Influence of primary and secondary orientations on creep rupture behavior of aluminized single crystal Ni-based superalloy

Influence of primary and secondary orientations on the creep behavior of aluminized single crystal Ni-based superalloy was investigated at a high temperature with various tensile stress directions and side-surface orientations. The specimens were aluminized by pack aluminizing treatment at 1000 °C for 5 h under argon flow. The creep rupture tests were performed at 900 °C/392 MPa for thick specimens and at 900 °C/300 MPa for the thin specimens. The aluminizing treatment reduced the creep strength of the superalloy because of the crack initiation in hardened diffusion layers. Furthermore, it was found that the creep strength of thin aluminized specimens was affected by the crystallographic orientations, not only in the tensile direction, but also in the thickness direction. This is due to the difference in the crystallographic geometry of {111} planes, which is associated with the magnitude of 〈112〉 direction shear stress on the planes and the effective cross-section change by the crack propagation.