ON THE MECHANISM OF SHEAR OF GAMMA' PRECIPITATES BY SINGLE (A/2)(110) DISSOCIATED MATRIX DISLOCATIONS IN NI-BASED SUPERALLOYS

The weak-beam technique of electron microscopy combined with bright-field image matching has been used to study the elementary shearing configurations of gamma' precipitates in single crystals of Ni-based superalloys after creep and dynamical experiments. The shearing configurations encountered involve superlattice intrinsic and extrinsic stacking faults and a single (a/2) <110> matrix dislocation as proposed by Condat and Decamps. The observations show changes in configuration between tension and compression that may be explained by considering the interplay between the crossing of the interface by elementary Shockley partials and the effect of the applied stress on the dissociation width of matrix dislocations. An original model for the shearing of the gamma' precipitates by a single (a/2) <110> dissociated matrix dislocation is proposed; this model is based upon the detailed mechanism of crossing of the interface by the matrix dislocation. The model provides an understanding of the dependence of the shearing processes with temperature during primary creep.