**7. Future developments**

In the quest for higher-performance turbine engines, a number of changes are under devel‐ opment. Possibly the most significant is the development of harder and more corrosionresistant metal alloys such as Pyrowear and CSS22, among others, hard coatings such as TiC, and low-density silicone nitride–bearing materials. These materials are designed for high load carrying and higher temperature, which leads to challenges in lubricant stability. Harder and more stable coatings will allow for higher temperatures and loads adding stress to the lubricant system. It may be necessary to develop new basestocks that have wider liquid ranges and greater thermal stability.

More importantly, all of these new bearing materials have radically different surface chemistry than traditional steel-based bearings. The additive packages, particularly boundary lubrica‐ tion additives, are dependent on the presence of an oxide or hydroxide surface coating to react with. The new bearing materials have a surface chemistry dominated by the presence of carbides or nitrides. The data are uncertain as to the level of surface coverage and the reactivity of the phosphate esters with these new surfaces.
