TRIBOLOGICAL COMPARISON AND DESIGN SELECTION OF HIGH-TEMPERATURE CANDIDATE CERAMIC FIBER SEAL MATERIALS

This paper describes a research program to evaluate ceramic fiber material candidates for high-temperature seal applications. To select a material and incorporate it in an advanced ceramic fiber seal, a comparison of tribological properties must be made, taking into consideration anticipated use conditions such as seal loads, temperatures, and sliding velocity. To this end, pin-on-disk tests were used to evaluate potential seal materials by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Tests were conducted in air under a 2.65 N load, at a sliding velocity of 0.025 m/sec and at temperatures from 25-degrees to 900-degrees-C. Friction was measured during the tests, and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. For the conditions studied, oxide-based fibers were generally superior to carbide-based fibers. A dimensional analysis of the wear data shows that the fiber durability is related to a dimensionless durability ratio which represents the ratio of the fiber strength to the fiber stresses imposed by sliding. The analysis lends insight into fiber performance under these test conditions and may be useful in predicting material behavior based upon measured properties such as fiber diameter, tensile strength, and test load.