Thermal stability and magnetic properties of bulk amorphous Fe-Al-Ga-P-C-B-Si alloys

The effect of Si additions on the thermal stability of the supercooled liquid before crystallization, glass-forming ability (GFA) and soft magnetic properties was examined for amorphous alloy series Fe72-xAl5Ga2P11C6B4Si2, Fe72Al5-xGa2P11C6B4Six, Fe72Al5Ga2P11-xC6B4Six and Fe72Al5Ga2P11C6-xB4Sx. The increases in the thermal stability and GFA and the improvement of soft magnetic properties were recognized in the replacements of P by 1 to 2 at%Si and of C by 1 at%Si. The supercooled liquid region (Delta T-x) defined by the difference between crystallization temperature (T-x) and glass transition temperature (T-g) increases from 53 K for Fe72Al5Ga2P11C6B4 to 58 K for Fe72Al5Ga2P11C5B4Si1. The maximum thickness for glass formation (t(max)) by copper mold casting increases from 1 mm for the Fe-Al-Ga-P-C-B alloy to 2 mm for the Fe72Al5Ga2P10C6B4Si1 alloy. The increases in Delta T-x and t(max) are presumably because of the increase in the degree of the satisfaction of the three empirical rules for the achievement of large glass-forming ability, i.e., (1) multicomponent alloy systems consisting of more than three elements, (2) significantly different atomic size ratios above about 12% and (3) negative heats of mixing. The soft magnetic properties are also improved by the replacement of 1 at%Si for P or C through the increase in the squareness ratio of B-H loop (B-r/B-s) and the decrease in coercive force (H-c). The best soft magnetic properties for the bulk amorphous alloys are obtained for the Fe72Al5Ga2P10C6B4Si1 alloy and the saturation magnetization (B-s), H-c, B-r/B-s, and Curie temperature are 1.14 T, 1.5 A/m, 0.45 and 594 K, respectively. The success of forming the Fe-based bulk amorphous alloys of 2 mm in thickness exhibiting the good soft magnetic properties is promising for future development as a new type of soft magnetic material.