*2.2. Intergranular Corrosion Test (NAMLT)*

The specimens were sensitized at 100 ◦C for 0, 3, 7, 48, 144, and 207 h prior to corrosion testing. A nitric acid mass-loss test (NAMLT, ASTM G67) was used to determine the IGC susceptibility [20]. According to the standard, the test specimen was machined into blocks. The surfaces of the blocks were polished with 320 grit abrasive paper, and the specimen dimensions were measured to the nearest 0.02 mm. Before the test, the samples were etched in 5% NaOH (1 min at 80 ◦C). The initial mass of each specimen was measured on a digital scale. The samples were then immersed in 70% HNO3 for 24 h. After the test, all specimens were carefully rinsed with water and brush with a stiff plastic brush. The final weight of the specimens was measured and used to calculate the mass-loss rate [20].

Microstructural evolutions of the alloys were investigated by optical microscopy (OM, Nikon MA200, Nikon, Tokyo, Japan), scanning electron microscopy (FE-SEM/EDSFEI Quanta200F, Hitachi, Japan), electron backscatter diffraction (EBSD, EDAX Hikari EBSD detector, Mahwah, NJ, USA), and transmission electron microscopy (TEM, JEOL JEM-2100F, Akishima, Japan). The obtained EBSD data were analyzed using the MTEX software (open-source MATLAB toolbox) [21]. Image J software (open-source Java image program, NIH Image) was used to calculate the maximum intergranular corrosion depth and area.
