Consequences of a Room-Temperature Plastic Deformation During Processing on Creep Durability of a Ni-Based SX Superalloy
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Ni-based single crystalline superalloys are used for high-pressure parts of aero-engines due to their superior mechanical properties and very good oxidation resistance at high temperature. However, shocks or unexpected mismatch in thermal contraction between molds and castings can occur during casting process and subsequent heat treatments, inducing plastic deformation of the alloy at low temperature. To mimic such events, a tensile plastic deformation is applied at room temperature on solutioned AM1 specimens and followed by standard aging heat treatments. Faster growth of the γ′ precipitates inside plastically deformed bands is obtained after full heat treatment with no lattice rotation or recrystallization. It has however been evidenced that the applied deformation has a detrimental impact on the creep properties, especially at high temperature (above 950 °C). It partly results from a highly localized failure process along former slip bands in which recrystallization is observed. The evolution of the microstructure during creep tests of prior deformed and nondeformed specimens has been thoroughly investigated to better identify under which conditions recrystallization occurs inside the bands during a creep test and by which mechanism.
The authors are grateful to Professor Dierk Raabe and Dr. Baptiste Gault (both from Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany) for the interpretation of APT results and fruitful scientific discussions. The authors thank Dr. Susanne Steuer, formerly at the Institut Pprime and UCSB and now at Thyssenkrupp for technical assistance on creep testing. The authors also gratefully acknowledge the fruitful scientific discussions on recrystallization with Dr. Nicolas Leriche (from Safran Aircraft Engines, Gennevilliers, France).
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