ISSN:
1662-8985
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Normal and abnormal grain growth has been observed in 70NbC-30Co with varying Bconcentrations 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 theroughening of the interfaces as indicated by the grain and grain boundary shapes. When 4% B is addedto 70NbC-30Co, the NbC grains in Co-rich liquid matrix are spherical and undergo diffusioncontrolled normal growth, because the grain-liquid interface is rough. As the B concentration isdecreased to 3, 2, 1, and 0%, the NbC grains become more cubic and the tendency for abnormal graingrowth increases because of the step growth mechanism of the flat singular surface segments. Whencompacts of high purity alumina powder are sintered at 1650°C, the grain boundaries are smoothlycurved, indicating their atomically rough structures. With increasing impurity content—in particularSiO2—in the alumina powder, abnormal grain growth becomes more pronounced with increasingnumber of flat grain boundaries. These singular grain boundaries are expected to move by a stepmechanism and thus cause the abnormal grain growth. These results show that the interfaceroughening and hence the grain growth mode changes gradually with the additive or impurityconcentrations. Therefore, the abnormal grain growth cannot be sharply distinguished from thenormal grain growth as has been previously suggested in general and for alumina in particular
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/39/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.11-12.47.pdf
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