Starved Lubrication using Ionic Liquid as an Additive to Biodegradable Oil in Titanium-Ceramic Contact

Friction leads to energy loss in any system that has two bodies in contact and relative motion with each other. Advancements in lubricants and the lubrication process have helped to reduce friction and in return reduced energy losses owing to friction. But, however, lubricant starvation is still a reality and can happen in applications like piston-ring and cylinder liner contact, and machining etc. It can cause equipment damage leading to unexpected downtime. Ionic liquids, in the recent years have shown a great potential in terms of friction and wear reduction. Using ionic liquids as additives helps reduce the cost of the lubricant considering the high cost of ionic liquids. Mineral oil based lubricant have been very commonly used as the base lubricant. However, they have caused environmental concerns due to the presence of petroleum-based products. The use of biodegradable oil as the base lubricant has proven to be a great alternative. The advancements in composite materials have made the range of materials that we use today more versatile. However, the potential of some monolithic metals like titanium remains unexplored. The major reason for the limited application of titanium is not the limited availability of the metal, but the high cost of machining titanium itself. Ceramic tools are the most commonly used in titanium machining. This study focusses on using an ionic liquid as an additive to a biodegradable oil in starved lubrication regime in titanium-ceramic contact at 3 different frequencies under different loads. Tests were conducted using a reciprocating tribometer with a tungsten carbide ball in contact with the titanium disk. Tests were performed at frequencies of 3Hz, 4Hz and 5Hz. The results showed a maximum 50% reduction in friction coefficient and 23% wear reduction at a frequency of 5 Hz under a load of 2N by using the ionic liquid as an additive to biodegradable oil as compared to using the biodegradable oil as the base lubricant. A maximum wear reduction of 28% was achieved at frequency of 5 Hz under a load of 3N. Moreover, the use of 1% wt. ionic liquid as an additive delayed the spike in friction coefficient by almost 40% as compared to using biodegradable oil as base lubricant. Scanning Electron Microscope analysis showed fewer abrasion marks on the wear track achieved by using 1% wt. protic ionic as additive to biodegradable oil as compared to using biodegradable oil as base lubricant. Energy Dispersive X-ray Spectroscope (EDS) results showed higher amount of carbon inside the wear track when the ionic liquid was present in the lubricant, that proved the presence of a tribolayer