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Corrosion and Wear (Tribology)

Corrosion and wear are modes that occur over time and have been categorized in the study of tribology. Corrosion is the process of oxidation when moisture is present; a popular example is rusting of iron. When rust melts, it flakes off and leaves a surface more prone to continuous corrosion, causing material to wear away and degrade the quality of the part. The deterioration of metal causes serious damage to electronics equipment and critical components of engines and aircraft.

In order for corrosion to occur, there needs to be a corrosive metal, water and oxygen. Aluminum is prone to rust more than iron, but the thin layer that appears on aluminum protects the metal from further deterioration. Gold and silver are less prone to rusting.

Corrosion can be prevented or at least deterred by implementing corrosion resistant materials to protect critical components. Plating, painting, greasing or other barriers are put up to avoid moisture and air, thus reducing the corrosion effect.

When parts wear, material is removed and the integrity of the part is compromised, therefore unable to perform its function reliably. When designing engine components, railroad systems, waterway lock-gates or roller bearings, understanding corrosion and wear is critical in aiding the metallurgical engineers and other teammates to choose the optimal configuration and material for the parts. Wear resistant and corrosion resistant coatings and grease will improve the design and ensure a longer life of the components.

When stresses are high during a corrosion experience, cracking may occur. This stress-corrosion cracking is highly detrimental to the part integrity and can cause quick degradation and failure modes. Another serious corrosion and wear mode is lubrication starvation. Water, air and a corrosive metal will produce a problematic effect, and without lubrication can cause complete failure of a system. Lubrication or grease is a common cure or band-aid for an area that is prone to wear. When lubrication is absent, these areas become over stressed, leading ultimately to failure.

Abrasive wear and erosion damage are common in high stress situations. Abrasive wear is intense rubbing which causes erosion of the material. Erosion of material weakens the system as a whole and thus minimizes the efficiency of the system. When cavitation occurs, corrosion is creating pits or cavities within the material, essentially subtracting mass and strength of the alloy or base metal.