Effects of Dendritic Orientation on Stress Rupture Properties of DD6 Single Crystal Superalloy

Abstract

DD6 single crystal superalloy slabs were prepared with seed method in the directionally solidified furnace with high temperature gradient. The transverse stress rupture properties and fracture behaviour of the alloy at 760 °C/758 MPa, 850 °C/550 MPa and 980 °C/250 MPa were investigated and compared with those of longitudinal specimens. The transverse stress rupture lives are corresponding with the longitudinal stress rupture lives at 760 °C/758 MPa and 850 °C/550 MPa. The transverse stress rupture lives are slightly less than the longitudinal stress rupture lives at 980 °C/250 MPa. The fracture mechanism of the transverse stress rupture of the alloy at 760 °C/758 MPa shows quasi-cleav-age mode and the fracture mechanism at 980 °C/250 MPa shows dimple mode, while the fracture mechanism at 850 °C/550 MPa shows quasi-cleavage and dimple mixture mode. At higher temperature and lower stress, the microcracks are easier to initiate and interconnect in the transverse specimen than those in longitudinal specimen because there are interdendritic regions perpendicular to the axis of stress.