Effect of wall thickness on micropores and stress-rupture properties of a single-crystal nickel-based superalloy

The effect of wall thickness on the microporosity and stress-rupture properties of a second-generation single-crystal nickel-based superalloy was investigated using optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray computed tomography. Specimens with various thicknesses (0.8, 1, 1.5, and 3 mm) were subjected to stress-rupture experiments at 980 °C and 250 MPa. The stress-rupture lives of the 0.8- and 1-mm-thick samples were shorter than those of the 1.5- and 3-mm-thick samples. The results indicate that increasing wall thickness results in an increased eutectic fraction, primary dendrite arm spacing, and degree of dendritic segregation of the as-cast alloys, which promotes porosity growth during solution heat treatment. The reduction in the real load-bearing cross-sections and a discontinuous Al2O3 layer caused by the oxidation behavior significantly influence the fracture mechanism of the thin-walled specimens, whereas preexisting micropores significantly affect the stress-rupture properties of the thicker specimens.