Ion beam modification of MoS x films on metals

Abstract

Solid lubricants (MoS x) on metal surfaces can be either sputtered films or burnished powder films. Ion beam modifications of sputtered MoS x films has resulted in a considerable improvement of the sliding life of the lubricating film. In the present paper, we discuss the structural and geometrical changes of sputtered MoS x films exposed to inert gas ion beams in the hundred of kiloelectronvolts range and with doses varying from 10 15 to 10 16 ions cm −2. The friction coefficient of sputtered MoS x films in a dry nitrogen atmosphere was measured to be approximately 0.04 both prior to and after ion bombardment, but the sliding life increased by a factor of 5. For lubricating purposes, MoS 2 is frequently used in powder form, and the adhesion to metal surfaces is then of crucial importance. In the present paper, we report two new approaches with the purpose of obtaining low friction metal surfaces. In the first approach, molybdenum is immersed as anode in a non-aqueous sulphide-containing solution. Although in principle similar to anodic oxidation processes, the molybdenum disulphide film formation on the surface is due to an electrophoretic deposition of colloidal MoS 2 particles. Ion bombardment of such a film with inert gas ions at hundreds of kiloelectronvolts sìnters the lubricating film, which has a friction coefficient of about 0.04 in a dry nitrogen atmosphere or equivalent to sputtered films. As a second novel approach to decreasing the surface friction of a molybdenum surface, 50–400 keV ion beams of sulphur have been implanted in molybdenum and characterized by Rutherford backscattering as well as tested with a reciprocal ball tribometer.