Creep-rupture behavior of a directionally solidified nickel-base superalloy

The creep-rupture behavior of the directionally solidified (DS) nickel-base superalloy DZ17G has been investigated over a wide stress range of 60 to 950 MPa at high temperature (923 to 1323 K). In this article, the detailed creep deformation and fracture mechanisms at constant load have been studied. The results show that all creep curves exhibit a short primary and a dominant accelerated creep stage, which results in higher ductility of DS superalloy DZ17G compared to the conventionally cast alloy. From the creep parameters and transmission electron microscopy (TEM) observations, it is suggested that the dominant creep deformation mechanism has a change from gamma prime particles shearing by matrix dislocations in high stress region to dislocation climb process in low stress region. It is found that the fracture mode of DS superalloy DZ17G is transgranular, and it is controlled by the propagation rate of deep cracks initiated at both surface and inner microstructure discontinuities. The creep rupture data follows the Monkman-Grant relationship under all the explored test conditions.