The effect of thickness on the creep properties of a single-crystal nickel-based superalloy

Creep rupture tests were conducted at 980 degrees C/250 MPa on specimens with different wall thickness values obtained from a single-crystal nickel-based superalloy. Experimental results showed that the thin specimens had an inferior creep life compared with the thick ones. All specimens were oxidised during the creep tests. Electron probe microanalysis and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed that internal nitrides developed in the y'-free zone and even in the matrix. The presence of internal nitrides induced the nucleation of creep voids and initiation of cracks during creep rupture, thereby increasing the growth rate of cracks and facilitating the failure of the creep specimens. The morphology of the fracture sections indicated that the interaction of cracks and creep damage also contributed to this phenomenon. Cracks played an important role in the creep behaviour of the thin specimens, and creep damage effectively influenced that of the thick specimens.