DISLOCATIONS NUCLEATION AND INTERACTION WITH GRAIN BOUNDARIES IN A POLYCRYSTALLINE NICKEL BASE SUPERALLOY

Dislocation interaction with grain boundaries is a compelling problem as it influences mechanical properties, of which tensile and fatigue behavior are the most prominent. Detailed assessment of such interactions at specific boundaries in single phase materials has led to the establishment of a slip transfer criteria. However, nickel base superalloy microstructure is more complex especially in the area surrounding of grain boundaries where, with an appropriate supersolvus heat-treatment, highly serrated boundaries develop, also exhibiting large gamma' precipitates abutting the boundary. Dislocation behavior at grain boundaries is reported in an interrupted tensile test performed at 700 degrees C in a polycrystalline nickel base superalloy exhibiting a coarse grain microstructure and a bimodal distribution of gamma' precipitates. Dislocation interaction has been assessed at three different types of boundaries: (i) a twin boundary, (ii) a highly serrated high angle grain boundary and (iii) a faceted high angle grain boundary.