The Coarsening Kinetic of γ′ Particles in Single Crystal Superalloys During Aging at High Temperatures

Turbine blades are subjected to a complex combination of elevated temperatures, high stresses and aggressive environment. With exposure to these operating conditions the service lives of the components are limited by fatigue, hot corrosion and creep. For this reason in the last years single crystal superalloys have been developed and used in aeronautic but also in land based gas turbine. In particular in this paper CMSX-4^® and SCB^® Nickel-based superalloys are analyzed. The properties of these materials are due obviously to their single crystal structure, combined with the well known strengthening effect of second phase (γ′) precipitates in the nickel matrix (γ). These precipitates increase their size during aging. In this work a comparison between the growth kinetic of γ′ precipitates of these alloys has been carried out. Samples of both materials have been aged using the same test temperatures for times up to 5000 hours and the mean particle size measured by means of image analysis. Growth kinetic laws for both alloys have been developed, but they don’t take into account rafting of γ′ particles, that has been observed to occur in the two materials in different ways. In order to better understand this aspect, creep tests with variable load have been carried out and the relative structures have been examined.