Creep straining micro-mechanisms in a powder-metallurgical nickel-based superalloy

Polycrystalline NR3 nickel-based superalloy is a new-generation alloys produced by powder metallurgy for application as turbine disks of a future supersonic airplane. A special heat treatment is used to form a bimodal size distribution of γ′ precipitates. Post mortem transmission electron microscopy is used to observe dislocation structures obtained after creep around 700 °C and 650 MPa, up to 0.2% of plastic deformation. The deformation within a grain is heterogeneous and is principally due to the shearing of both types of precipitates by two different processes which where analysed. The smaller precipitates, called tertiary, are shown to play a major role in the hardening processes. In the proximity of serrated grain boundaries, where perfect dislocations are located, the deformation is higher, which is attributed to an enhanced internal stress in the middle of the grain.