µ-Phase behavior in a cast Ni-base superalloy

The response of μ phase to applied stress and long-term thermal exposure has been investigated in the cast Ni-base superalloy K446. It is found that during stress rupture, the applied stress accelerates the precipitation and growth of μ phase. However, during thermal exposure the μ phase precipitating in the form of needles and granules experiences a complicated evolution. The needles, fiber- or sheet-shaped in three-dimension, align very regularly during exposure, either lying in three directions with an acute angle to one another or in two directions perpendicular to each other, the mechanisms of which are characterized in detail. In addition, it is concluded that an excessive precipitation of μ phase severely degrades the mechanical properties of the alloy, whereas its evolution behavior during thermal exposure is determined to have an insignificant influence on the properties.