IRON-BASED BULK METALLIC GLASSES-OPTIMIZATION OF CASTING

In this paper, the iron-based alloy was studied that is perspective for preparation of bulk metallic glass. The nominal composition of investigated material is given by the formula Fe(56)Co(7)Zr(10)Mo(5)W(2)B(15). Two casting techniques were applied: (i) conventional casting into a copper mould in the induction furnace and (ii) casting in the arc furnace in the copper mould. In the first case, the diameter of the ingot was about 11 mm. In the second case, the special two-parts copper moulds differing in diameters of the casting inlet hole (3 and 1 mm, respectively) were used. The microstructure of alloys prepared by both techniques was studied using the light optical microscopy, SEM (Scanning Electron Microscopy) and XRD (X-ray diffraction). The material prepared by the first technique (conventional mould casting) shows polycrystalline microstructure with very fine crystallites in the amorphous matrix. The samples prepared by the second technique had a needle-like form - the diameter of ingots was given by the diameter of the inlet-casting hole. When the mould inlet hole 3 mm in diameter was used, the material had similar microstructure as that prepared by the convention casting in the induction furnace. Arc melting using the mould inlet hole 1 mm in diameter, however, led to a structure with very low number of fine crystallites. The X-ray spectrum taken in the latter case have shown several peaks revealing certain amount of (sic)-Fe and crystallized Fe(x)Mo(y) solid solution.