The critical thickness for the formation of Ni-Si-B amorphous alloys

• DOI: 10.1007/bf02643483
• Publication Date: 2007-06-10T05:53:51Z
• Authors: M. Hagiwara; A. Inoue; T. Masumoto
• Keywords: 0103 physical sciences; 01 natural sciences

In order to estimate the critical sample thickness for the formation of an amorphous phase, a new melt-spinning type quenching apparatus has been constructed which enables the roller revolving at high speeds, such as 5000 rpm, to stop in a very short time of 1 to 2 s. A long ribbon of Ni-Si-B alloy with a continuous variation in thickness in the range of about 30 to 300 μm has been produced in one ejective operation using this modified quenching apparatus. The critical thickness, taken as that thickness where we just observed a crystalline particle by optical microscopy at the magnification of 100 times, is the largest (225 μm) for Ni75Si8B17, decreases with increasing or decreasing silicon and boron contents and is about 30 to 40 μm near the boundary between amorphous and crystalline phases. Further, the effect of ribbon thickness on crystallization temperature, the heat of crystallization, the activation energy for crystallization, hardness and ductility has been examined and it has been demonstrated that the disordered state differs with cooling rate even in an amorphous alloy with the same alloy composition.