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Influence of the Metal Particle Size on the Crack Growth Resistance in Mullite–Molybdenum Composites
Author(s) -
Bartolomé José F.,
Díaz Marcos,
Moya José S.
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.tb00528.x
Subject(s) - materials science , composite material , mullite , grain size , bridging (networking) , fracture toughness , ceramic , indentation , composite number , molybdenum , particle size , fracture mechanics , grain boundary , toughness , microstructure , metallurgy , computer network , chemistry , computer science
The R ‐curve for mullite–molybdenum (32 vol%) composites, which were obtained at 1650°C under reducing conditions with three different Mo average grain sizes (1.5, 3, and 9 μm), was estimated by the indentation‐strength method and compared with that monolithic mullite obtained under similar conditions. The composites material exhibited rising R ‐curve behavior. The composite with larger grain size, however, displayed better damage tolerance and higher resistance to crack growth. Microscopic observation of the crack path revealed, in the composites, the systematic presence of dispersoids acting as bridging sites in the crack wake. Therefore, the increased fracture toughness of these ceramic‐matrix composites with adherent ductile phase can be attributed to clamping forces applied by metal ligaments that bridge the crack faces behind the crack front. These clamping forces retard the crack from opening as an external stress is applied. It was inferred that this superior performance of the larger Mo particle size composite can be attributed mainly to more effective bridging of the metal grains. Because of this, a higher applied stress intensity will be required to propagate the crack tip. These results suggest that the rising R ‐curve should be proportional to the metal grain size, since the grain bridging area is proportional to the metal grain size.