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Creep
· When materials are used at a high temperature,
the thermodynamically favored point defects in their structures are highly
mobile. This must be taken into account when designing high temperature
structures.
· In the absence of concentration
gradients, there will be no preferred direction of motion for these
diffusing atoms as the potential barriers to their motion are symmetrical.
· In the presence of an applied stress
the Gibbs function of the structure is position dependent and this stress
effect is superimposed on that due to the lattice periodicity as shown opposite.
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