*3.1. Wear Volume during Tribocorrosion*

The wear behavior was measured for wrought and AM Inconel 718 during the OCP, potentiodynamic, and cathodic polarization tests. The wear volumes with respective wear track profile results for the wrought sample are presented in Figure 2 and for the AM sample are presented in Figure 3. The wear tracks were profiled and analyzed using a 3D optical profilometer. The 3D profiles were used to accurately extract the wear volume under each test condition and were compared. It can be observed in Figure 2 that the wrought Inconel 718 undergoes wear of 2.57 mm<sup>3</sup> under the influence of corrosion and wear during the potentiodynamic test. The wear under OCP conditions in the sample is in equilibrium potential with the corrosive environment and is found to be 2.28 mm3. Under cathodic polarization conditions, the effects of corrosion have been electrochemically removed to isolate the wear under the given corrosive environment; the wear is found to be 1.15 mm3.

**Figure 2.** Wear on wrought Inconel 718 after (**a**) potentiodynamic test, (**b**) OCP condition, and (**c**) cathodic polarization test shown alongside a common color scale bar.

**Figure 3.** Wear on AM Inconel 718 after (**a**) potentiodynamic test, (**b**) OCP condition, and (**c**) cathodic polarization test shown alongside a common color scale bar.

Comparing the potentiodynamic and OCP wear volume results, it is observed that the wear is accelerated due to the onset of corrosion by a factor of 11.28% in the corrosive environment. It is believed that this is due to the small roughness reduction initially at the onset of corrosion, exposing the corrosion surface area and oxide film defect, increasing the susceptibility to corrosion product formation [22]. The corrosive environment itself seems to have a significant influence on surface degradation, as when the OCP and cathodic polarization wear volumes are compared, the wear seems to increase by 49.5%. The synergistic effect considering the corrosion accelerated wear in the corrosive environment the wear volume increased by 55.25%. This shows the drastic effect of aqueous corrosive environment on wrought Inconel 718.

In Figure 3, it can be observed that for AM Inconel 718, the potentiodyanamic wear volume is 1.22 mm3, the OCP wear volume is 1.71 mm3, and the cathodic polarization wear volume is 1.21 mm3. It is evident from comparing the OCP and cathodic polarization wear conditions that the corrosive environment increases the wear by 29.24% without the initiation of corrosion. It is interesting to note from the potentiodynamic polarization and OCP wear volumes that the initiation of corrosion actually decreases wear volume by 28.7%. This indicates that the AM Inconel 718 has a directional solidification during its fabrication and can be equal to or exceed the mechanical properties of wrought counterpart,in this case it is observed as reduced wear volume. Studies have shown that the corrosion resistance of the AM Inconel 718 samples increases with the increasing incline angle of LPBF process, and this can be rationalized by considering changes to the grain boundary area [16]. The synergistic effect considering the corrosion accelerated wear is found be extremely low at only ~1% increase in wear volume. It is expected that there is a small degree of electropolishing that occurs on the surface of the AM Inconel 718 in tribocorrosive environment, which can increase pitting corrosion resistance [23]. These results indicate that AM of Inconel 718 has a significant influence on the tribocorrosion performance as compared to the wrought counterpart. The corrosion results are further investigated in the following section.
