Compositional Effect on Crystallization of (Fe, Ni, Co)-Si-B Amorphous Alloys

Compositional effect on the structural changes during heating up to 700°C has been examined with a number of amorphous alloys of X-Si-B and (X, Y)78Si10B12 (X, Y: Fe, Ni, Co) by differential scanning calorie and Vickers hardness measurements, transmission electron microscopy and X-ray diffraction analysis.(1) The amorphous phase of X-Si-B alloys is obtained in the compositional range of 20 to 30 at% metalloid contents. The crystallization temperature of these amorphous alloys is low at low metalloid contents, but it increases with increasing metalloid content. The crystallization process changes in the vicinity of 27∼29 at% metalloid contents. Below and above this metalloid content, the amorphous alloys crystallize following the process of Am→Am+MS-I→MS-I+MS-II→Stable. In the lower metalloid contents the MS-I phase is a crystal with the same structure as each mother metal, while in the higher contents it is a compound containing a large amount of metalloid elements. At the intermediate metalloid content (27∼29 at%), these MS-I phases do not precipitate, but MS-II phase appears directly from the amorphous matrix and transforms finally to stable phases.(2) The crystallization process of amorphous (X, Y)78Si10B12 alloys proceeds through two metastable phases (MS-I and MS-II) and finally to stable phases. The crystalline structure of MS-I phase agrees well with that of equilibrium phase at room temperature for the X-Y binary alloys.