Negative influence of rafted gamma ' phases on 750 degrees C/750 MPa creep in a Ni-based single crystal superalloy with 4% Re addition

摘要

Specimens with two different gamma' phase microstructures, named as-heat treated sample with cuboidal gamma' phases and pre-rafted sample with N-type rafted gamma' phases, were compared to investigate the negative influence of the rafted gamma' phases on the creep property in a Ni-based single crystal superalloy with 4% Re addition at 750 degrees C and 750 MPa condition. The results indicated that the sample with cuboidal gamma' phases exhibited a lower creep rate and a longer rupture life compared to that with rafted gamma' phases. Transmission electron microscope examinations showed that lots of fine gamma' phases impeded first the dislocation movement in the channel of gamma matrix in the initial primary creep stage before the cuboidal gamma' phases were cut by stacking faults in as-heat treated sample. However, in pre-rafted sample, some existed superdislocations located in rafted gamma' phases and the mismatch stress release at gamma/rafted gamma' interface resulting from pre-rafted treatment not only decreased the creep resistance of rafted gamma' phases, but also weakened the gamma/rafted gamma' interface pinning effect for dislocation movement. Therefore, the rafted gamma' phases were easily cut by superdislocations and stacking faults resulting in a higher creep rate and a shorter creep life.