Dynamics of micromechanisms controlling the mechanical behaviour of industrial single crystal superalloys

When deforming bulk material, micromechanisms involving moving defects result in mechanical characteristics observed at a macroscopic scale.In situ straining of microsamples in a Transmission Electron Microscope, provides the unique advantage of observing the dislocation dynamics involved in such micro-deformation processes under the combined effects of stress and temperature. Here the efficiency of this technique is illustrated by describing the different obstacles controlling the movement of dislocations in a two-phase industrial single crystal superalloy. At 25‡ and 850‡C, different core structures of the moving dislocations as well as several ways of crossing obstacles are described, which concern the movement of dislocations inγ channels, at γ/γ′ interfaces and while shearing γ′ precipitates. From these observations, a quantitative analysis is developed leading to the evaluation of the critical propagation stresses involved in the channels of the matrix and when crossing the interfaces. This allows to discuss the various sites of resistance opposed to the dislocation movements and controlling the macroscopic deformation.