Fretting Corrosion: Causes and Prevention

What is Fretting Corrosion?

Fretting corrosion occurs when two surfaces that have been rubbing against one another under significant load. This type of corrosion is also known as chafing corrosion and can be detrimental to materials, reducing their fatigue strength and leading to increased surface roughness and micro pits.

Fretting is a type of wear that occurs as two or more materials are repeatedly moved against each other under a load. Vibration is one of the most common causes of fretting.

The primary factors that contribute to fretting corrosion are the contact force, stress, and relative motion between the two surfaces. In general, the higher the contact force and stress between the materials, the more severe the corrosion. A well-thought-out mechanical design is essential in reducing the impact of corrosion on components.

It is important to note that this form of corrosion is not limited to metals and can occur in various materials in contact. The type of material and the environmental conditions can significantly influence the corrosion mechanism.

Additionally, selecting materials with a higher resistance to corrosion and reducing the surface roughness can help minimize fretting corrosion. Protective coatings or lubricants can also be employed to reduce the impact of this phenomenon.

Understanding the underlying mechanics and the factors contributing to corrosion is crucial in mitigating its effects on components and materials. A combination of proper design, material selection, and preventive measures can go a long way in ensuring the longevity and reliability of components subjected to corrosion.

How to Prevent Fretting Corrosion

Fretting corrosion can lead to degradation and failure of various surfaces and systems, making it essential to implement prevention measures. A vital aspect of corrosion prevention is investing in a robust mechanical design, which includes careful selection of materials and the appropriate manufacturing processes¹.

One technique to prevent corrosion is to address the electrochemical factors contributing to the corrosion process. This can be achieved by applying coatings or employing protective surface treatments that minimize the contact between the two metal surfaces².

Another aspect to consider is the thermal expansion of the materials involved. To minimize corrosion due to thermal expansion, designers should choose materials with similar expansion coefficients or incorporate elements that accommodate temperature-induced movement, such as flexible joints³.

An essential element of combating corrosion is addressing the oxidized material that forms on the surface. This material can lead to further corrosion and should be removed periodically, or its formation can be limited by incorporating a suitable surface treatment. The combination of metals at points of movement can also help reduce fretting corrosion, such as using a hard or strong metal in combination with a softer or less strong one⁴.

Corrosivity can be mitigated by considering environmental factors, such as humidity, temperature, or atmospheric composition. To minimize corrosion, it is essential to select materials and design systems capable of withstanding these factors.

Overall, reducing fretting corrosion involves a multifaceted approach, combining materials selection, surface treatments, and an understanding of the underlying factors contributing to the corrosion process.

Factors Influencing Fretting Corrosion

Fretting corrosion is a form of wear that occurs at the contact points between two materials under load and in the presence of repeated relative surface motion, often caused by vibrations. Several factors influence the occurrence and severity of corrosion, which are discussed in the following sub-sections.

External Mechanical Factors

The external mechanical factors that can influence corrosion include contact load, amplitude, and frequency of the relative surface motion. Higher contact loads typically lead to higher corrosion rates, as the mechanical damage to the surfaces is more severe. The amplitude of the relative surface motion also plays a crucial role, with larger amplitudes causing more aggressive wear. The frequency at which the surface motion occurs can exacerbate fretting corrosion, as higher frequencies are associated with more rapid material degradation.

Properties of Surface and Material

The properties of the contacting surfaces and the materials they are made of also have a considerable impact on fretting corrosion. Factors such as surface roughness, hardness, and reactivity of the material all play a role. For instance, materials with a softer surface or those that are more reactive to the environment are more prone to corrosion due to the ease with which their protective oxide films can be mechanically damaged or removed. Similarly, surfaces with a higher degree of roughness are more likely to experience corrosion, as the asperities on the surface come into contact under load and cause wear.

Atmospheric Influences

Atmospheric conditions surrounding the contact area, such as temperature, humidity, and the presence of corrosive elements in the environment, also contribute to the development of fretting corrosion. Higher temperatures can accelerate the corrosion process due to an increase in the rate of chemical reactions. Humidity can introduce moisture, which can intensify the rate of corrosion if the materials are susceptible to aqueous corrosion. The presence of corrosive elements in the environment, such as chloride ions, can exacerbate corrosion by attacking the passive oxide films on the materials, promoting mechanical damage and further corrosion.

Frequently Asked Questions

What is the underlying mechanism of fretting corrosion?

The underlying mechanism of fretting corrosion involves the combination of two contacting surfaces and the corrosive environment, which results in deterioration at the interface. This damage occurs under load and is induced by repeated motion between the contact surfaces, such as vibrations.

Which materials are most susceptible to fretting corrosion?

Corrosion can affect various materials. Typically, any metallic materials that make contact with each other under load, and when subjected to vibrations, can be susceptible to this type of corrosion. It is important to note that the presence of a corrosive environment, like moisture or harsh chemicals, further increases the risk of oxidation.

How can fretting corrosion in bearings be prevented?

Prevention of corrosion in bearings requires strategies to minimize the conditions that lead to it. These may include reducing vibrations and using proper lubrication to minimize the relative surface motion between the contacting parts. In addition, applying surface coatings or using materials with low susceptibility to corrosion can help reduce the risk of corrosion.

What are common examples of fretting corrosion in electrical connectors?

Fretting corrosion can occur in electrical connectors, resulting in a build-up of oxidized wear and debris when metallic contacts are subjected to small repetitive motions. These motions can be as tiny as a few tens of microns, impairing the conductivity and performance of the connectors over time.

Footnotes

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