Kink Mechanism for Deformation

The high strength of most ceramics is due to the difficulty of moving dislocations through the lattice that is, most ceramics have a high Peierls stress. Dislocations move from one Peierls valley to the next by the nucleation of a kink pair, under the action of applied stress and temperature. The kinks are abrupt and their further motion is controlled by a secondary Peierls barrier. Mitchell, Peralta and Hirth [22] have adapted the standard treatment of Hirth and Lothe [23] to show that the resulting strain-rate is given by  

Because stress and temperature occur in several places inside and outside the exponents, Eq. (1) must be solved numerically. The activation energy, Q= 2Fh- -Qp, can be determined approximately from the slope of an Arrhenius plot or the slope of a plot of log a against T. However, the apparent activation energy determined in this 

The relative contributions of the kink formation energy (2Fk) and the kink diffiision energy (Qd) are unknown. However, should be of the form a (ib h, where a is a constant of the order 0.1 for an abrupt kink (a kink with a width of atomic dimensions), and an order of magnitude smaller for a relaxed kink (a kink with a width much greater than atomic dimensions) [23], so that  

Modification of the Model for Kink Pair Nucleation on Point Delects, and Partial 

In Mg0 nAl203 (n 1), the CRSS decreases dramatically with increasing deviation from stoichiometry that is, with increasing n. In fact, the CRSS was found [26] to be proportional to [VJ, where [VJ is the concentration of charge-compensating cation vacancies which is related to n by 

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