Influence of microstructure stability on creep properties of single crystal nickel base superalloys

The influence of microstructure stability on the creep properties of single crystal nickel-based superalloys was investigated by means of the measurement of the creep curves and microstructure observation. Results show that the superalloy with 4%(mass fraction)W in Ni-Al-Cr-Ta-Co-5.5%Mo-x%W systems displays a better microstructure stability, but the P phase is precipitated in the superalloy with 6% W during aging. The strip-like mu phase is precipitated to be parallel or perpendicular to each other along the < 110 > orientation, and grown into the slice-like morphology along the {111} planes. The superalloy with 4%W displays a better creep rupture lifetime under the applied stress of 200 MPa at 982 degrees C, but the creep lifetime of alloy is obviously decreased with the increase of the element W content up to 6%. The fact that the mu phase is precipitated in the superalloy with 6% W during applied stress and unstress aging results in the appearance of the poor regions for the refractory elements. This is one of the main reasons for reducing the creep rupture lifetime of the superalloy.