Friction of Clean Metals and Oxides with Special Reference to Titanium

Abstract

The friction coefficients of freshly cut surfaces in inert atmosphere are compared with values on the same surfaces later exposed to air. The kind of metal or oxide comprising the friction couple was also varied. From experimental data it was concluded that: (1) Solid phase welding accounts for almost the entire magnitude of the static friction coefficient for metal‐metal couples. (2) Fe‐Ag does not solid phase weld, other insoluble couples examined do weld. (3) A measure of solid phase weldability appears to be the quotient of the work of adhesion and the shear strength of the weaker couple. (4) Titanium does not solid phase weld to crystalline oxides to any greater extent than copper. (5) Freshly cut titanium solid phase welds to other metals in frictional contact. The degree of welding is independent of the atmosphere (air, nitrogen, or argon) or the time (less than 24 hours) at room temperature in such atmospheres. This behavior is contrary to that experienced with iron or copper With the latter couples less than five minutes exposure of a freshly cut surface to air is sufficient to markedly reduce the degree of solid phase welding. (6) The seizability of titanium is probably due to the lack of resistance, of the contaminant film formed on it in air, to penetration or wear in frictional contact.