*Article* **Thermal Stability of Nanocrystalline Gradient Inconel 718 Alloy**

**Jie Ding 1,\*, Yifan Zhang 1, Tongjun Niu 1, Zhongxia Shang 1, Sichuang Xue 1, Bo Yang 1, Jin Li 1, Haiyan Wang 1,2 and Xinghang Zhang 1,\***


**Abstract:** Gradient structures containing nanograins in the surface layer have been introduced into Inconel 718 (IN718) nickel-based alloy using the surface mechanical grinding treatment technique. The thermal stability of the gradient IN718 alloy was investigated. Annealing studies reveal that nanograins with a grain size smaller than 40 nm exhibited significantly better thermal stability than those with larger grain size. Transmission electron microscopy analyses reveal that the enhanced thermal stability was attributed to the formation of grain boundaries with low energy configurations. This study provides new insight on strategies to improve the thermal stability of nanocrystalline metals.

**Keywords:** nanocrystalline; thermal stability; IN718 alloy
