Environmentally-assisted grain boundary attack as a mechanism of embrittlement in a nickel-based superalloy
Research output: Contribution to journal › Article › peer-review
Colleges, School and Institutes
- University of Oxford
The loss of ductility in the high strength polycrystalline superalloy 720Li is studied in air between room temperature and 1000 °C. Tensile ductility is influenced profoundly by the environment, leading to a pronounced minimum at 750 °C. A relationship between tensile ductility and oxidation kinetics is identified. The physical factors responsible for the ductility dip are established using energy-dispersive X-ray spectroscopy, nanoscale secondary ion mass spectrometry and the analysis of electron backscatter diffraction patterns. Embrittlement results from internal intergranular oxidation along the γ-grain boundaries, and in particular, at incoherent interfaces of the primary γ′ precipitates with the matrix phase. These fail under local microstresses arising from the accumulation of dislocations during slip-assisted grain boundary sliding. Above 850 °C, ductility is restored because the accumulation of dislocations at grain boundaries is no longer prevalent.
|Number of pages||11|
|Publication status||Published - 1 Mar 2017|