antiwear

Antiwear refers to properties, mechanisms, and additives that reduce wear in mechanical systems, particularly under boundary lubrication when the lubricant film is thin and asperities contact. In lubricants, antiwear additives form protective films on metal surfaces to minimize metal-to-metal contact, limit adhesive wear, and extend component life.

Most AW action is chemical. Under load, additives decompose and react with the metal surface to create tribofilms such as iron phosphates, iron sulfides, or oxides that resist deformation and shear. These films reduce friction, lower peak contact pressures, and prevent scoring or scuffing during high-load events.

Common antiwear additives include zinc dialkyldithiophosphate (ZDDP) in many engine and transmission oils; organic molybdenum and phosphorus compounds; chlorinated paraffins; sulfurized fats; and borate esters. Formulations often balance AW performance with detergents, antioxidants, and friction modifiers to maintain seal compatibility and low ash content.

Applications span automotive engines, transmissions, gearboxes, hydraulic fluids, and metalworking lubricants. In some regions, phosphorus and sulfur limits drive development of low-phosphorus or zinc-free AW chemistries due to catalyst poisoning and environmental concerns. Researchers continue to explore novel tribofilms and solid lubricants for extreme conditions.

Performance is evaluated using standardized tests such as the Four-Ball Wear Test (ASTM D4172), which measures wear scar diameter and friction, along with spectroscopic or tribofilm analysis to characterize protective films.