Contact Mechanics · Tribocorrosion
Tribocorrosion: when wear and corrosion speed each other up
Sliding scrapes the protective oxide film off a metal in salt water, and the bare metal dissolves.
Why does the current jump when sliding starts?
An alumina ball slides on 316L stainless steel in salt water.
Try it: press Stop sliding: the coral fades and the current drops to the passive level. Raise τ to 1 s: the bare part grows from 20% to about 75%.
How much of the loss is wear, corrosion and synergy?
Move the potential and watch the ASTM G119 split T = W0 + C0 + S after a 1 hour test.
Try it: press Cathodic: only grey wear is left. Press Breakdown on 316L: the coral takes over. Ti-6Al-4V stays passive.
What to take away
The film is the key
Steel and titanium resist corrosion because of an oxide film a few nanometres thick. Sliding scrapes it off.
Synergy can be large
Corrosion alone (C0) is usually tiny for a passive metal. The extra loss comes from the two acting together.
Potential sets the split
In this model, cathodic protection leaves only mechanical wear. Above the breakdown potential, corrosion takes over.
More detail: the equations, the numbers and the limits of this model
Picture 1: active area model
The ball strips the film fully each time it passes. After that, the bare fraction of each point falls as exp(−t/τ), with t the time since the last pass. The current is I = ibare Aactive + ip A0: bare track area times a bare-metal current density, plus the passive current on the whole 1 cm² sample. This is the depassivation and repassivation picture used by Landolt, Mischler and co-workers, in its simplest form. When τ is much shorter than the time between passes, the mean current is about ibare w τ (2Lf), so it grows in proportion to f and τ.
Numbers in picture 1
Stroke L = 10 mm, sinusoidal motion, 6 mm alumina ball (E = 380 GPa, ν = 0.22) on 316L (E = 193 GPa, ν = 0.30). Track width w = 2a from Hertz, a = (3PR/4E*)1/3; real worn tracks are wider. The bare-metal current density ibare = 20 mA/cm² and the passive current density ip = 0.5 µA/cm² are illustrative values of the right order, not measured for one test. Measured repassivation times are often in the millisecond range; the slider goes up to 2 s so that the regrowth can be seen.
Faraday's law
M = I t A / (n F) and V = M / ρ, with F = 96 485 C/mol. For an alloy, A/n is the equivalent weight EW from ASTM G102: 25.50 g for type 316 (Fe2+, Ni2+, Cr3+, Mo3+), with ρ = 7.98 g/cm³. For Ti-6Al-4V the page uses Ti4+, EW = 11.98 g, and ρ = 4.43 g/cm³.
Picture 2: the G119 split
ASTM G119 measures the total loss T in the corrosive test, the wear alone W0 under cathodic protection, and the corrosion alone C0 without sliding. The synergy is S = T − W0 − C0 = ΔCW + ΔWC: extra corrosion caused by wear, plus extra wear caused by corrosion. The fixed test here is 10 N, 10 mm stroke at 1 Hz for 1 hour (72 m of sliding).
| Input (illustrative) | 316L | Ti-6Al-4V |
|---|---|---|
| Open circuit potential (V vs SCE) | −0.25 | −0.35 |
| Passive current density | 0.5 µA/cm² | 0.5 µA/cm² |
| Breakdown potential (V vs SCE) | +0.35 | above +1.0 |
| Wear coefficient k, W0 = k P s | 3 × 10⁻⁵ mm³/Nm | 1.5 × 10⁻⁴ mm³/Nm |
| ΔWC as a share of W0 (passive) | 30% | 20% |
C0 uses the static anodic current on the track area. The dashed sliding curve is the current of the whole 1 cm² sample. ΔCW uses the picture 1 current at the default settings (τ = 0.1 s), scaled up with potential and above breakdown. These trends follow the published picture for passive metals, but the sizes depend strongly on the metal, the solution and the rig.
What the model leaves out
It has no third bodies (trapped debris), no change of contact shape with wear, no galvanic coupling between the bare track and the passive surface around it, and one constant friction and wear coefficient. At open circuit, that galvanic coupling makes the sample potential drop when sliding starts; a potentiostat, as in picture 2, holds it fixed instead.
Questions people ask
What is tribocorrosion?
Tribocorrosion is damage from wear and corrosion acting at the same time on a sliding, rolling or fretting contact in a corrosive liquid or gas. The two effects feed each other, so the loss is not the sum of the two measured apart. It matters for hip and knee implants, pumps and valves, marine parts and food processing equipment.
What is a passive film?
It is an oxide layer a few nanometres thick that forms on its own on metals such as stainless steel, titanium and cobalt-chromium. It slows corrosion by a very large factor. When it is scratched away, the bare metal below dissolves quickly until the film grows back.
Why does the open circuit potential drop during sliding?
The bare track has a much lower potential than the passive surface around it. The two are joined through the metal, so the measured potential is a mix and moves down toward the bare metal value. When sliding stops and the film regrows, the potential climbs back.
How does ASTM G119 measure synergy?
It runs the wear test three ways: in the corrosive liquid (total loss T), under cathodic protection so that there is no corrosion (W0), and without sliding (C0). The synergy is what is left over: S = T − W0 − C0. Measuring the current during sliding splits S further into ΔCW and ΔWC.
Can synergy be negative?
Yes. Sometimes a corrosion product or a thick film protects the surface or lowers friction, and the total loss is smaller than W0 + C0. Watson and co-workers discuss such cases in their review of synergy test methods.
How do you reduce tribocorrosion?
Lower the mechanical side with harder surfaces, coatings or better lubrication, or lower the chemical side with a metal whose film regrows quickly and dissolves little. Cathodic protection can remove the corrosion part in some systems. The best choice depends on which term, W0 or S, is the larger one.
On this site: Wear mechanisms and wear depth · Tribofilms and third bodies · Fretting and partial slip · Wear rate calculator · Asperities and the real area of contact
References
Show the 7 references
- D. Landolt and S. Mischler (eds.), Tribocorrosion of Passive Metals and Coatings, Woodhead Publishing, Cambridge (2011).
- S. Mischler, Triboelectrochemical techniques and interpretation methods in tribocorrosion: a comparative evaluation, Tribology International 41 (7), 573 to 583 (2008). doi:10.1016/j.triboint.2007.11.003
- ASTM G119-09 (reapproved 2021), Standard Guide for Determining Synergism Between Wear and Corrosion, ASTM International.
- A. Igual Muñoz, N. Espallargas and S. Mischler, Tribocorrosion, SpringerBriefs in Applied Sciences and Technology, Springer (2020). doi:10.1007/978-3-030-48107-0
- S. W. Watson, F. J. Friedersdorf, B. W. Madsen and S. D. Cramer, Methods of measuring wear-corrosion synergism, Wear 181 to 183, 476 to 484 (1995). doi:10.1016/0043-1648(95)90161-2
- ASTM G102-89 (reapproved), Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements: equivalent weights (type 316: 25.50 g; Ti4+: 11.98 g).
- K. L. Johnson, Contact Mechanics, Cambridge University Press (1985): chapter 4, Hertz contact radius.
BibTeX
@misc{tripathy2026tribocorrosion,
author = {Tripathy, Manisha},
title = {Tribocorrosion Lab},
year = {2026},
howpublished = {\url{https://untetheredatom.com/tribology/tribocorrosion}},
note = {Interactive web tool}
}