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8.3 - Hence coarse grain materials are preferred for...

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Since ceramics are used in high-temperature applications, it is important to consider their creep characteristics. Diffusion is more complicated in ceramics and so the dominant mechanism of creep is the sliding of adjacent grains along their grain boundaries. Some impure refractory ceramics have a glassy phase at the grain boundaries, and so the mechanism of sliding there is due to viscous deformation of this glass phase. In either case, the easy sliding mechanism at the grain boundaries is generally undesirable due to the resulting weakness at high temperatures.
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Unformatted text preview: Hence coarse grain materials are preferred for applications at high temperatures. ♦ Creep can be operative at low temps if the material has relatively low melting points. Hence creep can occur in poymers at room temperature. ♦ Stainless steels and refractory metals are especially good for creep resistance. ♦ Factors that give materials good creep resistance: 1. high melting temperature 2. high elastic modulus 3. less grain boundaries...
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