Characterization of Sintered Niobium–Alumina Refractory Composite Granules Synthesized by Castable Technology

Zienert, Tilo; Brachhold, Nora; Weiner, Max; Schmidtchen, Matthias; Prahl, Ulrich; Aneziris, Christos G.

doi:10.1002/adem.202200407

Cited by 4 publications

(3 citation statements)

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“…The classification of the particles in several size classes has the benefit of controlled mixing of different particle sizes to obtain optimal results in sintering behavior and final product properties. Details of the procedure are described in Zienert et al [9,10]. The shape parameters of a given particle were obtained by fitting the shape function (Equation 1) on the particle's contour line.…”

Section: Methodsmentioning

confidence: 99%

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

Weiner,

Zienert,

Schmidtchen

et al. 2023

SSP

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In sintering simulation, there are basically two approaches: microscale simulation, in which distinct particles or pores are regarded, and macroscale, where the porous body is regarded as continuum with variable density.Material parameters of the latter can be determined by experiment or by microscale models.Current microscale sintering models mainly use circular resp.~spherical particle geometries to represent the actual shape of real particles.However, sintering behavior is heavily dependent on the morphology of the powder particles, since sintering progress is driven by reduction of the bound surface energy.So current models neglect the influence of local contact morphology.Here, a finite differences based microscopic sintering model is presented, which is capable to work with irregular particle geometries.Asymmetric particle contacts in shape and substance are possible within.The differences between circular particle contacts and asymmetric ones are investigated.Furthermore, a statistical way of describing the morphology of powder particles and its inclusion into sintering simulation using Monte Carlo techniques are shown.Morphology data are obtained from microscopic imaging by extracting the 2D contours.The particles' contour lines are fitted to a parameterized shape function including ovality and first order waves to obtain a description of the particles' fine shapes.From the statistical distribution of the shape parameters, randomized particle groupings are sampled as input for microscopic sintering simulation.Statistical analysis of the samples' sintering behaviors leads to statements about the powder's.Comparisons to classical spherical modelling are given.

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Section: Methodsmentioning

confidence: 99%

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

Weiner,

Zienert,

Schmidtchen

et al. 2023

SSP

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“…The powders analyzed in this work were the same as in Zienert et al [41,42] The powders in question consist of presintered material that was crushed and sieved. Therefore, the regarded particles are aggregates and the different sieve classes are also called aggregate classes.…”

Section: Powder Materialsmentioning

confidence: 99%

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles—Part II: Statistical Powder Modeling

et al. 2022

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Current simulations of sintering processes work often with heavily idealized powder geometries. As sintering is mainly driven by gradients of chemical potential due to surface curvatures, a realistic description of the particle geometry is essential for achieving precise simulation results. In previous work, a model able to simulate sintering behavior of irregularly shaped particles was shown. Herein, a statistical approach for description of particles’ morphology in a powder mixture is developed by fitting a simplified particle shape model on image data. The obtained data are analyzed and conditioned for input into sintering simulation. Instead of building an equivalent volume cell of particles, as common, a Monte Carlo approach is applied to describe the sintering behavior of the powder. The resulting distributions of sintering time curves are analyzed regarding the influence of the morphology description in comparison to circular particles. Using thumb rules of Cohen's effect size, a small effect on shrinkage and a medium effect on neck radii is observed.

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“…A novel approach in the field is the development of coarse-grained (particle sizes of up to a few mm) ceramic-metal composites [6,[11][12][13] to improve creep and thermal shock resistance compared to fine-grained composites. Heat treatments during manufacturing such as sintering can cause reactions of the involved phases with each other or with the environment, which will inevitably affect the properties of the composite.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Oxide Formation at α‐Al₂O₃–Nb Interfaces

et al. 2023

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Parts for metallurgical applications made from refractory metal–ceramic composites offer improved thermal shock resistance due to their capability for resistive heating compared to ones made solely from ceramics such as Al2O3. The combination of Al2O3 and Nb is intriguing as both show similar thermal expansion behavior over a wide temperature range. The high affinity of Nb for O to form nonprotective oxides, however, hampers its use in oxidative environments. Formation of such phases at the ceramic–metal interface can have detrimental effects on the cohesion of the composites. For this work, nanocrystalline Nb films are deposited on sapphire substrates by magnetron sputtering to study diffusion of O and high‐temperature phase formation at a refractory metal–ceramic interface during heat treatment under Ar at 1600 °C. A combined approach of atom probe tomography and transmission electron microscopy for compositional and crystallographic analyses reveals that at triple junctions of the sapphire–Nb interface with Nb grain boundaries, heterogeneous nucleation of nanoscale NbO2 occurs, which further reacts with Al2O3 to form AlNbO4, while the Nb film itself remains metallic. Fast O transport through grain boundaries leads to internal oxidation at the interface, whereas regions further away from Nb grain boundaries remain unchanged.

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Characterization of Sintered Niobium–Alumina Refractory Composite Granules Synthesized by Castable Technology

Cited by 4 publications

References 30 publications

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles—Part II: Statistical Powder Modeling

Nanoscale Oxide Formation at α‐Al₂O₃–Nb Interfaces

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Characterization of Sintered Niobium–Alumina Refractory Composite Granules Synthesized by Castable Technology

Cited by 4 publications

References 30 publications

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles—Part II: Statistical Powder Modeling

Nanoscale Oxide Formation at α‐Al2O3–Nb Interfaces

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Nanoscale Oxide Formation at α‐Al₂O₃–Nb Interfaces