Improvement of stress–rupture property by Cr addition in Ni-based single crystal superalloys

The effects of Cr addition on the microstructure and stress–rupture property have been investigated in three experimental Ni-based single crystal superalloys containing various levels of Cr addition (0–5.7 wt.%). The Re partitioning ratio increased and the lattice misfit became more negative with increasing the Cr addition in both dendrite core and interdendritic region. The changes of elemental partitioning behaviors and the lattice misfit show good agreement with the change of γ′ morphology. Cr addition increased the stress–rupture life at 1100 °C/140 MPa significantly due to higher γ′ volume fraction, more negative lattice misfit and a well rafting structure as well as less width of γ channels. High Cr addition (5.7 wt.%) increased the degree of Re and Cr supersaturation in the γ phase and promoted the formation of topologically close-packed (TCP) phases significantly under thermal exposure and creep deformation at 1100 °C.

Research highlights
► Cr improved the stress–rupture life of single crystal superalloys significantly.
► Cr increased the Re partitioning ratio and resulted in more negative misfit.
► Mechanism for improving the stress–rupture life by Cr addition is addressed here.