The locking of 〈112〉/3 super-Shockley partials in L1₂ ordered γ′ single crystals deformed at 77K

Abstract

Abstract

The structure of dislocations in L1₂ ordered γ′ single crystals (Ni₃Ga and Ni₃Al) deformed at 77 K has been studied by high resolution transmission electron microscopes. 〈110〉 superdislocations have been observed to dissociate into 〈112〉/3 super-Shockley partials coupled by superlattice intrinsic stacking faults (SISF). The substructure is characterized predominantly by SISF ribbons and the SISF ribbons are enclosed by 〈112〉/3 super-Shockley partial loops which have been identified to be the trailing super-Shockley partial on expanding superdislocations. Most of the 〈112〉/3 super-Shockleys are lying along 30-degree 〈110〉 directions. The low mobility of 30-degree 〈112〉/3 partials has been interpreted as their having transformed into the non-planar structure of Giamei locks. The core structure of 30-degree 〈112〉/3 super-Shockleys has been observed with lattice imaging TEM and the results are consistent with the Giamei lock. The effect of the locking of 30-degree 〈112〉/3 super-Shockleys on the motion of dislocations is discussed.