Creep crack behaviour of a coarse grain nickel-base super alloy

The paper presents creep crack growth data, obtained for cast nickel-base super alloy IN-738 LC, which represents a typical large coarse grain structure. Long term creep crack growth experiments were performed at 700 and 850 degrees C on side-grooved compact tension and corner crack specimens. In parallel, uniaxial creep tests on smooth specimens were conducted. The coarse grain structure has been examined using electron backscatter diffraction (EBSD). Creep fracture in polycrystalline materials is observed to be typically intergranular and dominates along grain boundaries. These observations were confirmed for the investigated alloy. From metallographic examinations, an effect of grain orientation on creep crack behaviour, however, was not observed. The Nikbin-Smith-Webster (NSW) model, which is based on the creep fracture mechanics parameter C*, and a damage accumulation model, which considers only nominal stress in the ligament, lead to reasonable results when recalculating creep crack growth.