Positive effect of hydrogen-induced vacancies on mechanical alloying of Fe and Al

• Fe82Al18 nano-powders were prepared by ball milling and mechanical alloying.
• Full mechanical alloying of Fe–Al was achieved using hydrogen atmosphere.
• Hydrogen segregating at vacancies enhances vacancy concentration in Fe–Al.
• Hydrogen-induced vacancies facilitate diffusion of Al atoms into Fe grains.
• Nitrogen inhibits Fe–Al alloying by formation of a nitride layer on Fe grains.

Nanocrystalline Fe82Al18 powders were prepared by high energy ball milling in various atmospheres. Two preparation techniques were compared: (i) mechanical milling of pre-alloyed Fe82Al18 pieces and (ii) mechanical alloying of pure Fe and Al powders. Single phase Fe82Al18 nano-powder was formed by mechanical alloying in H2 atmosphere while milling in N2 or air environment suppressed mechanical alloying due to passivation of Fe surfaces. Positron annihilation spectroscopy revealed that mechanical alloying of Fe and Al in H2 atmosphere is mediated by hydrogen-induced vacancies.