Creep-Driven Solute Segregation to Planar Faults in Ni-Base Single-Crystal Superalloys

This study proposes that creep-induced segregation to planar faults reflects the dynamic establishment of a new compositional steady state within the two-phase γ γ / γ γ ′ single-crystal Ni-base superalloy during creep. The temperature difference between the alloy’s aging condition and the creep-experiment temperature drives a creep-induced partitioning flux, causing elements to redistribute within the γ γ ′ phase and accumulate at planar faults. In this work, the single-crystal Ni-base superalloy ERBO-1 (SX) was creep-deformed using double-shear creep testing at 250 MPa and 750 °C, which is 120 °C below the preceding aging treatment temperature. At 1 and 2 pct strain, the interrupted creep states show planar faults with solute segregation as commonly observed in this low-temperature, high-stress regime. Solute segregation at superlattice extrinsic stacking faults (SESF), anti-phase boundaries (APB), and microtwins in the γ γ ′ phase reveals systematic depletion of Ni and Al, accompanied by enrichment of Re, Co, Cr, Mo, and Ti. Thermodynamic calculations predict the temperature-dependent γ γ / γ γ ′ compositions. Under the present experimental conditions, this results in increased uptake of Ni and Al and rejection of Re, Co, and Cr by the γ γ ′ phase. Consequently, depletion of Ni and Al and enrichment of Re, Co, and Cr are detected at planar defect sites. In contrast, Ti, Mo, Ta, and W segregation at microtwins and SESFs cannot be explained by bulk γ γ ′ partitioning and is instead attributed to localized phase transformations in the vicinity of the defects.