Tribocorrosion particle-surface reactions

A further complication arises if cathodic reactions take place in the contact zone or in its vicinity because in that case the actual oxidation rate in the contact zone exceeds the measured anodic current. The measured current /measured is th sum of the partial anodic current 4, which represents the oxidation rate in the contact zone, and the (negative) partial cathodic current 1 /measured = 4 + /c- Electrochemical methods are powerful tools for the smdy of tribocorrosion mechanisms in sliding contacts, but they must be complemented by structural and chemical investigations of wear particles and worn surfaces. 

Erosion is one of several wear modes involved in tribocorrosion. Solid particle erosion is a process by which discrete small solid particles, with inertia, strike the surface of a material, causing damage or material loss to its surface. This is often accompanied by corrosion due to the environment. A major environmental factor with significant influence on erosion-corrosion rates is that of flow velocity, but this should be set in the context of the overall flow field as other parameters such as wall shear stress, wall surface roughness, turbulent flow intensity and mass transport coefficient (this determines the rate of movement of reactant species to reaction sites and thus can relate to corrosion wall wastage rates). For example, a single value of flow velocity, referred to as the critical velocity, is often quoted to represent a transition from flow-induced corrosion to enhanced mechanical-corrosion interactive erosion-corrosion processes. It is also used to indicate the resistance of the passive and protective films to mechanical breakdown [5]. 

The most common forms of tribocorrosion are conosion wear, erosion conosion, fretting conosion and microabrasion conosion. Conosion wear can be defined as the degradation of materials due to the combined action of mechanical removal and chemical/electrochemical reactions of the conosive medium. Erosion conosion is associated with degradation of materials by flow-induced mechanical erosion of the material, or the protective (or passive) oxide layer on its surface by impinging liquid, abrasion by slurry, particles suspended in fast flowing liquid or gas, bubbles or droplets, cavitation, etc, and the conosivity of the medium (Stack and Abdulrahman, 2010 Stack et al., 2010a). Erosion conosion is observed in... 

Corrosion is an irreversible surface modification of a material due to chemical reaction with the environment that results in the formation of metal ions dissolved in the liquid (material loss) and, in the case of passive metals, of surface oxide films. A preliminary attempt to include particle flow in tribocorrosion was already proposed by Stemp [11] and Mischler et al [9] to explain the discrepancy mentioned above between first body degradation and mechanical wear. This paper is aimed at developing a phenomenological model of tribocorrosion by combining electrochemical corrosion effects with the third body concept of wear. The approach is applied to three electrochemically controlled wear situations, i.e. wear under cathodic protection (absence of corrosion), wear in presence of passive films and wear combined with metal dissolution. The proposed concepts are compared to already published results concerning carbon steel and stainless steels and their merits are discussed. 

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See also in sourсe #XX -- [ ]

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