The Friction and Wear Behavior of Molybdenum-Tungsten-Chromium Alloys in High-Temperature Sodium Environments

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Abstract
Friction and wear data, obtained with a crossed-cylinders apparatus, are presented for a selection of molybdenum-tungsten-chromium alloys, over the temperature range 200–500 C, for two sodium environments: the molten metal, containing approximately 5 ppm of oxygen impurity, and pure argon containing sodium vapor at concentrations corresponding with the temperature equilibrium value. Some comparisons are made with results obtained in gaseous environments of pure argon, helium, and carbon dioxide. An indication is given of the effect on friction and wear behavior of increasing the oxygen content in liquid sodium from about 5 to 80 ppm. It was concluded that chemisorbed double-oxide films, formed by reaction of the molybdenum, tungsten, and chromium constituents of the alloys with the sodium environment, play a significant role in providing boundary lubrication in high-temperature sodium. Also that the effectiveness of the lubrication provided by such films is a junction of the specific nature of the sodium environment (vapor or molten state), and temperature, as well as time at temperature.

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