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Item type:Publication, Access status: without files , Stabilization of porosity in reaction bonded aluminum oxide (RBAO) by coarsening in a reactive atmosphere(Elsevier, 2024-10-01); ; ; A coarsening treatment in an HCl containing atmosphere was performed to stabilize the porosity of Al2O3/ZrO2 composites up to elevated temperatures. There is minimal shrinkage during the reactive coarsening treatment and the porous microstructure is stable during subsequent heat treatments. The reaction bonding of aluminum oxide (RBAO) process was used to fabricate the samples. Coarsening was investigated as a function of initial density (40–60 % TD) and coarsening temperatures (1250–1400 °C). After the HCl coarsening step, samples were sintered in air to determine the effect of coarsening treatment on pore stability. Up to the temperature of the coarsening treatment no further densification is observed. Above the HCl coarsening temperature densification is significantly retarded. Thus, it is shown that the porosity in RBAO can be stabilized by heat treatment in a 10 vol % HCl containing atmosphere. During the coarsening treatment in HCl at 1300 °C, 1350 °C and 1400 °C little densification was observed (Δ ρ ≤ 2 % TD) in comparison with the densities that result from sintering reaction bonded samples in air at 1350 °C (Δ ρ ∼ 5–8 % TD). Therefore, the HCl coarsening is a promising approach to adjust a desired level of porosity for high temperature applications of porous materials. It is postulated that at a given density, the coarsened materials should exhibit increased strength compared to un-coarsened materials due to increased contact area between the particles.Publicationtype: Journal Article21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Preparation and characterization of fine-grained (Mg, Y)-PSZ ceramics with spinel additionsA fine-grained Mg-PSZ-type material has been produced by adding MgAl2O4 spinel to a ternary Y2O3-MgO-ZrO2 alloy. A mean cubic grain size below 10 μm was achieved. Aging treatment at 1100°C and 1400°C lead to the formation of transformable tetragonal precipitates and resulted in improved toughness. Transformation toughening is the main toughening mechanism.Publicationtype: Book Part5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reaction-Forming of Ceramic Composites Using Metallic AluminumReaction synthesis offers affordable routes to fabricate homogeneous, fine-grained materials with advanced properties suitable for applications at room and elevated temperature. This chapter concentrates on syntheses using metallic aluminum to form alumina-containing composites. Powder metallurgical and casting/infiltration techniques are used with Al reacting in the solid and liquid states. The reaction techniques outlined were analyzed and developed at the Technical University at Hamburg in collaboration with partners outside. The variability potential in view of raw materials, processing parameters, microstructural tailorability, and shaping capability is discussed.Publicationtype: Book Part72 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mikromechanische Bewertung aluminothermisch hergestellter Schneidstoffe(Technische Universität Hamburg, 2002); ; ; ; Publicationtype: Report6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fracture behaviour in metal fibre reinforced ceramics(1997); ; ; ; The aim of the work is to gain a better understanding of the microprocesses involved in the fracture of ductile phase reinforced CMCs with an interpenetrating network microstructure, especially the processes involved in deformation and fracture of the ductile phase and its subsequent influence upon overall mechanical performance of the material. A model material is produced comprising regularly orientated aluminium fibres located within an alumina matrix. Compact tension samples, each produced with fibres orientated at 30°, 60° or 90° to the fracture plane, are used to produce crack growth resistance curves and are then sliced to produce samples which are used to test the stress-extension, σ(u), behaviour of the ductile fibres. Fracture surfaces are analysed within the SEM. The σ(u) behaviour and fracture process of the fibres is modelled using both a dislocation pile-up model and FEM analysis. Comparison is made with a geometric ductile deformation model from the literature. The models are found to describe well the σ(u) experimental data and also the crack growth resistance results. It is found that ductile phase deformation and fracture is highly sensitive to the level of mechanical constraint upon the fibre. This is influenced by factors such as the porosity in the fibre, the interface strength and fibre orientation relative to the crack plane. Fibre diameter significantly affects σ(u) behaviour also.Publicationtype: Journal Article17