Research On The Precipitation And Coarsening Behavior Of γ″ Phase In Alloy GH4169

Superalloy refers to the metallic material capable of resisting strong stress at high temperatures(above 600 ℃). As one of the most widely used superalloys,Ni-based GH4169 plays a significant role in fabricating engine blades, turbine engine,and the compressor set. GH4169 alloy exhibits a good combination between strength and ductility, favorable corrosion resistance, and superior weld ability, which is closely related to the precipitates. Generally, it is suggested that the precipitates in alloy GH4169 include γ′ phase, δ phase, γ″ phase and small amount of Nb(N)C. γ″phase, the primary strengthening phase, makes a dominated contribution on the mechanical performances of GH4169 at high temperature. Meanwhile, the maximum use temperature of GH4169 is limited by the thermal stability of γ″ phase too.Therefore, it is essential to investigate the precipitation behavior of γ″ phase in GH4169 alloy and the evolution of γ″ phase at high temperatures.In this work, by heating the GH4169 alloy to various temperatures for different times, the precipitation and coarsening behaviors of γ″ phase in GH4169 are explored through differential thermal analysis(DTA), microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The conclusions can be summarized as follows:(1) During the cooling from solution temperature to room temperature, the precipitation of γ″ phase can be significantly affected by the cooling rate. Under high cooling rate, the γ″ phase tends to precipitate at a lower temperature.(2) The precipitation temperature of γ″ phase can also be affected by the Nb content in matrix. The reduction of Nb will retard the precipitation of γ″ phase.(3) In the coarsening of γ″ phase, the morphology of γ″ phase varies from lip-shape to disc-shape, and ultimately to irregular rectangle-shape, which is relevant to the size of γ″ phase.(4) The coarsening behavior of γ″ phase follows the kinetic predictions of the Lifshitz–Slyozov–Wagner(LSW) theory with a volume diffusion-controlled growth.The cubed size of the major axis of γ″ phase linearly depends on the time. In the case where γ″ phase is coherent with the matrix, the diffusion activation energy is determined as 298 k J mol-1. While the diffusion activation energy will be reduced to289 kJ mol-1as the γ″ phase loses the coherent relationship with the matrix.