Diffusion plays the most basic role in determining a variety of structural features in nickel-based single crystal superalloys (Ni-SXs). The interaction of solutes and vacancies towards the chemical gradient affects different microstructure evolution processes such as phases precipitation and γ′ coarsening [1, 2]. On a larger scale, the long-range diffusion towards concentration gradient drives homogenization on dendritic structures during heat treatments [3].

Dendritic segregation is very familiar phenomenon in high generation Ni-SXs alloying with increased refractory elements. Recently, we occasionally found the segregations are gradually increased during 1100℃/137MPa creep tests (see Fig. 1a). This phenomenon is related to the dislocation pipe diffusion theory in Ni-SXs which suggests the interaction of alloying solutes with dislocation motion plays the key role in affecting local chemical distribution [4, 5]. Based on series of TEM observations and studying of dislocation substructures, we have proved the movements between dendritic and interdendritic region drives the long-range diffusion towards the direction opposite to concentration gradient, thus affecting the overall dendritic segregations. This process also works on affecting the precipitation of topologically close-packed (TCP) phase and the evolution of γ/γ′ microstructure. The present work is an important addition to understand the diffusion theory in Ni-SXs.

References

[1] R.C. Reed, N. Matan, D.C. Cox, M.A. Rist, C.M.F. Rae, Acta Mater., 47 (1999) 3367-3381.

[2] T. Grosdidier, A. Hazotte, A. Simon, Materials Science and Engineering: A, 256 (1998) 183-196.

[3] G.E. Fuchs, Materials Science and Engineering: A, 300 (2001) 52-60.

[4] A. Cervellon, S. Hémery, P. Kürnsteiner, B. Gault, P. Kontis, J. Cormier, Acta Mater., 188 (2020) 131-144.

[5] P. Kontis, Scr. Mater., 194 (2021).