Surface roughness is another important variable for wear. Two-body abrasion is reduced by having smoother surface roughness. For example, a journal or sleeve bearing made out of a softer material will slide against a harder drive shaft with little to no abrasion due to the surface finish. Using materials with similar hardness is generally not advised. The reason for the softer bearing material is to further reduce wear. Contaminants can become embedded into the softer materials and stop three-body abrasion from occurring. This technique might damage the bearing, but is preferred as it is designed to be relatively easy and more cost-effective to replace than a drive shaft. The rougher surfaces can increase the coefficient of friction and micro-peaks can break off, contributing to contaminants that are related to abrasion.
Adhesion
Surface roughness also contributes to adhesion. For this type of wear a material’s compatibility will be important. Compatibility does not mean materials that work well together; rather, that the materials “like” each other, causing them to stick together. This compatibility forms a bond causing parts to seize and even become cold-welded together. There are a few general rules to follow for material selection to make sure unwanted adhesive wear doesn’t occur. Materials that make contact with one another, in general, should:
• Not dissolve in the other
• Not, in given environment and other conditions, form into an alloy
• Not be identical (e.g., an aluminum shaft with an aluminum bearing)
• Have at least one metal from the B-subgroup (e.g., elements to the right of Nickel, Palladium, and Platinum on the periodic table).
Adhesion is possible to calculate. The adhesion and abrasive wear calculations share the same formula; however, it can vary by as much as +/-20%. This inaccuracy is due to constant changing surface conditions and lubrication during operation. It may be better than no data, but designers need to be aware of the limitations and accuracy of the formula. Trying to calculate or predict wear is made more difficult if components have non-conforming geometries, such as when gear teeth and cams are involved. These components can have difficulty staying properly lubricated. To reduce adhesive wear, sometimes corrosive wear is purposely induced.
Corrosive
Chlorides, phosphates, or sulfides can be added to induce corrosion and reduce a more destructive adhesive wear. Corrosive wear is more often thought of as something you want to prevent. Rust, or oxidation, is the No. 1 form of corrosive wear. Lubrication, material selection, surface finish, including coatings—like in abrasive and adhesive wear—are the main factors to consider.
I'm a materials engineering enthusiast with a demonstrated understanding of tribology, the science of interacting surfaces in relative motion. My expertise encompasses the intricate details of surface roughness, wear mechanisms, and material selection for various engineering applications. I've delved into the complexities of two-body and three-body abrasion, adhesion, and corrosive wear, considering the nuances of material compatibility, surface finish, and lubrication.
In the realm of surface roughness and wear, the article rightly points out that surface roughness is a crucial variable influencing wear. In two-body abrasion, smoother surface roughness reduces wear, as seen in the example of a softer journal or sleeve bearing sliding against a harder drive shaft. This scenario minimizes abrasion due to improved surface finish. The use of materials with similar hardness is discouraged, emphasizing the preference for a softer bearing material to further mitigate wear. The rationale is that contaminants can embed into softer materials, preventing three-body abrasion.
Adhesion, another aspect discussed, is influenced by surface roughness and material compatibility. The article emphasizes the importance of materials that "like" each other to avoid unwanted adhesive wear. Specific rules for material selection include considerations such as the materials not dissolving in each other, not forming alloys in the given environment, not being identical, and having at least one metal from the B-subgroup. The article goes on to mention that adhesion is calculable, sharing a formula with abrasive wear calculations, though it acknowledges a potential accuracy variation of +/-20% due to changing surface conditions and lubrication during operation.
The article sheds light on the deliberate induction of corrosive wear to mitigate adhesive wear. By adding chlorides, phosphates, or sulfides, corrosion can be induced, reducing potentially more destructive adhesive wear. Corrosive wear is discussed in the context of preventive measures, with rust or oxidation identified as the primary form. Lubrication, material selection, surface finish, and coatings are highlighted as key factors in addressing corrosive wear.
In conclusion, a comprehensive understanding of surface roughness, wear mechanisms, and material interactions is essential for designing robust and reliable engineering components. The considerations outlined in the article provide valuable insights into optimizing material selection, surface finishes, and lubrication strategies to enhance the performance and longevity of mechanical systems.
