Abstract
The creep responses of the superalloy CMSX-4 under thermal cycling conditions (900 °C to 1050 °C) and constant load ( sigma_{0} = 200 MPa ) were analyzed using TEM dislocation analysis and compared to the modeled evolution of key creep parameters. By studying tests interrupted at different stages of creep, it is argued that the thermal cycling creep rate under these conditions depends on the creation of interfacial dislocation networks and their disintegration by the γ′-shear of dissimilar Burgers vector pairs.
Highlights
SINGLE-CRYSTAL nickel-based superalloys are primarily used as turbine blade materials for aeronautical and power generation applications due to their unique resistance under high-temperature creep conditions
The association of the minimum creep rate with the completion of effective interfacial networks protecting against c¢-shear further helps to explain why the creep minimum is reached for all test conditions at roughly the same amount of accumulated creep strain, when the longest cycle (27:3) is the slowest to form well-developed c¢-rafts with the least time spent in the c¢-rafting regime
The cyclic creep response for a tertiary-creep regime dominated base condition, cycling into the c¢-rafting regime was analyzed. Under these conditions the creep strain rate, the onset of c¢-rafting and the formation of interfacial networks is considerably faster than isothermal testing at base temperature
Summary
SINGLE-CRYSTAL nickel-based superalloys are primarily used as turbine blade materials for aeronautical and power generation applications due to their unique resistance under high-temperature creep conditions. In combination with their preferential casting direction and the absence of grain boundaries, the creep life is enhanced due to a bi-phasic microstructure of harder c¢-precipitates (in an Ni3Al L12-ordered arrangement) coherently embedded in a softer c-matrix (disordered fcc).
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