Study on Influence and Mechanisms of Mixed-Grain Structures on the Rupture Creep Properties of Nickel-Based Wrought Superalloys

Abstract:

Through controlling forging and heat treatment processes of nickel-based wrought superalloy, the microstructures with coarse grain volume fractions ranging continuously from 0% to 100% were prepared, and the stress rupture properties of different mixed-grain structures were tested under the condition of 730 ℃/530 MPa to explore the influence regularity and mechanism of mixed-grain structures on the stress rupture properties. The research results show that the mixed-grain structures with coarse grain volume fractions from 0% to 100% exhibit significantly different stress rupture properties. The mixed-grains structure with coarse grain volume fraction of 15% presents the shortest stress rupture life, while the coarse-grained structure with coarse grain volume fraction of 100% possesses the longest stress rupture life. The high-temperature stress rupture fracture surfaces of the mixed-grain structure specimens with low coarse grain volume fraction from 0% to 15% show typical ductile fracture characteristics, whereas those of the specimens with high coarse grain volume fraction from 50% to 100% present intergranular fracture characteristics. The high-temperature stress rupture deformation mechanisms of all mixed-grain structure specimens take the form of intragranular deformation governed by dislocation motion and grain boundary sliding. However, with the increase in coarse grain volume fraction, the high-temperature stress rupture properties of the superalloy are improved as the strong textures on the {111} crystal planes is changed, the internal dislocation distribution in coarse and fine grains is inhomogeneous, and the tendencies of stress concentration and cavity nucleation induced by dislocation pile-up and grain boundary sliding are significantly changed.