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

This paper describes a research program to evaluate ceramic fiber mate rial candidates for high-temperature seal applications. To select a ma terial and incorporate it in an advanced ceramic fiber seal, a compari son of tribological properties must be made, taking into consideration anticipated use conditions such as seal loads, temperatures, and slid ing velocity. To this end, pin-on-disk tests were used to evaluate pot ential seal materials by sliding a tow or bundle of the candidate cera mic 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 tempe ratures from 25-degrees to 900-degrees-C. Friction was measured during the tests, and fiber wear, indicated by the extent of fibers broken i n the tow or bundle, was measured at the end of each test. For the con ditions 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 impos ed by sliding. The analysis lends insight into fiber performance under these test conditions and may be useful in predicting material behavi or based upon measured properties such as fiber diameter, tensile stre ngth, and test load.