Intermediate temperature brittleness and directional coarsening behavior of nickel-based single-crystal superalloy DD6

The microstructure of the nickel-based single-crystal superalloy DD6 after tensile deformation has been studied by transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS). The samples were strained to fracture at room temperature, 650. °C, 850. °C and 1020. °C along the [001] orientation. The results indicate that the yield strength at 650. °C is superior to that at room temperature (20. °C), 850. °C and 1020. °C, but low ductility was observed at 650. °C. It is demonstrated that the intermediate temperature brittleness (ITB) behavior was caused by the change of the deformation mechanism at intermediate temperature. At high temperature, the γ' precipitates coarsening directionally along the direction perpendicular to the stress axis. This can be attributed to the directional diffusion of the chemical elements.