Leap® Characterization of the γ-γ´ Interface in Crept and Annealed CMSX-4 Nickel Based Superalloy

Summary form only given. Rhenium additions have played an important role in improving the high temperature properties of nickel-based superalloys. Previous atom probe and transmission electron microscopy characterizations have demonstrated that Re strongly partitions to the γ matrix where it acts as a solid solution strengthener. Blavette et al., found evidence of 1.3 nm diameter Re clusters in classical atom probe data from the γ matrix. More recently, Re clusters containing ~10% Re were found to be located preferentially in an ~10-nm-wide Re-enriched γ region close to the γ-γ´ interface. The cuboidal L1₂-ordered primary γ´ precipitates evolve during extended creep into extended rafts perpendicular to the tensile axis. A local electrode atom probe has been used to characterize the solute distribution along and normal to the γ-γ´ interface in a crept and annealed CMSX-4 nickel based superalloy. The creep tests were performed under a tensile stress of 185 MPa at a temperature of 950°C. The tests were interrupted at times of 285, 550, 695, 1060 and 1170 h. Atom probe specimens were cut from the gauge section of the creep specimens both parallel and perpendicular to the tensile axis. Annealed specimens were also cut from the grip sections of the creep specimens. Comparison of the Al isoconcentration surfaces revealed that the γ-γ´ interface was relatively smooth for the annealed conditions but featured steps and grooves in the crept conditions. Concentration profiles constructed normal to the γ-γ´ interface from selected volumes encompassing only flat regions of the interface revealed significant solute enrichments of most alloying elements close to the interface. Ultrafine (~1 nm diameter) rhenium clusters containing up to ~10-15% Re were evident in the 10-nm wide Re-enriched region in the matrix close to the γ-γ´ inte- - rface. Re-enriched regions were also detected in asperities in the γ-γ´ interface in the crept conditions.