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Microstructure and Mechanical Properties of Silicon Nitride Ceramics with Controlled Porosity
Author(s) -
Yang JianFeng,
Ohji Tatsuki,
Kanzaki Shuzo,
Díaz Aranzazu,
Hampshire Stuart
Publication year - 2002
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2002.tb00305.x
Subject(s) - porosity , materials science , flexural strength , microstructure , fracture toughness , composite material , sintering , ceramic , silicon nitride , grain size , modulus , hot pressing , layer (electronics)
Porous silicon nitride ceramic with a porosity from 0–0.3 was fabricated by partial hot‐pressing of a powder mixture of α‐Si 3 N 4 and 5 wt% Yb 2 O 3 as sintering additive. Irrespective of the porosity, the samples exhibited almost the same microstructural features including grain size, grain aspect ratio, and pore size. Porosity dependences of Young's modulus, flexural strength, and fracture toughness ( K I C ) were investigated. All these properties decreased with increasing porosity. However, because of the fibrous microstructure, the decreases of flexural strength and fracture toughness were moderate compared with the much greater decrease of Young's modulus. Thus, the strain tolerance (fracture strength/Young's modulus) increased with increasing porosity. The critical energy release rate also increased slightly with an increasing volume fraction of porosity to 0.166 and remained at the same level with that of the dense sample when the porosity was 0.233. They decreased as porosity increased further.