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

Abstract

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 (1 st generation), CMSX-4 (2 nd generation) and TMS-75 (3 rd 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.

Primary Crystal Orientation of the Thin-Walled Area of Single-Crystalline Turbine Blade Airfoils

“…The ultimate tensile strength UTS for TMS238 has been increased to 1348 MPa at 750 °C [1,2,3,4]. The crystal orientation, which depends on the parameters of directional crystallization and the geometry of the cast [5,6,7], have an important effect on the mechanical properties of single-crystalline superalloy casts [1,8,9], such as stress rupture life and elongation [10]. Additionally, the tensile strength and creep resistance of the blades depend on the presence of low-angle boundaries [11] and the localisation of low-angle boundaries is related to the cast geometry.…”

Variation of Crystal Orientation and Dendrite Array Generated in the Root of SX Turbine Blades

“…Some of these defects are not eliminated in subsequent stages of blades production, e.g., during heat treatment [7]. The crystal orientation, which depends on the parameters of the directional crystallization and the blades' geometry [8][9][10], has a significant effect on the mechanical properties [1,11,12], such as stress rupture life and elongation of the SX superalloy casts [13]. Additionally, the presence and localization of the low-angle boundaries (LABs) in the blades, which are related to the cast geometry, affect the tensile strength and creep resistance [14].…”