Tribological performance of titanium doped and pure DLC coatings combined with a synthetic bio-lubricant

Thermal degradation of environmentally friendly lubricants prevents the spread of its utilisation in industrial applications. This process can be promoted by frictional heating occurred during accidental contacts of moving parts or star-up and shut-down operations. The use of low friction coatings, like diamond-like carbon (DLC), can offer a solution to these problems. Their low friction properties, high wear resistance and excellent corrosion resistance can prevent the occurrence of such local heat spikes, which will protect the lubricant and hence prolong the lifetime of the tribological system. In this work, a synthetic bio-lubricant has been evaluated and compared with a mineral oil. Combinations with pure and Ti doped DLC coatings were taken into account. In order to have a proper evaluation of the tribosystem a wide range of conditions have been considered in high frequency reciprocating and unidirectional tests. The Stribeck curve at variable sliding speeds and loads was obtained. In steel/steel contacts friction is clearly lower when synthetic oil is used compared to a mineral based oil, which is not always true with DLC/DLC contacts. As a result of the tribotesting, the best combination of materials was.chosen in order to be validated in a real system (mechanical component in a machine tool), where results confirmed our expectations. (c) 2005 Elsevier B.V. All rights reserved.