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 Fe_72-xAl₅Ga₂P₁₁C₆B ₄Si_x, Fe₇₂Al_5-xGa₂P₁₁C₆B ₄Si_x, Fe₇₂Al₅Ga₂P_11-xC₆B ₄Si_x and Fe₇₂Al₅Ga₂P_11-xC_6-xB ₄Si_x. 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 (ΔT_x) defined by the difference between crystallization temperature (T_x) and glass transition temperature (T_g) increases from 53 K for Fe₇₂Al₅Ga₂P₁₁C₆B ₄ to 58 K for Fe₇₂Al₅Ga₂P₁₁C₅B ₄Si₁. 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 Fe₇₂Al₅Ga₂P₁₀C₆B ₄Si₁ alloy. The increases in ΔT_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 Fe₇₂Al₃Ga₂P₁₀C₆B ₄Si₁ alloy and the saturation magnetization (B_s), H_c, B_r/B_s, and Curie temperature are 1.14T, 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.