Ultralow friction behavior of borided steel surfaces after flash annealing

Abstract

In this letter, we describe the ultralow friction mechanism of borided steel surfaces subjected to a short-duration, or ''flash,'' annealing procedure. In this procedure, a borided steel surface is exposed to high temperature (600 to 800 degrees C) for a short time (3 to 5 min) and then cooled to room temperature in open air. During the high-temperature exposure, boron atoms within the borided layer diffuse to the surface and react spontaneously with oxygen in air. The reaction product is a thin boron oxide film. During cooling, the boron oxide reacts spontaneously with moisture in the surrounding air to form a thin boric acid film. The sliding friction coefficient of a Si3N4, ball against this flash-annealed surface is about 0.06, but is 0.5 and higher against the unborided or borided-only surfaces. Mechanistically, we propose that the ultralow friction behavior of the borided and flash-annealed surface is due mainly to the layered-crystal structure of the boric acid film that forms on the sliding surface. (C) 1996 American Institute of Physics.