**4. Consensus on the need of materials for triboelectrochemistry systems**

oxidation resistance due to the absence of oxide grain boundaries, which provide a rapid diffusion path for concentration gradient-driven ion movement [46]. In aqueous solutions, ion transport is mostly driven by the electric field across the oxide film. The lack of oxide grain boundaries may lower ion migration rates, rendering the passive film more protective

**Figure 4.** Schematic diagrams of anions adsorption and characteristics of passive films (bi-layer structure) formed on Fe-based amorphous alloy in (a) sulfate and (b) chloride solutions. (reproduced from Wang et al. [47] with permission

It is worthwhile to mention that if the passive films on metals, like iron, nickel, and chromium, remained intact, then the corrosion current flowing across the interface under most industrial conditions would be of the order of 0.01–1.0 μA.cm−2, corresponding to corrosion rates of approximately 0.15–15 μm per year [49]. For most practical situations, metal loss rates of this order are of no concern, so that our automobiles, bridges, aeroplanes, and industrial systems would last for periods extending well beyond the current design lifetime. Unfortunately, passive films do not remain intact, and corrosion rates of many orders of magnitude greater than those indicated above for fully passive substrates are commonly observed, particularly if the

Passivity breakdown can occur for a variety of reasons, including mechanical straining of the substrate metallic alloy, the frictional dissipated energy in tribological contacts required for micro-cracking, the presence of thermal stresses within the oxide due to differences in thermal expansivity, compressive stresses in the oxide growth (Pilling–Bedworth ratio), fluid flow and cavitation, transpassivity polarization, and chemically-induced phenomena. In particular, the rapid transport and accumulation of cation vacancies at the oxide/metal

[46, 48].

from Elsevier Science).

92 Metallic Glasses - Properties and Processing

attack occurs locally.

The development of tribocorrosion resistance requirements has resulted in the development of a much larger number of materials that did not exist before, especially metallic alloys. In turn, such a development of materials has multiplied case studies, and increased the number and the diversity of corrosion-wear problems. Accordingly, the resolution and the nature of corrosion-wear problems are intimately related to the choice of materials. This does not mean that the tribocorrosion resistance is necessarily the determining parameter in the choice of a given material. Such a choice must, in fact, make it possible to fulfill at best one or more technological functions, and it is quite obvious that, under such conditions, the mechanical properties of the materials, their properties of implementation, their price or their availability are in many cases, parameters are just as decisive in the choice as their only resistance to tribocorrosion.
