Microstructure in silicon nitride containing β-phase seeding: Part I

Abstract

A proper powder preparation technique was used to develop elongated ␤-Si 3 N 4 particles as seeds from raw materials. The phase transformation and development of microstructure in Si 3 N 4 ceramics containing ␤-Si 3 N 4 seeds were investigated. The specimens of seeded silicon nitride had higher phase transformation rates than the specimens without seed. A core/shell structure was observed by transmission electron microscopy in seeded specimens owing to the difference in aluminum concentration in Si 3 N 4 grains. The misfit between the core and the shell was accommodated by interfacial dislocation that has a rotation character. The growth mode was epitaxial, although there was some compositional difference between the core and the shell. A relatively larger grain size and wider grain size distribution in seeded Si 3 N 4 specimens was due to the amount of ␤-phase seeds that could act as the nuclei, and the final modification of the microstructure was due to the coalescence process. The crack wake process characterized the mechanism of toughening.

Microstructure in Silicon Nitride Containing β‐Phase Seeding: III, Grain Growth and Coalescence

“…The distinctive contrast between the core and shell structures resulted from differences in the chemical composition and misfit strain, as discussed previously. 1 Figure 2(a) is a typical bright-field TEM micrograph of the sample shown in Fig. 1.…”

“…1,2 In the present investigation, the remaining ␤-phase seeds and the surrounding microstructure were examined by transmission electron microscopy (TEM) to clarify the growth process of the seeds. The structural defects and characteristics of the sintered grains also were examined.…”

Preparation of rod-like β-Si3N4 seeds with tailored morphology

“…The addition of β-Si 3 N 4 seeds into Si 3 N 4 ceramics could promote α-to β-phase transformation [1,2], and improve the fracture toughness, fracture strength, and thermal conductivity [2][3][4][5][6][7]. The β-Si 3 N 4 seeds are prepared by: (1) the heat treatment of α-Si 3 N 4 powders with or without additives [8][9][10][11][12];…”

Variation of sintering parameters at an early stage of densification affecting β-Si3N4-microstructure

“…9,10 Therefore, commercial Si 3 N 4 -ceramics are manufactured using powders with a high ␣-Si 3 N 4 content. A large amount of ␤-Si 3 N 4 accelerates the ␣-␤-transformation during the liquid-phase sintering processs, [11][12][13] but typically yields a rather fine equiaxed microstructure. Doping with fine ␤-Si 3 N 4 -needles increases the number of elongated ␤-Si 3 N 4 -grains as well as their aspect ratio.…”