*2.3. Tribocorrosion Tests*

The synergistic effect between wear and corrosion (*S*) affects the total material loss rate ( *T*) as

$$T = \mathcal{W}\_{\mathcal{o}} + \mathcal{C}\_{\mathcal{o}} + \mathcal{S} \tag{1}$$

where *Wo* is the wear component in the absence of corrosion and *Co* is the corrosion component in the absence of wear. The synergistic component *S* can be written as

$$S = \ \Delta \mathcal{W}\_{\mathbb{C}} + \Delta \mathcal{C}\_{w} \tag{2}$$

where Δ *Wc* is the change in wear rate due to corrosion, and Δ *Cw* is the change in corrosion rate due to wear. The total wear component is *Wo* + Δ *Wc,* and the total corrosion component is *Co* + Δ *Cw*. These components in a tribocorrosive system will be measured using a combination tribological and electrochemical experiments. The corrosion rate of a material can be obtained using Faraday's law:

$$V\_{\rm cl} = \,\,\mathcal{Q}M/n\mathcal{F}\rho\,\tag{3}$$

where *Vch* is the volume of metal transformed by anodic oxidation, *Q* = *Idt* is the electric charge passed over the time of the experiment, *M* is the atomic mass of the metal, *n* is the charge number for the oxidation reaction, F is the Faraday constant, and *ρ* is the density of the metal. Whereas the wear components will be quantified using the Archard's law [19], the relationship between the hardness of the wear volume can be described as:

$$V/L = \text{ kN/H} \tag{4}$$

where *V* is the volume of wear, *L* is the sliding distance, *N* is the normal load, *H* is the hardness of the softer one in the two contacting materials, and *k* is the wear coefficient, which is valid to both the adhesive and abrasive wears.

Figure 1 schematically illustrates the tribocorrosion test setup used for the experiments. To isolate wear-corrosion synergism in a standard seawater condition of 3.5%wt NaCl, the following series of experiments were performed as per the ASTM G119 [20] for wrought and AM Inconel 718 disks with surface roughness conditions of *Ra* = 0.1 μm. The counter/ball material used will be alumina of 6.35 mm diameter.

