High-temperature compression testing combined with high-resolution electron backscatter diffraction (EBSD) analysis has been used to study microstructural-scale straining processes that occur during high-temperature deformation of a powder-consolidated nickel-base superalloy, Rene´88DT (GE Aviation, Evendale, OH). Orientation imaging has been employed to study grain-level straining and strain storage at temperatures between 1323 K (1050°C) and 1241 K (968°C) for strain rates between 0.1/s and 0.00032/s at nominal strain levels between 0.1 and 0.7. Two distinct deformation mechanisms were observed. At strain rates below 0.01/s, superplastic deformation dominates, while power-law creep occurs during high rate compression. Stored strain and evolution of the grain structure during deformation are dependent on strain rate during compression. At low strain rates in the superplastic regime, low levels of stored strain and some grain growth are observed. At high strain rates, dynamic recrystallization occurs along with higher levels of stored strain within selected grains, particularly those at the high end of the grain size distribution. A constitutive model for superplastic deformation was employed to predict the temperature and strain rate dependence of the transition from superplastic to power law deformation. The transition in rate sensitivity was consistent with the transition in stored strain measured by EBSD. Superplasticity-enhanced grain growth is observed and the implications for the transition in deformation mechanisms are discussed.

Microstructural-scale straining processes that occur during high temperature compression of powder-consolidated nickel-based superalloy René 88DT at 1050˚C (1925˚F) have been studied. A high temperature strain mapping technique has been utilized to quantify grain-level strain accumulation. Orientation imaging has also been employed to study grain-level straining and dislocation storage. Two distinct straining mechanisms were observed. At low strain rates grain boundary sliding dominates while intragranular plastic deformation is observed during high rate compression. Stored strain and microstructural evolution are dependent on strain rate during compression. At low strain rates superplastic deformation occurs with low levels of stored strain and some grain growth. At high strain rates dynamic recrystallization occurs along with higher levels of stored strain within selected grains, particularly those at the high end of the grain size distribution. Dynamic recrystallization results in grain refinement and flow stress softening, which all occur when misorientation within individual grains exceeds a level of approximately 5°.

No abstract