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Microstructures and Properties of Mo 5 Si 3 ‐Particle‐Reinforced Si 3 N 4 ‐Matrix Composites
Author(s) -
Iizuka Tateoki,
Murao Toshihiro,
Yamamoto Hiroyuki,
Kita Hideki
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.tb00198.x
Subject(s) - materials science , flexural strength , fracture toughness , composite material , grain boundary , molybdenum , microstructure , sintering , composite number , ceramic , chemical vapor infiltration , hot pressing , molybdenum disilicide , ceramic matrix composite , metallurgy
Mo 5 Si 3 ‐particle‐reinforced Si 3 N 4 ‐matrix composites were fabricated by sintering molybdenum‐solution‐infiltrated porous Si 3 N 4 . Fine Mo 5 Si 3 particles, with an average diameter of ∼0.13–0.17 μm, grew in situ from the reaction between MoO 3 and Si 3 N 4 in the grain boundary of the Si 3 N 4 . The Mo 5 Si 3 particles resided in the grain‐boundary glassy phase and reinforced the grain boundaries. The four‐point flexural strength and fracture toughness of a 2.8 wt% Mo 5 Si 3 ‐Si 3 N 4 composite were 1060 MPa and 7.7 MPa·m 1/2 , respectively. This was higher than those for normally sintered Si 3 N 4 by ∼17% and ∼18%, respectively. The fracture toughness of the Mo 5 Si 3 ‐Si 3 N 4 composite increased as the content of Mo 5 Si 3 particles increased, but the flexural strength decreased. Improvement in fracture toughness was attributed to a thermal expansion mismatch among the Mo 5 Si 3 , the Si 3 N 4 , and the grain‐boundary amorphous phases in the Mo 5 Si 3 ‐Si 3 N 4 composites. Another reason for the improved fracture toughness was the pullout of elongated Si 2 N 2 O grains that formed as a result of oxygen gas released from the reaction between the molybdenum‐solution‐obtained MoO 3 and the Si 3 N 4 . The infiltration method for incorporating desired elements or compounds into a ceramic matrix holds promise as a process for fabricating submicrometer‐ or nanometer‐sized composites with high strength and high fracture toughness.