The formation of precipitate free zones along grain boundaries in a superalloy and the ensuing effects on its plastic deformation

Abstract The growth of γ ′ -precipitate free zones (PFZs) along grain boundaries in polycrystals of the γ ′ -strengthened nickel-based superalloy NIMONIC PE16 and the ensuing effects on the yield strength, the ultimate tensile strength, and the plastic strain to fracture have been experimentally investigated. If the width of PFZs exceeds a well-defined limit, they lower the yield strength drastically. This result is interpreted on the basis of in situ transmission electron microscopic observations of the dislocation processes operating in the PFZs: the ease with which dislocations are generated in the PFZ and the resulting dislocation pile-ups lead to the reduction of the yield strength. Experimental observations of possible effects of PFZs on the appearance of the stress versus strain-curves and/or on the fracture mode were inconclusive: the observed effects may as well have been caused by the carbide particles formed at the grain boundaries.