Friction and Wear of Metals in Gases Up to 600 C

Abstract

Apparatus is described for measuring friction and wear in controlled atmospheres. A comparison is made of the room temperature behavior of copper, mild steel and brass, rubbed against a hardened tool steel, in four environments—vacuum (10⁻³ mm Hg), dry helium, dry carbon dioxide, and dry air. The effect of varying the water vapor content in air is also discussed. The initial selection of rubbing pairs for service at elevated temperatures is gaseous environments under unlubricated conditions, is based on their long-term resistance to corrosion and their ability to give low wear rates. In general, therefore, the materials must be hard. Several alloys having chromium contents of between 1% and 30%, and hardness values in the range 200–1000 vpn have been investigated. These included two low-chromium nitrided steels, a tungsten-chromium tool steel and a series of four Co-Cr-W alloys. Specific wear rates and friction coefficients varied markedly with temperature, and values in the ranges 10⁻¹³–10⁻⁸ cm³/cm kg and 0.1–0.8, respectively, were obtained in both dry carbon dioxide and dry helium. Lowest wear rates were observed with the nitrided steels. The diverse characteristics observed are discussed on the basis of current theories of adhesive wear.