Evaluation of Tribological and Cooling Performance of TiN and DLC-Coated Pistons for Miniature Stirling Cryocooler

The Stirling cryocoolers are widely used in the military and aerospace fields due to advantages such as high efficiency and compact structure. The pistons of these coolers with very small clearances operate at high speed and without lubrication. Piston failure in the coolers has often affected the operational life of the cooler. The objective of the study was to find a solution to piston failure by providing a surface coat to the pistons, carrying out their tribological evaluation, and analyse cooler thermal performance to identify the better of two coatings for field applications. In the present experimental study, a Stirling cooler developed with a cooling capacity of 0.5 W @80 K with Helium as the working fluid was integrated with surface-coated pistons and tested for its mechanical and thermal performance. On testing, DLC coating exhibits better wear resistance than TiN coating and therefore is a more suitable coating for cryocooler pistons. The present study clearly shows that DLC-coated pistons reduce power consumption and increase the number of operational hours of miniature Stirling cryocoolers.