Phase Transformation on Chemically Corroded Surface of a Single-Crystal Superalloy During In-Situ Tension at Elevated Temperatures

Abstract:

In-situ tensile tests were conducted on a chemically corroded third-generation single-crystal superalloy DD9 at 980 and 1100 ℃. The phase transformation in the surface areas during the tensile process was analyzed using field emission scanning electron microscope, energy dispersive X-ray spectroscope, electron probe X-ray microanalysis, and transmission electron microscope. The phase transformation mechanism on the surface and the influence mechanism were studied through observation and dynamic calculation. During tensile tests at elevated temperatures, chemical corrosion promotes the precipitation of topologically close-packed (tcp) μ phase and σ phase on the alloy surface. Both the precipitation amount and size of these two phases on the surface at 1100 ℃ are greater than those at 980 ℃. The precipitation of tcp phase on the alloy surface results in the formation of an influence layer on the surface area, and the distribution characteristics of alloying elements are significantly different from those of the substrate. The depth of the influence layer at 1100 ℃ is greater than that at 980 ℃. The precipitation of tcp phase prompts the phase transition from γ phase to γ′ phase around the tcp phase.