Production of Ni-Si-B amorphous alloy wires by melt extraction and their thermal and mechanical properties

Amorphous Ni-Si-B and Ni-Cr-Fe-Si-B wires were produced in the diameter range 20 to 100 μm by a melt extraction method using a copper wheel with edge angles of 30 and 60 degrees. Wires without any concavity in the transverse cross section were prepared in the extraction condition where the circumferential velocity of the wheel and the feed velocity of the molten alloy were in the ranges 20 to 60 m/s and 0.5 to 2.0 mm/s, respectively. The resulting amorphous wires had good bend ductility in the diameter range below 80 μm for the Ni₇₅S₈B₁₇ alloy and below 60 μm for the Ni₇₈Si₈B₁₄ and Ni₆₈Cr₇Fe₃Si₈B₁₄ alloys. The thermal stability and hardness of the amorphous wires were nearly the same as for the melt-spun amorphous ribbons. The σ_f was 2810 MPa for the Ni₇₅Si₈B₁₇ wire, which is about 20 per cent higher than those for the corresponding ribbon samples because of the low degree of stress concentration resulting from good smoothness on the outer surface. No appreciable concavity resulting from the use of a copper wheel with a sharp edge was seen in the cross section and solidification is considered to have been completed during the flight after extraction. Thus, the formation of these amorphous alloy wires with a circular cross section for the Ni-Si-B alloy without a strong oxide-forming element is due to the rapid solidification of the fine supercooled liquid stream in the absence of heterogeneous nucleation during high-velocity flight in the argon atmosphere. The good formability into the wire shape for the Ni-based alloys without a high degree of shape stability in the molten state allows us to expect that the present process can develop as an alternative method to produce amorphous alloy wires in various alloy systems where an amorphous wire has not been prepared.