Lubrication of Titanium Surfaces Modified by Metallic Diffusion

Abstract

Lubrication of titanium by surface modification consisting of diffusion of other metals into the surface was studied. Coatings, approximately 0.001 in., of chromium, cobalt, copper, gold, iron, nickel, platinum, and silver were electroplated on titanium, followed by diffusion at 860 C and 10⁻⁵ mm Hg. Tin and lead were diffused by immersing the titanium in molten baths of these metals. Diffusion bands of approximately 10 to 15 thousandths of an inch were obtained. Coefficient of friction measurements were made at various depths using a series of lubricants containing fatty acids, chloride, sulphide, and phosphite additives. The friction coefficient was reduced from about 0.25, for unlubricated titanium, to 0.06–0.10 in many instances, depending on the metal lubricant combination. Loads of 20 to 40 Kg were sustained by some of the modified surfaces on the Four Ball Tester and 2500 to 3000 pounds on the Falex Machine. With pure titanium, gross seizure occurred at a load of 2 Kg on the Four Ball and 250 pounds on the Falex Machine.