Formation mechanism of porous reaction-bonded silicon nitride with interconnected pores in the presence of MgO

In porous reaction bonded silicon nitride, whiskers normally grow in globular clusters as the dominant morphology and deteriorate the pore interconnectivity. However, the ceramic microstructure was significantly transformed with the addition of MgO; specifically, the morphology was modified to a combination of matte and hexagonal grains. Microstructural observation along with thermodynamic studies suggest that MgO interfered with the presence and nitridation of SiO(g). Consequently, rather than being involved in the whiskers’ formation, surface silica instead reacted with volatile MgO to form intermediate products. Through these reactions, whisker formation was blocked, and a porous interconnected structure formed which was confirmed by 3D tomography. After heat-treatment at 1700 °C, β-Si3N4 crystallized in a glassy matrix containing magnesium. Resulting samples had an open-pore structure with porosity of 74-84 vol. %, and density of 0.48-0.75 g.cm-3. Combination of high porosity and pore size of <40 μm led to compressive strengths of 1.1 to 1.6 MPa

Effect of Sn on the Dehydrogenation Process of TiH2 in Al Foams

The study of the dehydrogenation process of TiH2 in aluminum foams produced by the powder metallurgy technique is essential to understanding its foaming behavior. Tin was added to the Al foam to modify the dehydrogenation process and stabilize the foam. A gradual decomposition and more retention of hydrogen gas can be achieved with Sn addition resulting in a gradual and larger expansion of the foam

Titanium-based composites produced by powder metallurgy

Titanium-based metal-matrix composites, reinforced with ceramic particulates, have considerable potential for improvements in properties and service temperature, while retaining isotropic behaviour and ease of fabrication using conventional processing methods. However, the potential of titanium based composites can be limited by the extreme chemical reactivity of titanium with most ceramic materials which can result in the formation of a chemical reaction product at the matrix/ceramic interface. In this work, Ti-6%Al-4%V/TiC particle reinforced composites were fabricated using elevated temperature sintering and/or deformation processing.Peer reviewed: YesNRC publication: Ye