Friction and Wear of Hexagonal Metals and Alloys as Related to Crystal Structure and Lattice Parameters in Vacuum

The friction and wear characteristics were determined for fourteen hexagonal metals in vacuum at temperatures to 850 F and sliding speeds to 2000 fpm. The metals examined included cobalt, titanium, zirconium, hafnium, beryllium, the rare earth metals, and binary alloys of some of these with other elements. Single crystals of cobalt were also examined to determine the influence of specifically oriented planes on friction. Differences in friction properties of these metals (e.g., cobalt and titanium) were found to be related to crystal slip systems and associated shear. Friction coefficients are further related to lattice parameters for fourteen hexagonal metals. For those hexagonal metals undergoing crystal transformation to a cubic form at elevated temperatures, marked changes were observed in friction and wear with the crystal transformation. While relatively moderate friction and wear is observed for the hexagonal form, high friction and complete welding is observed for the cubic structures. Selective alloying of other elements with these hexagonal metals was found to expand the crystal lattice and to delay crystal transformation, thereby improving friction and wear characteristics.