Thermal and Magnetic Properties of Bulk Fe-Based Glassy Alloys Prepared by Copper Mold Casting

摘要

Bulk glassy Fe_(73) Al_5Ga_2P_(11)C_5B_4 alloys in cylindrical form with diameters of 0.5 and 1,0 mm were found to form by a copper mold casting method. The further increase in diameter causes the formation of coexistent glassy, Fe_3(B, C), Fe_2B and Fe_3P phases for the 1.5 mm sample and coexistent Fe_3(B, C), Fe_2B and Fe_3P phases for the 2.0 mm* sample. It is to be noticed that the maximum thickness for glass formation is about 10 times larger than the largest thickness for Fe-based glassy alloys reported up to date. The glass transition temperature (T_g), crystallization temperature (T_x) and heat of crystallization of the 1.0 mm glassy alloy are 732 K, 785 K and 3.76 kJ/mol, respectively. No appreciable difference in the thermal stability and magnetic properties is seen between the bulk glassy alloys and the melt-spun ribbon. The 1.0 mm glassy alloy has ferromagnetism with a Curie temperature of 606 K and exhibits 1.26 T for saturation magnetization (B_s), 82 A/m for coercivity (Hc) and 0.38 for the ratio of residual magnetization to B_s at room temperature. The large triangle openT_X(= Tx - T%) and large glass-forming ability can be obtained for the Fe-based alloy containing simultaneously the five solute elements. The effectiveness of the multiplication is presumably due to the combination of the following three effects; (1) the suppression of crystalline nuclei due to the increase in dense random packing density for the glassy structure containing P, C and B with significantly different atomic sizes, (2) the difficulty of atomic rearrangements for the precipitation of the Fe-metalloid compounds caused by the generation of Al-metalloid pairs with strongly attractive bonding nature, and (3) the decrease in the preferential precipitation tendency of Fe-B and Fe-C compounds by the dissolution of Ga which is immiscible to B and C and soluble to Fe.