EFFECTS OF Cr ON THE STRESS RUPTURE OF Ni-BASED SINGLE CRYSTAL SUPERALLOYS

Effects of different levels of Cr-additions (0 similar to 5.7 wt.%) on the morphology of gamma' precipitates, microstructural stability, stress-rupture property and post-stress-rupture microstructures were investigated in the current study. The results indicate that the morphology of gamma' precipitates was nearly spherical in the Cr-free alloy and it changed to be more cuboidal with increasing levels of Cr additions. In the meantime, the volume fraction of gamma' precipitates increased while the precipitate size decreased with the increasing level of Cr content. High level of Cr addition (5.7 wt.%) promoted the formation of TCP phase significantly at 1100 degrees C, which was enriched in Re, W and Cr. Meanwhile, the stress-rupture life of the investigated alloys increased with increasing Cr content. High level of Cr addition promoted the stress-rupture life significantly even though the existence of TCP phases. The stress-rupture life of the alloy containing 5.7 wt.% Cr was 4.7 times that of Cr-free alloy at 1100 degrees C/140 MPa. It is suggested that Cr additions changed the partitioning behaviors of alloying elements in gamma and gamma' phases significantly, which in turn resulted in more cuboidal gamma' precipitates, more negative lattice misfit and the corresponding better stress-rupture property with the increasing Cr content.