Normal and Abnormal Grain Growth in Ceramics - NbC-Co and Alumina |
| Journal |
Advanced Materials Research (Volumes 11 - 12) |
| Volume |
AICAM 2005 |
| Edited by |
Masayuki Nogami, Riguang Jin, Toshihiro Kasuga and Wantai Yang |
| Pages |
47-52 |
| DOI |
10.4028/www.scientific.net/AMR.11-12.47 |
| Online since |
February, 2006 |
| Authors |
Jong Hoon Lee,
Min Cheol Chu,
Seong Jai Cho,
Duk Yong Yoon
|
| Keywords |
70NbC-30Co, Abnormal Grain Growth, Aluminum, Grain Shape, Interface Roughening |
| Abstract |
Normal and abnormal grain growth has been observed in 70NbC-30Co with varying B
concentrations at 1450°C and in alumina with varying impurity and additive concentrations at 1600°C
-1650°C as typical systems with and without liquid matrix. The grain growth behavior depends on the
roughening of the interfaces as indicated by the grain and grain boundary shapes. When 4% B is added
to 70NbC-30Co, the NbC grains in Co-rich liquid matrix are spherical and undergo diffusion
controlled normal growth, because the grain-liquid interface is rough. As the B concentration is
decreased to 3, 2, 1, and 0%, the NbC grains become more cubic and the tendency for abnormal grain
growth increases because of the step growth mechanism of the flat singular surface segments. When
compacts of high purity alumina powder are sintered at 1650°C, the grain boundaries are smoothly
curved, indicating their atomically rough structures. With increasing impurity content—in particular
SiO2—in the alumina powder, abnormal grain growth becomes more pronounced with increasing
number of flat grain boundaries. These singular grain boundaries are expected to move by a step
mechanism and thus cause the abnormal grain growth. These results show that the interface
roughening and hence the grain growth mode changes gradually with the additive or impurity
concentrations. Therefore, the abnormal grain growth cannot be sharply distinguished from the
normal grain growth as has been previously suggested in general and for alumina in particular. |
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