Hydrogen Effects in Refractory Metals

Abstract

The effects of hydrogen on the refractory metals molybdenum, tungsten, columbium, and tantalum are reviewed. Solubility, permeability, and diffusion of hydrogen in the refractory metals, refractory metal-hydrogen phase diagrams, and the effects of absorbed hydrogen and hydrogen environments on mechanical properties are covered. Molybdenum and tungsten have very low solubilities for hydrogen and are essentially unaffected by hydrogen. Columbium and tantalum can absorb large quantities of hydrogen and form hydrides, and are greatly embrittled by relatively small amounts of hydrogen at low temperatures. However, the solubility of hydrogen in columbium and tantalum decreases to low values above approximately l600 F (870 C), the hydrides are stable only at relatively low temperatures, and relatively large quantities of hydrogen are required to cause embrittlement at elevated temperatures. Embrittlement of columbium and tantalum by hydrogen at room temperature and below is usually associated with hydride formation. No investigations have been made of the mechanism of embrittlement by hydrogen at higher temperatures. Columbium and tantalum specimens will fragment when cooled from elevated temperatures in hydrogen or, under certain conditions, when exposed to hydrogen at room temperature.