Abstract The ion beam assisted deposition (IBAD) technique is utilized to study amorphization in Fe–Nb binary metal systems. The amorphous range covers a Nb fraction of approximately 34–60 at.%. The Fe-rich and Nb-rich supersaturated solid solutions of the bcc phase were obtained in Fe 66Nb 34 and Fe 31Nb 69 films, respectively. In the Fe 66Nb 34 films, the ‘amorphous→amorphous+bcc→bcc’ evolution with increased ion beam energy from 2 to 8 keV is observed accompanying changes of film morphology. The phase formation in the IBAD process is determined by both thermodynamic and kinetic factors.