Page 98 - Materials Chemistry, Second Edition

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2.3. The Crystalline State

Figure 2.54. Illustration of a true stress vs. strain curve and comparison of stress–strain curves for various
materials. UTS ¼ ultimate strength, and YS ¼ yield strength. The tensile strength is the point of rupture,
and the offset strain is typically 0.2% – used to determine the yield strength for metals without a well-
[48]
defined yield point. Reproduced with permission from Cardarelli, F. Materials Handbook, 2nd ed.,
Springer: New York, 2008. Copyright 2008 Springer Science & Business Media.

In single crystals, there are preferred planes where dislocations may propagate,
referred to as slip planes. For a particular crystal system, the planes with the greatest
atomic density will exhibit the most pronounced slip. For example, slip planes for
bcc and fcc crystals are {110} and {111}, respectively; other planes, along with
those present in hcp crystals, are listed in Table 2.9. Metals with bcc or fcc lattices
have significantly larger numbers of slip systems (planes/directions) relative to hcp.
For example, fcc metals have 12 slip systems: four unique {111} planes, each