CREEP DEFORMATION AND CRACK-GROWTH BEHAVIOR OF A SINGLE-CRYSTAL NICKEL-BASE SUPERALLOY

Uniaxial creep deformation and crack growth data are presented on the single-crystal nickel-base superalloy SC16, which is a candidate mater ial for industrial gas turbine applications. All testing was performed at 900 degrees C, The uniaxial experiments were conducted with the lo ading direction aligned approximately along the [001] crystallographic axis of the material. Under these conditions, a small primary region followed by mainly tertiary creep was obtained, and failure initiated from cracks at interdendritic pores. The crack growth experiments were performed on single-edge notch tension specimens and compact tension test pieces containing deep side grooves to examine state-of-stress ef fects. A selection of crystallographic orientations was also examined. Little effect of stress state and orientation was obtained. It has be en found that the creep crack growth characteristics of the alloy can be predicted satisfactorily from a model of the accumulation of damage at a crack tip using the creep fracture mechanics parameter CY and as suming plane stress conditions.