Antifriction properties of some composite sintered packing materials. II

Summary

The addition of more than 20 vol.% of solid lubricants to the materials investigated is undesirable, because it adversely affects their strength properties and increases their coefficients of friction and specific wear, with increasing rubbing velocity and pressure, high temperatures are generated in the friction surface zone, resulting in the oxidation of the solid lubricant and the metallic matrix of the materials and formation of oxides on the surface. The presence of oxides on the friction contact surface inhibits the propagation of thermal seizure processes, in consequence of which specific wear and the coefficients of friction decrease. Conversely, the burning out of graphite solid lubricant is responsible for the deterioration of the antifriction properties of materials. As a result of this, with increase in rubbing velocity, the coefficients of friction and specific wear of materials with additions of chemically stable solid lubricants decrease, while those of nickel-graphite materials increase.

On the basis of the investigations described, natural mica (phlogopite) and boron nitride may be recommended as substitutes for graphite as solid lubricants in packing materials. From the point of view of operation in packing elements of gas-turbine engines, the best combination of antifriction properties is offered by sintered composite nickel-mica and 20Cr-80Ni alloy—boron nitride materials.