Influence of Crystallographic Orientation on Creep Behavior of Aluminized Ni-Base Single Crystal Superalloys

The effect of chemical compositions and secondary crystallographic orientation dependence on the formation of diffusion layer and creep behavior were investigated. Three alloys of different generations: PWA 1480 (1st generation), CMSX-4 (2nd generation) and TMS-75 (3rd generation), were studied. After aluminized coating process, creep rupture test were performed at 900 °C and 392 MPa. The creep rupture properties of the alloys with and without the aluminized coating treatment were compared. The coating treatment resulted in a significant decrease in rupture lives for three alloys. No reductions in rupture elongation were observed. Creep strength was significantly degraded with aluminide coating due to the diffusion layers formed under coating layer. Creep fractures of the coated materials were essentially controlled by the crack nuclei in the coated layer. It was also found that the specimens with (100) side-surface showed longer creep rupture life than the specimens with (110) sidesurface, which means the results were anisotropic with respect to the secondary orientation which is normal to the primary orientation. The anisotropic creep behavior was caused by the different arrangement of {111}<101> slip systems between the two side-surface specimens. The results obtained in this study suggest the importance of secondary orientation normal to the component surface on designing the single-crystalline turbine blades.