Influence of Crystal Structure on Friction Characteristics of Rare-Earth and Related Metals in Vacuum to 10−10mm of Mercury

Friction, wear, and metal-transfer characteristics were determined for rare-earth and related metals in vacuum to 10−10 mm of mercury. The metals studied were lanthanum, neodymium, praseodymium, cerium, holmium, erbium, gadolinium, dysprosium, samarium, yttrium, and thallium. Friction and wear experiments were conducted with the rare-earth or related metals generally sliding against 440-C stainless steel. The results of the investigation indicate that crystal structure considerations and polymorphism can explain the friction, wear, and metal-transfer characteristics of the rare-earth and related metals in vacuum. Close-packed hexagonal crystal forms of the rare earths and thallium had much lower friction, wear, and metal-transfer characteristics than face-centered or body-centered cubic structures.