Influence of Near-Surface Severe Plastic Deformation on the Corrosion Behavior of GTD-111 Nickel Superalloy in Hydrofluoric Acid Solution

High-energy shot peening (HESP) as a common near-surface severe plastic deformation (NS-SPD) was used to create a severely deformed surface with ultrafine grains and dense crystallographic defects (e.g., grain boundaries, dislocations, and twins) on GTD-111 Ni superalloy. The fluoride-induced corrosion performance of HESPed GTD-111 and its solution-annealed counterpart is comparatively studied using immersion tests, grazing-incidence x-ray diffraction analysis, electrochemical techniques, and glow discharge optical emission spectroscopy (GDOES). As supported by the immersion tests and electrochemical measurements, HESPed GTD-111 exhibits corrosion film with higher resistance and lower passivity current density at the expense of a higher initial corrosion rate. Both samples suffer pitting corrosion; however, the solution-annealed one shows deeper and larger pits. The dense distribution of crystallographic defects on the surface of the HESPed sample significantly increases the diffusion of alloying elements to the corrosion front. The GDOES depth profiles reveal that (i) a thicker corrosion film with a higher contribution of alloying elements (namely, Cr, Ti, Co, and Al) is developed on the HESPed sample, and (ii) the corrosion films formed on the solution-annealed and HESPed samples consist of an outer F-rich part and an inner O-rich region. The protective mechanism of NS-SPD is discussed by a physical model.