Wear and Compatibility Behavior of Liquid Metal Bearing Materials

The wear and compatibility characteristics of selected bearing materials, including surface coatings and cemented refractory carbides were investigated in support of a pump development program for advanced Rankine cycle space power plants employing high temperature lithium and NaK. Compatibility of candidate materials with 1100-deg lithium in Cb-1 Zr alloy was studied in tilting capsule tests for durations to 7000 hr. The wear behavior of material combinations was evaluated with a rotating disk-static shoe assembly in lithium and NaK to 1000 deg. The best compatibility and wear characteristics were exhibited by high density molybdenum cemented carbides. Carburized Cb-1 Zr alloy wear resistance was inconsistent but, under the best conditions, was nearly equivalent to that of the cemented carbides. Plasma sprayed coatings of tungsten carbide and WC-Co gave encouraging results in NaK, but additional development of the coating process appeared necessary to assure reliable control of adhesion and performance.