On the stability of orowan loops around coherent spherical ordered precipitates

The stability of a glissile loop around a coherent ordered precipitate is discussed in terms of applied stress, line tension and antiphase boundary energy. The case of a double loop is also examined. It is shown that, above a critical stress, the precipitates are sheared by the loops. This can occur for precipitate radii above the classical transition between shearing and Orowan by-passing, and is illustrated in the case of Al-Li alloys, where δ′ precipitates are by-passed by an Orowan mechanism, and then sheared by the Orowan loop.