Ceramic Composite Materials Investigated for Suitability in Dynamic Sealing Conditions

Abstract Dynamic face seals are used in rotating aerospace (engine gearbox and drive shaft) and industrial applications to maintain pressure differentials, prevent fluid leakage, and protect equipment from the external environment. Current dynamic face seal applications use a carbon stator due to carbon’s self-centering and self-lubricating properties. Carbon stators cover a wide range of applications but have limited use in both low speed-high load and high-speed applications. Current alternate materials used in these applications include carbides such as self-sintered silicon carbide (SiC) and cemented tungsten carbides (WC) with cobalt or nickel additions. This work investigates alternative ceramic materials for improved performance in these particular environments. Ceramic composites of alumina with a lubricating oxide show promising low friction properties. This study investigates the effect of Al2O3 and alternate metal oxide molar ratio, pressing load, and binder content on the materials performance. The novel ceramic material has higher compressive strength than carbon which, in a homogenous structure, prevents the particulate breakdown that causes excessive wear in carbon at low speed-high load applications. Additionally, the ceramic system will not experience phase changes (unlike the oxidation of graphite or SiC) so mechanical properties are constant at the high temperatures induced by high rotational speeds. Linear reciprocation testing was performed at variable loads with a 6% cobalt binder WC contacting pin. Friction testing, profilometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to analyze the effect of wear, surface roughness, density, and phase composition; all tests were replicated on carbon and carbide materials for comparison. Low alumina powder ratios with smaller alumina starting powder size demonstrated the lowest dynamic coefficients of friction, most similar to the performance to carbons. A dynamic testing rig will be used in future testing on the best performing ceramic systems in similar service conditions experienced by dynamic face seals.