Effect of hydrogen on the coefficient of friction of iron

Abstract

The friction force of an Annco iron-on-Annco iron sliding system was measured in laboratory air, nitrogen, and hydrogen. The coefficient of friction for each environment was calculated and the amplitude of the "stick-slip" behavior from each environment was observed. It was found that the coefficient of friction obtained in the hydrogen environment was significantly smaller than the values obtained in laboratory air and nitrogen. Also, the amplitude of the "stick-slip" behavior observed in a hydrogen environment was less than that obtained in laboratory air and nitrogen.

These results were attributed to a decrease in the fracture strength of the Annco iron along the interface between the pin and the disk which was caused by the presence of gaseous hydrogen. The surface energy and decohesion models for hydrogen embrittlement, both mechanisms which explain brittle behavior, were considered valid in this test. The localized plasticity model of hydrogen embrittlement was considered invalid in this test.

Copper, a noble metal not susceptible to hydrogen embrittlement, was also used in friction tests. Tests conducted with copper-on-copper sliding systems showed no statistical difference between the coefficient of friction and the amplitude of the "stick-slip" behavior as the gaseous environment was varied between laboratory air, nitrogen, and hydrogen.

Finally, recommendations for further study and testing were presented. The recommendations included changing the gaseous hydrogen pressure to both high and vacuum levels, raising the temperature of the hydrogen gas, and using anyone of the great number of iron-based alloys susceptible to hydrogen embrittlement.