**4.3 Analysis and interpretation of sliding test results**

The total wear Wtr in a wear track of area Atr can be expressed as a sum of components related to both types of areas present on the track, the area Aact in active state, and the area Arepass in re-passivated state:

$$\mathbf{W}\_{\rm tr} = \mathbf{W}\mathbf{\dot{c}}\_{\rm act} + \mathbf{W}\mathbf{\dot{m}}\_{\rm act} + \mathbf{W}\mathbf{\dot{c}}\_{\rm repuss} + \mathbf{W}\mathbf{\dot{m}}\_{\rm repuss} \tag{37}$$

with :

102 Corrosion Resistance

track is small compared to the resistance Rpass of the area of the sample remained in passive state, outside of the sliding track: if Ract << Rpass, according to equation (29), the measured

In the preceding steps, two extreme cases were characterized, namely on the passive material and on the active one repectively. Under tribocorrosion conditions at high latency time, the surface of the material undergoes sequential events of depassivation and repassivation in-between successive contacts. This means that a part of the surface at any given time repassivates progressively. The latency time is then selected so that the regrowth of a surface film between two successive contact events is not anymore negligible as it was the case under sliding at low latency time. To achieve partially active sliding tracks, the latency times can be selected as tlat2 = treac/1000 and tlat3 = treac/100 (Diomidis et al., 2009). As a result of the increase of the latency time in this step, the wear track can now be assumed to


It must be stressed that under continuous sliding, these active and repassivated areas remain constant because of stationary electrochemical state conditions. Under intermittent sliding, these active and repassivated areas on the sliding track evolve with time between two successive contact events since a gradual increase of the coverage of the repassivated area takes place within the ''off period''. By hypothesis, in both cases, the fraction of the sliding track surface covered by the passive film, Arepass/Atr, is assumed to be constant and

> repass lat tr reac

act lat tr reac A t <sup>1</sup>

At the latency times tlat2 = 0.001 treac and tlat3 = 0.01 treac, the relationship between repassivated and total wear track area are respectively Arepass 2 = 0.001Atr and Arepass 3 = 0.01

Atr, and thus the active wear track areas are Aact 2 = 0.999 Atr and Aact 3 = 0.99 Atr.

A t

AA A tr act repass (34)

A t (35)

A t (36)

**4.2.4 Third step in the testing protocol: Electrochemical tests on a partially active** 

resistance Rps gives then straight an approximate value of Ract.

consist of two distinct zones (Diomidis et al., 2010), namely:

repassivated area, Arepass with:

given by the ratio tlat/treac:

and:

**sliding track during sliding** 


In order to assess the values of these different components and to compare them to determine the characteristics of the wear mechanism, the following analyses have to be performed:


Detailed information on the analysis and related interpretation of sliding tests can be found in a Handbook on Tribocorrosion (Celis & Ponthiaux, 2011).
