Hydrogen-induced accelerated grain growth in vanadium.

Grain growth in nanocrystalline vanadium films was studied at 600 and 700 °C in vacuum and in hydrogen atmosphere with partial pressures ranging from 1 to 1000 Pa. It is shown that grain growth is significantly increased in the presence of hydrogen. Thus the expected effect of retarding grain growth either by reducing grain boundary energy due to hydrogen segregation or by hydrogen drag on the moving boundary did not occur. Two explanations are given for the accelerated grain growth. First, hydrogen reduces the formation energy of ledges, assuming these ledges are required for initiating and advancing boundary motion. Second, grain growth requires the annihilation of excess volume which may be enhanced by reducing the formation energy of vacancies in the presence of hydrogen. [ABSTRACT FROM AUTHOR]