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

Abstract

Bulk glassy Fe73Al5Ga2P11C5B4 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, Fe3(B, C), Fe2B and Fe3P phases for the 1.5 mmφ sample and coexistent Fe3(B, C), Fe2B and Fe3P phases for the 2.0 mmφ 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 (Tg), crystallization temperature (Tx) and heat of crystallization of the 1.0 mmφ 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 mmφ glassy alloy has ferromagnetism with a Curie temperature of 606 K and exhibits 1.26 T for saturation magnetization (Bs), 82 A/m for coercivity (Hc) and 0.38 for the ratio of residual magnetization to Bs at room temperature. The large ΔTx(=Tx−Tg) 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.