SLIDING FRICTION AND WEAR OF METALS IN VACUUM

Sliding friction and wear in vacuum were studied for 16 combinations of four pure metals (copper, nickel, iron and molybdenum) from the points of view of adhesion energy and hardness ratio H(d)/H(p) (ratio of hardness of disk to hardness of pin) before and after the test. It was found that severe wear usually occurred when the range of hardness ratio H(d)/H(p) after the test included values below about 1.0. Mild wear typically occurred when this ratio included only values above about 1.0. It was also found that friction and wear behaviour were dependent on the adhesion energy and the crystal structure. Mutual transfer was observed in both wear modes for every combination of different metals. Transfer ranged from widely scattered local transfer to relatively uniform transfer. Three types of wear debris were observed in severe wear: plate-like, wedge-like and cylindrical-spherical debris. Although wear debris consisted mainly of disk material, it also commonly contained pin material existing as small scattered pieces. The size of wear debris was strongly dependent on the hardness of the disk material and the adhesion energy. The data from self-mated tests were consistent with those using two different metals.