Abstract
The creep resistance of single-crystalline Ni-base superalloys at elevated temperatures depends among others on solid solution strengthening of the γ-matrix. To study the influence of various solid solution strengtheners on the mechanical properties, a series of Ni-base superalloys with the same content of different alloying elements (Ir, Mo, Re, Rh, Ru, W) or element combinations (MoW, ReMo, ReW) was investigated. Nanoindentation measurements were performed to correlate the partitioning behavior of the solid solution strengtheners with the hardness of the individual phases. The lowest γ′/γ-hardness ratio was observed for the Re-containing alloy with the strongest partitioning of Re to the γ-matrix. As a result of the creep experiments in the high-temperature/low-stress regime (1373 K (1100 °C)/140 MPa), it can be concluded that solid solution hardening in the γ-phase plays an essential role. The stronger the partitioning to the γ-phase and the lower the interdiffusion coefficient of the alloying element, the better the creep resistance. Therefore, the best creep behavior is found for alloys containing high contents of slow-diffusing elements that partition preferably to the γ-phase, particularly Re followed by W and Mo.
Highlights
MODERN nickel-base superalloys contain many alloying elements to improve the mechanical properties and to increase the operating temperatures for higher efficiency
The creep behavior of superalloys is a key factor regarding the lifetime of a turbine blade
The partitioning behavior of the alloying elements in Ni-base superalloys is of major interest for their application in high-temperature environments
Summary
MODERN nickel-base superalloys contain many alloying elements to improve the mechanical properties and to increase the operating temperatures for higher efficiency. Their microstructure consists of c¢-precipitates (L12-structure), which are coherently embedded in a soft c-matrix (A1-structure). The creep behavior of superalloys is a key factor regarding the lifetime of a turbine blade. In addition to the microstructural characteristics like the c¢-volume fraction, c¢-size and c¢-morphology, the mechanical properties mostly depend on the solid solution hardening of the c-phase, especially in the high-temperature/low-stress regime
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