Ceramic fracture mode-intergranular vs transgranular fracture

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:535631

Rice, R W

Available data on intergranular fracture (IGF) vs transgranular fracture (TGF) of ceramics is summarized and significantly extended. At 22 C, where there is most data, TGF is normally dominant. IGF generally increases with decreasing grain size (G, mainly at G {le} 1-10 {mu}m), increasing grain boundary phase content and the occurrence of (1) slow crack growth, (2) mist, hackle, and crack branching, and (3) (mainly finer, substantial, grain boundary) porosity, and possibly with increasing elastic anisotropy. Possible effects of grain orientation, stress rate and character, as well as microstructural stresses from thermal expansion anisotropy (TEA) are discussed. At higher temperatures, there is a general shift to more IGF, especially with more grain boundary impurities, finer G, and probably higher elastic anisotropy. This shift often starts with IGF only at the fracture origin, and may not commence until temperatures of the order of 1500 C or more in some materials. While IGF is often attributed to weaker grain boundaries (implying lower strengths), it is also often associated with fine grain size, and thus the highest strengths at lower temperatures. IGF vs TGF reflects not just grain boundary strength (as often emphasized), but a balance of this versus the fracture toughness for grain fracture (usually via cleavage, which may also entail the multiplicity of cleavage planes). Several factors may interact to shift differing balances in different materials, e.g. some increase in IGF at larger G in TiB{sub 2} with high TEA, but more IGF increase in Al{sub 2}O{sub 3}, at larger G with less TEA, and no IGF increase in BeO and all TGF in B{sub 4}C having similar TEA to Al{sub 2}O{sub 3}.

• OSTI ID: 535631
• Report Number(s): CONF-950739--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
ANISOTROPY
BERYLLIUM OXIDES
BORON CARBIDES
CERAMICS
CRACK PROPAGATION
FRACTOGRAPHY
GRAIN BOUNDARIES
GRAIN ORIENTATION
GRAIN SIZE
POROSITY
STRESSES
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
TITANIUM BORIDES