Acceleration Mechanism of Intergranular Cracking of Ni-Base Superalloy GH4169 under Creep Loading at Elevated Temperatures due to the Growth of δ-Phase

Abstract

In order to quantitatively clarify the effect of δ-phase precipitation on the strength of grain boundary in Ni-based superalloy GH4169 at elevated temperatures, which is expected to be used in aircraft engines, intermittent creep tests at 800°C were conducted on specimens, and the microstructural changes were analyzed using EBSD analysis. The effects of δ-phase precipitation and creep damage were evaluated by micro tensile tests. It was confirmed that there is a large lattice mismatch between the δ-phase precipitated around the grain boundary and the matrix phase, and that dislocations and voids accumulate in the grain boundary. It was also suggested that the δ phase precipitation may be a stress-induced diffusion phenomenon. Furthermore, it was confirmed that the strength of this alloy decreased in the early period of creep, influenced by both creep damage and the precipitation of δ-phase.