TABLE OF CONTENTS The mechanical properties of ceramic materials are strongly influenced by the strong interatomic bonds that prevail. Dislocation mechanisms, which create slip mechanisms in softer metals, are relatively scarce in ceramics, and failure may occur with very little plastic deformation (the small elongation that occurs before failure). Ceramics also tend to fracture with little resistance. They have a very high melting point, as shown in Table 8.2.
| Material | Melting point ( C) |
|---|---|
| SiC | 2700 |
| BN | 2732 |
| AlN | 2232 |
| BEO | 2570 |
| Al 2O 3 | 2000 |
The temperature coefficient of expansion (TCE) phenomenon has serious implications in the applications of ceramic substrates. When a sample of material has one end fixed, which may be considered to be a result of bonding to another material that has a much smaller TCE, the net elongation of the hotter end per unit length, or strain ( E), of the material is calculated by
| (8.4) |  |
where E = strain in length/length
? T = temperature differential across the sample
Elongation develops a stress ( S) per unit length in the sample as given by Hooke s law.
| (8.5) |  |
where S = stress in psi/in (N/m 2/m)
Y = modulus of elasticity in lb/in 2 (N/m 2)
When the total stress (as calculated by multiplying the...
