) composite is 100 °C higher than the Δ T c of monolith.

Significance of melt-fraction in HVOF sprayed hydroxyapatite particles, splats and coatings

Microstructure characterization and property evaluation of high velocity oxy-fuel (HVOF) sprayed hydroxyapatite (HA) splats and coatings were conducted in the present study as a function of the proportion of melting that occurred in HA particles during HVOF spray. In vitro behavior of single and folded HA splats in simulated body fluid was also investigated. Results showed that phase composition of as-sprayed HA coatings was influenced significantly by the melt fraction in HVOF sprayed particles. Melt fraction of the HA powders were experimentally determined from particle morphology analysis. It was found that the spray parameters and starting powder size influenced the melt fraction of the particles. In vitro investigation of individual HA splats made from different HA particles revealed decisive role of local phase composition in influencing their dissolution/precipitation behavior during the test. Furthermore, Raman spectroscopy qualitative inspection on the sprayed HA particles (partial melted) revealed that thermal decomposition occurred within the melted part rather than the unmelted zone. Young's modulus and micro-hardness of the as-sprayed particles and coatings were determined using nano-indentation technique. The resolidified zone of the sprayed HA particles exhibited an average Young's modulus value of 41.25 GPa. The measured values ranged from 23.1 to 65.3 GPa. The unmelted part of the HA powders showed a markedly narrower range. Young's modulus value of 83.9 GPa (±9.4 GPa) was recorded for this region. This succinctly highlight the difference between the unmelted region and melted regions of a HA particle. Young's moduli values measured on HVOF coatings were found to mirror the trend found in the spheroidised particles and splats with apt fidelity.

Effects of Starting Powder Size and Ball-Milling Time on Microstructure of WC-Co Base Cemented Carbides Prepared from W+C+Co Base Mixed Powder

We have already developed a new WC-Co base cemented carbides with highly oriented plate-like triangular prismatic WC grains by using W+C+Co base mixed powder instead of usual WC+Co base mixed powder, and then proposed the mechanism for the generation of such WC grains.In this report, the results on the effects of the starting-powder size and ball-milling time on the orientation degree of plate-like WC grains were mainly described. The orientation degree of plate-like WC grains became larger in the cases of coarser W and finer Co powders, and longer ball-milling of W, C and Co. These results could be explained, based on our previously proposed mechanism for the generation of highly oriented plate-like WC grains.

Deposition of highly adhesive ZrO 2 coating on Ti and CoCrMo implant materials using plasma spraying

ZrO 2 (4%CeO 2) and ZrO 2 (3%Y 2O 3) coatings were deposited on titanium (Ti) and CoCrMo implants using plasma spraying and the adhesive, morphological and structural properties of the plasma-sprayed coatings were evaluated. Characterization of these coatings was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness, hardness, and adhesive strength. XRD patterns showed that both the coatings appeared to be primitive tetragonal phase. SEM observations showed that both the ZrO 2 coatings appeared to be rough, porous and melted. The cross-section surface morphology of the coatings, coating–substrate interfaces and substrates without acid etching was very dense and smooth. After acid etching, as compared to the dense ZrO 2 coating–CoCrMo substrate interfaces, the thin gaps appeared within the ZrO 2 coating–Ti substrate interfaces. It is suggested that plasma spraying probably formed an amorphous Ti layer in the coating–Ti substrate interface that can be removed by acid etching. The average surface roughness of ZrO 2 (3%Y 2O 3) and ZrO 2 (4%CeO 2) coatings was correlated to the starting powder size and substrates. No significant difference between the hardness of all coatings and substrates was observed. The adhesive strengths of ZrO 2 (4%CeO 2) coating to Ti and CoCrMo substrates were higher than 68 MPa and significantly greater than that of ZrO 2 (3%Y 2O 3) coatings.

The role of starting powder size on the compressive response of stand-alone plasma-sprayed alumina coatings

Cylindrical stand-alone tubes of plasma-sprayed alumina were tested in uniaxial compression at room temperature, using strain gages to monitor axial strains. The effect of lamella size on the mechanical response was investigated by employing different starting powders to fabricate samples. The average powder sizes investigated included 9 μm, 19 μm and 32 μm alumina; the resulting effective lamella diameters were 10 μm, 28 μm, and 55 μm, respectively. Similar stress-strain hysteresis was observed on unloading in all tubes, independent of lamella size. A strong correlation between the failure stress and the cumulative strain at failure was also observed for tubes fabricated from the three powders. For samples with approximately constant densities, tubes plasma sprayed with the 9 μm powder exhibited greater moduli than tubes sprayed from either 19 or 32 μm powders. This difference was attributed to the greater percentage of unmelted α-Al2O3 in the coating.