Ultra-High Temperature Creep of Ni-Based SX Superalloys at 1250 °C

Abstract

Very high temperature creep properties of twelve different Ni-based single crystal superalloys have been investigated at 1250 °C and under different initial applied stresses. The creep strength at this temperature is mainly controlled by the remaining γ′ volume fraction. Other parameters such as the γ′ precipitate after microstructure evolution and the γ/γ′ lattice parameter mismatch seem to affect the creep strength to a lesser degree in these conditions. The Norton Law creep exponent lies in the range 6–9 for most of the alloys studied, suggesting that dislocation glide and climb are the rate limiting deformation mechanisms. Damage mechanisms in these extreme conditions comprise creep strain accumulation leading to pronounced necking and to recrystallization in the most severely deformed sections of the specimens.

Keywords

• Ni-based single crystal superalloy
• ultra-high temperature creep
• microstructure evolution
• creep damage
• γ′ volume fraction