Oxide-induced fast densification in W alloys

Kinetics of alloy formation and densification in Fe-Ni-Mo microfilaments extruded from oxide- or metal-powder inks

Gadolinia-doped ceria nanopowder was prepared by glycine-nitrate combustion method with different glycine/nitrate mixing ratio. The characteristics of the synthesized powder were investigated by X-ray diffraction method, transmission electron microscopy, thermal gravity, differential thermal analysis and thermo-mechanical analysis. The smallest powder was obtained with glycine/nitrate ratio 1.00 and the lowest organic and water vapor contained powder was made with glycine/nitrate ratio 1.75. According to dilatometry, fast densification was occurred around 1000℃ and shows full density over 1300℃. Finally near-fully dense ceria electrolyte was fabricated with conventional sintering technique. Glycine-nitrate process yields fine nanopowders which enable low temperature sintering and fabrication of fully dense and nanostructured oxide electrolyte.

Os pós à base de óxido de estanho são conhecidos por apresentarem baixa densificação mesmo a temperaturas de sinterização acima de 1500 °C. A introdução de diferentes íons metálicos como Mn2+, Fe3+ e Cu2+ induzem a redução do volume de poros e crescimento de grãos durante a sinterização. Pós à base de SnO2 foram preparados pela rota química derivada da patente de Pechini, contendo diferentes concentrações de Mg2+ ou Fe3+. Todas as amostras apresentaram uma alta taxa de densificação nos momentos iniciais, quando sinterizadas por "fast firing". As amostras contendo 5% em mol de ferro sinterizadas durante 30 s a 1200 °C apresentaram densidades superiores às amostras sinterizadas por aquecimento em taxas normais (10 °C/min) por 4 h a 1200 °C. O fenômeno de eliminação rápida de poros pode ser explicado, levando em conta o papel da superfície no fenômeno de sinterização. A saturação da superfície pelo aditivo foi confirmada por medidas de mobilidade eletroforética dinâmica com base na literatura e em dados experimentais.

Evolution of the pore structure of a ceramic powder compact during sintering

Influence of spark plasma sintering conditions on microstructure, carbon contamination, and transmittance of CaF2 ceramics

The study provides a novel way for the utilization of coal fly ash, and enriches the sintering mechanism in preparation of low-cost, high performance mullite based ceramic. The phase evolution, microstructure, densification behavior and flexural strength as a function of the sintering temperatures, were investigated by XRD, SEM and evaluated by density, open porosity and shrinkage and three point bending method, respectively. Secondary mullite nucleates from the dissolution of alumina in transient liquid phase at 1300°C. Above 1400°C, mullite content increases and the densification is promoted with increasing temperature. Fast densification takes place and high flexural strength of 149MPa is achieved at 1600°C.

The research objective of the study was to increase the current understanding about how oxide compositions (CaO, MgO and SiO2 ratios) influence the (1) crystallization behaviour of starting frits, and subsequently (2) morphological features of diopside crystals, formed after wall tile industrial firing. It has been shown that the replacement of CaO and MgO at the expense of SiO2 causes a decrease in the crystallization temperature. The increase of CaO content also results in lower softening temperature and faster densification. SEM results of the glazes showed that spherical and needle-shape diopside crystals were formed during heating. While increase of MgO content results in finer needle-shape crystals, increase of CaO results in coarser spherical-shape crystals. Although all the glaze formulations showed a high whiteness index, lower densification and higher crystallization in the glazes caused an unfired matt appearance.

Sintering of nanoparticle inks over large area-substrates is a key enabler for scalable fabrication of patterned and continuous films, with multiple emerging applications. The high speed and ambient condition operation of photonic sintering has elicited significant interest for this purpose. In this work, we experimentally characterize the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. It is shown that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. Further, high densification can be achieved even without nanoparticle melting. Electromagnetic Finite Element Analysis of photonic heating is coupled to an analytical sintering model, to examine the role of interparticle neck growth in photonic sintering. It is shown that photonic sintering is an inherently self-damping process, i.e., the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached. By accounting for this phenomenon, the developed coupled model better captures the experimentally observed sintering temperature and densification as compared to conventional photonic sintering models. Further, this model is used to uncover the reason behind the experimentally observed increase in densification with increasing weight ratio of smaller to larger nanoparticles.

Densification of 0·99SnO20·01CuO mixture: Evidence for liquid phase sintering

In order to unclose the dynamics of SPS densification, a special sintering sample (Cu/Ti wires compact) was designed. Characters of the shrinkage rates during sintering process and microstructures of products fabricated by the spark plasma sintering (SPS) and hot-press sintering were investigated. The experimental results reveal that a higher temperature field is formed at the connected area and conductive net of the compact. These high-temperature parts deformed more easily than other parts, which is believed to be the main cause of SPS fast densification, according to a hard-core and soft-hell material model.

Solid-state sintering is one of the most widely used material processing technologies in modern manufacturing. The preponderance of previous computer simulations focused on free sintering (without externally applied pressures), in which the morphology evolution and densification in the system are driven by surface energy reduction. In this work, we develop an efficient algorithm to simulate solid-state sintering with hot pressing by explicitly considering interfacial diffusion as well as rigid body movement under external pressure. Particle movements including both translations and rotations are taken into account in the model, which are directed by the associated local stress state in the sintering system. A novel “geometric force” is also introduced to stochastically model geometrically necessary plastic deformations of the sintering particles to accommodate the initial fast densification due to the applied pressure. Subsequent evolution of the overall morphology and inter-particle connections are mainly controlled by interfacial energy minimization, while coarsening is considered in the later sintering stages. The utility of our method is illustrated by sintering 2D compacts of polydisperse circular particles and equal-sized elliptical particles. Significant coarsening occurs in the polydisperse particle system, while no significant grain growth is observed in the equal-sized ellipse system.

Fast densification of dense nano-grained Gd2Zr2O7 ceramic prepared by two-step microwave sintering

The use of powder metallurgy for near net shape sintering of superalloy could lead to major savings in machining time and material. The main challenge in sintering Inconel 718 is to avoid the formation of a prior particle boundary (PPB) network that is deleterious to the mechanical properties. Using the Spark Plasma Sintering (SPS) technique, it is believed that Inconel 718 powders could be sintered without forming a PPB network due to the fast heating rate achieved and the reported cleaning effect of particle surfaces by the interparticle arc discharges. In this study, Inconel 718 was consolidated to near-full density at 1200°C under 50 MPa of pressure with heating rates ranging from 20°C/min to 800°C/min. The densification behavior of the powder was studied through the analysis of the densification curves and observation of the microstructure evolution from interrupted tests. The fast densification of Inconel 718 in SPS was linked to the formation of a supersolidus liquid phase due to the nature of the heating in this technique.