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T. Wojcik, M. Rath, E. Kozeschnik:
"EBSD study on the recrystallization behaviour of the nickel-base superalloy Rene 65";
Talk: 19th International Microscopy Congress, Sydney, Australia; 2018-09-09 - 2018-09-14.

The recently developed Rene 65 alloy is a fine grained and γ´-strengthened Ni-base superalloy, which is intended to be used in future turbine disks applications in aero-engines. This alloy was specifically designed as a cast and wrought derivative of the powder metallurgical produced Rene 88DT alloy, with the objective to exceed the service temperature of 700°C, and therefore, to increase the efficiency of the aero-engines.
In this work, the recrystallization behaviour during thermo-mechanical processing is investigated for different temperatures and strain rates by EBSD. The γ´-precipitates have the same fcc crystal structure as the γ-matrix, with a lattice constant mismatch below 1%. Thus, these phases cannot be distinguished using EBSD patterns. Therefore, a combined EDX/EBSD acquisition is required to identify the Al- and Ti-rich γ´-precipitates within the γ-matrix phase. In contrast to deformed grains, recrystallized grains exhibit low crystal defect densities, thus low misorientations inside single grains. Therefore, the grain orientation spread function with a threshold value of 1° was used to distinguish the recrystallized grains from the not recrystallized grains, and to estimate the recrystallized fraction.
It was experimentally found that three different recrystallization mechanisms can occur in this alloy. At deformation temperatures below 1060°C, the expected discontinuous recrystallization mechanism takes place, whereas, at temperatures starting at 1060°C, a new recrystallization mechanism, supported by twinning was observed. Additionally, new recrystallized grains are formed, nucleating coherently on the surface of the primary γ´-precipitates.

EBSD precipitation gamma' superalloy recrystallization