On the phase stability of MARM247LC alloy during long term thermal exposure

The microstructures stability of directional-solidified (DS) MarM247LC alloy were investigated during thermal exposure at 800–950 °C up to 5000 h. In the dendrite core (DC), the particle size distribution (PSD) of γ′ phase shows that the coarsening mechanism is consistent with the trans-interface diffusion-controlled coarsening (TIDC) theory. While at the second dendrite arms (SDA), the γ′ phase gradually undergoes directional coarsening, with the coarsening direction perpendicular to the SDA growth direction. Besides, when the temperature increases to 900 °C, the effective diffusion coefficient and the lattice misfit of γ/γ′ lead to a significant increase in the coarsening rate of the γ′ phase. At the same time, the M6C carbides precipitated a lot in the DC enriching with W element and its distribution gradually changed to a cross-like distribution due to the formation of misfit dislocations of γ matrix. And the{200} plane is the coherent interface of M6C and γ matrix.