Papers by Keyword: Sintering

Abstract: Solid Oxide Fuel Cells (SOFCs) are among the most promising clean energy technologies, yet their widespread commercialization is hindered by high operating temperatures, material degradation, and cost challenges. Recent advances in anode, cathode, and electrolyte materials have enabled SOFCs to operate efficiently at intermediate temperatures (500–800 °C), thereby reducing thermal stress and manufacturing costs. For instance, gadolinium-doped ceria (GDC) has demonstrated up to three times higher ionic conductivity than yttria-stabilized zirconia (YSZ) at 600 °C, while perovskite-based cathodes such as LSCF (La₀.₆Sr₀.₄Co₀.₂Fe₀.₈O₃−δ) exhibit superior catalytic activity and stability compared to conventional lanthanum manganite. This review critically analyzes the progress in SOFC material development, highlights key fabrication strategies such as spin coating and advanced thin-film deposition, and evaluates techno-economic considerations for scaling up. The study also outlines future research directions including nanostructuring, hybrid electrolytes, and durability testing to accelerate commercialization.

Abstract: This study explores the impact of heat treatment parameters on the hardness and microstructure of 17-4PH stainless steel samples fabricated by additive manufacturing, with a focus on dimensional changes throughout the process. The additive manufacturing method used was Bound Metal Deposition (BMD), which includes digital scanning, 3D metal printing, sintering, and post-processing. It was observed that the printed parts undergo a substantial size increase 16.96% (height) and 18.14% (diameter) to compensate for material loss during the binder removal stage in sintering. Although the sintered parts shrink relative to the printed samples, they remain 3.25% taller and 6.05% wider than the original CAD dimensions. Following sintering, the samples underwent solution treatment and aging at various temperatures and times. Microstructural analysis post-solution treatment revealed a martensitic structure as the predominant phase. Aging caused the formation of strengthening precipitates, leading to peak hardness values of 422.0 and 303.0 HV0.5 at aging temperatures of 480 °C and 620 °C for 1 hour, respectively. Dimensional changes during the precipitation hardening stage were minimal and considered negligible.

Abstract: Alumina (Al₂O₃) is a technical ceramic widely selected for demanding applications due to its excellent material properties, such as high strength, corrosion resistance, and thermal stability. In this study, the effect of the sintering temperature of 3D-printed alumina to its surface characteristics and its subsequent performance as a copper-metallized ceramic substrate was investigated. Green parts of alumina samples were prepared using stereolithography (SLA) 3D printing, debound, then sintered at temperatures ranging from 1660°C to 1740°C. Surface roughness was quantified using Atomic Force Microscopy (AFM), while the copper layer's adhesion was assessed via tape and burnishing tests. Electrical conductivity was measured with a four-point probe. A non-monotonic relationship between sintering temperature and surface roughness was observed. Roughness (Ra​) decreased as temperature increased from 1660°C to 1720°C, attributed to enhanced densification. However, increasing the temperature to 1740°C led to grain coarsening and a slight increase in roughness due to excessive grain growth. Stronger copper adhesion was achieved on smoother surfaces produced at optimized sintering temperatures. Electrical conductivity was also determined with a minimum sheet resistance of 0.089 mΩ/sq achieved.

Abstract: The aim of the study was to prepare samples suitable for testing the shape memory phenomenon in ceramic systems. Testing would be carried out by preparing micro-objects with dimensions in the order of micrometers using SEM/FIB techniques, and subsequent testing using a nanoindenter. The article deals with the influence of the preparation method on the properties of samples prepared by conventional annealing and spark plasma sintering. Two commercial powders were used, namely PSZ-10C and PSZ-20C. The microstructure of the samples, fracture surfaces and HV hardness, as well as indentation hardness were evaluated on the prepared samples. It was shown, that both conventional annealing and SPS can be used for preparation of samples with a suitable grain size, but also that the preparation method has a significant impact on the properties of the sample. Depending on the preparation method, the grain size varied from approximately 1 μm to 50 μm. There is also difference in the character of the fracture surfaces and in the hardness of the samples, where a difference in indentation hardness from approximately 10 GPa to approximately 20 GPa was measured.

Abstract: The different characteristics of nanoparticles (NPs) are mostly determined by the sintering process. The goal of the current study is to examine how the sintering temperature affects the optical and structural characteristics of Y₂O₃ NPs made using the sol-gel method. For a competitive study, the synthesized Y₂O₃ NPs were sintered for three hours at 300, 600, and 900°C. The generated Y₂O₃ NPs were sintered for three hours at 300, 600, and 900°C in this work. Samples of Y₂O₃ NPs are designated Y1, Y2, Y3, and Y4, in that order. The cubic structure of Y₂O₃ NPs is confirmed by XRD examination, which also corresponds to JCPDS card No. 083-0927. For Y1, Y2, Y3, and Y4, the crystallite sizes were determined to be 12.58, 12.24, 12.05, and 09.16 nm, respectively. The optical characteristics, such as energy bandgap fluctuations and light absorption, were investigated using UV-Vis spectroscopy. Usually, the absorbance peak shows up between 230 and 250 nm. For Y1, Y2, Y3, and Y4, the energy band gap was determined to be 4.51, 4.40, 4.31, and 4.19 eV, respectively. The vibrational modes of the Y₂O₃ NPs are examined, which provides further evidence of phase purity and structural stability. Increased band gap, better crystallinity, and a lower percentage of oxygen atoms all help the material's mechanical and chemical durability as well as its shine, which makes it more suitable for dental ceramic applications.

Abstract: The powder bed fusion with electron beam (PBF-EB) process is characterised by a preheating step that keeps the building temperature high and produces partial sintering of the metallic powder particles. The influence of the preheating parameters can be studied through numerical simulations, such as those conducted with the phase field (PF) method. PF can describe the neck formation among the particles under the sintering mechanisms. In this regard, PF simulations usually account for the diffusion mechanisms only, neglecting the rigid body motion (RBM), particularly during PBF-EB. The current work analyses the effect of RBM on neck formation and growth among particles subjected to the typical working conditions of a PBF-EB. Owing to the lack of literature, the parameters that describe the rigid translation of the particles undergoing the sintering are identified using a structured design of numerical experiment. Including the RBM during sintering produces a larger neck among the particles and faster densification. This result has been found in agreement with the current literature. However, the decision to include or not the RBM should be adequately waited, considering that in the current study including RBM increased the simulation time. The results revealed that each parameter plays a different role in the rigid translation of the particles, causing a different neck dimension.

Abstract: Crack propagation behavior is a critical factor influencing the service life of thermal barrier coatings (TBCs). With the use of hydrogen as a fuel in a carbon-neutrality context, incomplete combustion of hydrogen gas will introduce potential new failure modes for TBCs. Therefore, it is crucial to evaluate the crack propagation behavior of TBCs subjected to a hydrogen environment. In this study, in-situ three-point bending tests were used to investigate the crack propagation behavior within the top coat after heat treatment under air and hydrogen environments. The results reveal that the sintering degree is reduced after heat treatment in hydrogen environments, accompanied by the formation of numerous microcracks before the displacement reaches 0.6mm. Conversely, heat treatment in air environments results in a higher sintering degree and promotes the propagation of main vertical cracks on the surface of the top coat as the displacement gradually increases to 0.8 mm. Additionally, this study discusses the effect of sintering on the fracture toughness of the top coat and further elucidates the effect of hydrogen fuel on the overall durability of TBCs.

Abstract: Metal matrix composites (MMCs) have received considerable attention due to their low density with good elastic modulus and high strength to weight ratio. Discontinuous reinforced Ti matrix composites have been found as a promising material for applications in various fields, such as aerospace, automotive, biomedical and advanced military applications, because of their low cost, improved performance and ease of fabrication. Among the discontinuous ceramic reinforcements, TiC is identified as a very suitable reinforcement for the Ti system because of its excellent properties and high compatibility with Ti matrices. In this study, investigations have been conducted on the influence of volumetric percentage of TiC (10%) on microstructural development of TiC reinforced titanium beta matrix composite prepared by the blended elemental method from hydrided powders using ex situ processing route. Samples were produced by mixing of elemental hydrided powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering (900°C- 1500°C), in high vacuum. Sintered samples were characterized for phase composition, microstructure, microhardness and mechanical properties by X-ray diffraction, scanning electron microscopy, Vickers indentation, respectively. Density was measured by Archimedes method. The experiment results revealed that TiC content has significant influence on the microstructure and improving the hardness values of Ti-35Nb-TiC composites. A homogeneous distribution of TiC particles was observed, with a reduced presence of agglomerates and macroporosities. There was an increase of 28.5 % in the hardness of the composites with the addiction of TiC, which indicates the possibility of using components manufactured using this technique, for example, in aircraft landing gears that are subject to high mechanical stress and orthopedic implants.

Abstract: The characteristics of β-phase metastable Ti alloys make them an attractive choice for advanced engineering applications in demanding conditions. Ti-35Nb alloy has high strength-to-weight ratios, deep hardenability and high biocompatibility exhibiting high potential for use in niche applications for aircraft structures, orthopedic implants, and orthodontic devices. The difficulty of producing complex shapes of these alloys by conventional methods for reasonable costs makes Metal Injection Moulding (MIM) attractive. Sintering behavior, microstructure and mechanical properties of a Ti–35Nb alloy processed by MIM technology from hydrided powders were investigated in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermal and microhardness analysis. Samples with relative density up to 93% have been produced using a feedstock based on wax-polymer binder. The microstructural evolution observed during sintering from 900 °C up to 1500 °C indicates a combination of densification and optimized microstructure reached because of the complete dissolution of the β stabilizer (Nb) in the titanium matrix. The injection and sintering parameters provided a homogeneous microstructure with some TiC precipitates at grain boundaries and relative high porosity. Higher sintering temperatures or longer holding times can lead to intensive grain growth.

Abstract: This study delves into the nuanced challenges of additive manufacturing, specifically focusing on the application of sinter-based processes for reactive materials, with Titanium as the focal point. The thermal debinding and sintering processes, crucial steps in shaping, are analyzed with an emphasis on the intricate control required for the removal of polymeric binders, especially concerning the reactivity of metals during these processes. Historically, the emphasis has been on materials like 316L and 17-4-PH due to their straightforward thermal debinding and sintering processes. However, the shift to Titanium and its alloys introduces complexities, requiring special debinding and meticulous control of interstitial elements such as C and O to adhere to stringent material standards such as ASTM F2885-17. This research examines the various stages of shaping progressions, addressing specific requirements like green part strength, flexibility (filaments), flowability (Metal Injection Molding), and crosslinking (Stereolithography). The focus lies on achieving thermal removal with minimal residuals and reactivity, particularly in the context of reactive metals. Lithography-Based Metal Manufacturing (LMM) and Cold Metal Fusion (CMF) emerge as significant additive manufacturing processes for small to medium-sized batches of titanium parts, utilizing sinter-based production setups. Both processes not only serve as alternatives to Metal Injection Molding but also contribute to cost-effectiveness and sustainability through the efficient reuse of unused feedstock. The selection of the optimal shaping technology for individual parts becomes critical, considering mechanical properties, final density, acceptance of interstitials, complexity, wall thickness, overhangs, and internal structures. This presentation provides a detailed analysis of Lithography-Based Metal Manufacturing, comparing it with the Cold Metal Fusion process. Key considerations include mechanical properties, surface finishes, and cost, shedding light on the technical intricacies and trade-offs inherent in each technology.