Stress dependence of dislocation networks in elevated temperature creep of a Ni-based single crystal superalloy

Abstract

The morphologies and distributions of dislocation networks in Ni-based single crystal superalloys crept at 1100 °C and a large stress range from 120 to 174 MPa were investigated. The γ/γ′ lattice misfit at 1100 °C was calculated using the Vegard's law, where the γ- and γ′-compositions were quantified by 3D Atom Probe Tomography. The results indicated that the distribution of dislocation network showed a strong stress dependence. Two parts of dislocation networks, namely close- and sparse-spaced configurations, were observed. Further, the dislocation network spacings’ analysis revealed that the close-spaced network (about 100 nm) mainly depended on the γ/γ′ lattice misfit (−0.2910 ± 0.0564)%, which was almost independent of stress. However, the sparse-spaced network (above 120 nm) might be attributed to the larger creep strain flows under higher stresses, which presented a strong stress dependence. It was demonstrated that the γ/γ′ lattice misfit played a key role in elevated temperature and low stress creep.