Thermodynamic calculation and ion beam mixing experiments were carried out for five sets of multilayered films with compositions of Fe40Ta20(ZrxTi1-x)(40) (x=0, 0.25, 0.5, 0.75, 1). The results show that the experimental results agreed well with the prediction, i.e., unique amorphous phases could be formed in all the five sets of films, and by replacing Ti with appropriate amount of Zr, the glass forming ability of the alloy could be improved. Meanwhile, phase separation of amorphous phase was observed in the Fe40Ta20Zr40 and other quaternary films. The possible mechanism of the amorphous phase formation and separation was discussed based on thermodynamic calculation and atomic collision theory. (C) 2014 Elsevier B.V. All rights reserved.