Tribological Characterization of Carbon Based Solid Lubricants

High performance machines such as gas turbine engines demand efficient solid lubricants at high temperature and in vacuum. The current conventional solid lubricants need to be further improved. This research evaluates carbon based solid lubricants using a high vacuum, high temperature pin-on-disc tribometer. The objectives of this research were to develop an understanding of the tribological properties of solid lubricant coatings under extreme operating conditions, and to determine whether using a carbon based solid lubricant would be acceptable for use in those conditions.

Experimentally, two solid lubricant coatings on tungsten carbide substrate were tested against two different materials. The coatings were carbon based and molybdenum disulfide based. The other materials were 440C stainless steel and tungsten carbide. The temperature, pressure, and relative humidity are independent variables. The results showed that the carbon based coating increases friction and wears out quickly due to high temperature, high vacuum, and low humidity. Abrasive wear is the dominating mechanism. At elevated temperatures and in dry environment, the carbon based coating underwent significant oxidation and phase transformation. This research is beneficial for future design and development of solid lubricants for aerospace applications, as well as other industries requiring lubricants that must operate in extreme conditions.

This thesis includes five chapters. Chapter I is an introduction to tribology and to the materials being used in this research. Chapter II describes the motivation and objectives behind this research. Chapter III discusses the experimental procedure and further explains the materials used. Chapter IV presents and discusses the results obtained. Chapter V discusses the major conclusions obtained from the results and offers some future work that may be conducted concerning this research.