*2.1. Materials and Processing*

The IN718 Ni-based alloy with a chemical composition as listed in Table 1 was subjected to SMGT. Prior to processing, a cylindric bar was solution-treated at 1100 ◦C for 1 h followed by water quenching (denoted as as-processed hereafter). During processing, the bar was rotated at a velocity of 400 rpm while a WC/Co tool tip penetrated into the surface by 30 μm and slid along the axial direction at a speed of 10 mm/min. The process was repeated 8 times to generate a substantial deformation zone. Liquid nitrogen was used as the coolant during processing. Subsequently, the processed samples were annealed in a vacuum furnace at 700 ◦C for 5, 24 and 100 h, followed by furnace cooling. Annealing was conducted when the vacuum reached 2 × <sup>10</sup>−<sup>6</sup> torr.

**Table 1.** The chemical composition of IN718 alloy (in wt.%).

