Microstructural Characterization and Mechanical Properties of Rene 65 Precipitates

Nickel based superalloys are used in the aerospace industry as turbine rotor material due to their high strength and excellent fatigue resistance at high temperature. High strength is required for the high stress and high temperature environments in which these alloys operate. This is achieved by their microstructure of gamma matrix/gamma prime precipitates. The latter can cause thermomechanical processing issues since they can make the material extremely hard. The purpose of this work is to characterize the gamma prime precipitates which are present in Rene 65, a newly developed cast and wrought nickel-based superalloy by General Electric and ATI. The main precipitate that was examined was the gamma prime phase [Ni3 (Al, Ti)], which largely determines the mechanical properties of the alloy. The gamma prime in this particular alloy was found to form in three different sizes; primary, secondary and tertiary. After various heat treatments, the differences in the volume fraction and morphology of each precipitate type is described and the effect of the precipitates on hardness is determined.