**5. Conclusions**

Gradient structures containing an NG surface region have been fabricated in IN718 Ni alloy using the SMGT technique. The thermal stability studies at 700 ◦C up to 100 h resulted in the following observations.


**Supplementary Materials:** The following are available online at https://www.mdpi.com/2073-435 2/11/1/53/s1, Figure S1: (a) STEM image and the corresponding (b–f) EDS maps of the NG layer of the as-processed IN718 alloy., Figure S2: STEM image and EDS maps of (a) thermally stable area and (b) grain coarsened areas of NG IN718 specimen after annealing at 700 ◦C for 24 h.

**Author Contributions:** J.D. and Z.S. fabricated gradient IN718 alloy. B.Y. and Y.Z. performed heat treatment. J.D. and S.X. prepared TEM samples. J.D., Y.Z., Z.S., T.N., J.L. and H.W. performed TEM imaging and results analyses. J.D. wrote the first draft of the manuscript. X.Z. and H.W. conducted data analyses and manuscript preparation. X.Z. and H.W. designed the project and secured funding. All authors have read and agreed to the published version of the manuscript.

**Funding:** DOE-Nuclear Energy under DE-NE0008549 and DE-NE0008787.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

**Acknowledgments:** J. Ding and X. Zhang acknowledge primary financial support by DOE-Nuclear Energy under DE-NE0008549. Z. Shang acknowledges support by DE-NE0008787. S. Xue and H. Wang acknowledge financial support from the U.S. Office of Naval Research (ONR) N00014-20-1- 2043 (for TEM) and N0014-17-1-2087 (for sample preparation). Access to microscopy facilities at Life Science, Birck Nanotechnology Center and School of Materials Engineering at Purdue University, is also acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.
