Microstructure Evolution of Single Crystal Superalloy DD6 at High Temperature

Abstract:

A low cost nickel-based superalloy DD6 has been independently developed in our country which has excellent tensile properties, high-temperature creep resistance, fatigue resistance, oxidation and corrosion resistance. DD6 superalloy has broad application prospects in fields of turbine components. In order to establish failure evaluation standard of single crystal turbine blades, heat treatments are given to DD6 in this study to simulate the actual operating temperature of turbine blades. The microstructure evolution with temperature of DD6 superalloy after heated for 50 hours is studied and analyzed. It is found that γ′ phase continuously dissolved into γ base with the increase of heating temperature. It is related to the diffusion of Al, Ti elements from γ′ phase to γ base. While DD6 are cooling from above 1150 ℃ to room temperature, the second γ′ phase particles will precipitate at wide base tunnels and grow bigger with temperature rises. The precipitation of second γ′ phase is due to composition undercooling caused by oversaturation of Al, Ti in γ base. From the point of view of thermodynamics, second γ′ phase grow to decrease interface energy. And it is related with heating temperature and cooling time from the point of view of kinetics.

Key words:Heating temperature; γ′ phase dissolving; Second γ′ phase precipitating; Elements diffusion