Although there seems to be no obvious relative motion between the two parts, the contact surface is worn. For example, the wear between the outer ring of the bearing and the bearing seat hole below.
The two parts are clearly lubricated and there is no relative motion, but soon there are signs of rust, such as the "red rust" at the spline fitting in the figure below.
What happened? This is what we are going to learn about today: Fretting Corrosion.
Fretting corrosion refers to the progressive surface damage that occurs in the contact area of two metals. It is caused by very slight swings, vibrations or sliding between the metal surfaces (even as low as the nanometer level) plus corrosive erosion of the environment.
The most common influence of the external environment is oxidation. When there is a micromotion between the two parts, the metal at the high point of contact is deformed and peeled off from the surface into fine particles through mechanical cyclic motion. They are then oxidized and trapped between the micromotion surfaces. Some fall into the low-lying areas of the micromotion surface, and some oxide particles continue to act as abrasives on the contact surface, increasing the material removal rate. After metal wear, if a new passivation film cannot be formed in time, the wear will be aggravated.
The above is a basic principle of fretting corrosion. So how should we avoid it?
1. To prevent fretting corrosion, the first thing is to prevent "fretting". This may include design changes, selecting appropriate tolerances, improving fit accuracy, suppressing any possible vibration, ensuring that all joints are properly tightened, etc.
2. Shot peening is performed on the contact surface to produce plastic yield and residual compressive stress on the surface to improve resistance to fretting fatigue
3. Apply anti-fretting agent coating
4. Use better lubricants and increase the frequency of lubrication.(来源：iMechanics机械)
