Improvement of Creep Resistance at 950 degrees C and 400 MPa in Ru-Containing Single-Crystal Superalloys with a High Level of Co Addition

摘要

Microstructural features, including gamma' volume fraction and size, gamma-gamma' lattice misfit, gamma channel width, and dislocation substructure, are known to significantly influence the creep performance in Ni-base single-crystal superalloys. In this study, the microstructural characteristics of Ru-containing single-crystal superalloys with different levels of Co, Mo, and Ru additions were quantitatively investigated after ruptured and interrupted creep tests conducted at 1223 K (950 degrees C) and 400 MPa. The creep lifetime was slightly increased with the high level of Co addition and significantly increased with the coadditions of Mo and Ru. A minor effect of Co content on the gamma channel width and gamma' volume fraction was found in experimental alloys. The alloy with high levels of Mo and Ru additions was determined to possess a more negative gamma-gamma' lattice misfit, and a high density of stacking faults (SFs) was formed in the gamma channels during creep. The combined effects of the SFs in the gamma matrix serving as the barriers to dislocation movement, as well as the dense interfacial dislocation networks preventing dislocation to shear the gamma' phase, were considered as the main mechanism responsible for the improvement of creep resistance. Results from this study are helpful to understand the effect of microstructural features on creep performance and contribute to the knowledge of physical metallurgy in Ru-containing single-crystal superalloys. (C) The Minerals, Metals & Materials Society and ASM International 2018