Page 212 - Fiber Fracture

STRENGTH AND FRACTURE OF METALLIC FILAMENTS 197

Fig. 11. The surfaces and edges of 600 p,m wide Fe75B15Si10 ribbon produced on a Cu wheel. The lower
half shows the side that was in contact with the wheel and the upper half the side that was in contact with
the air. The diameter of the crucible orifice was 0.45 mm and the pressure needed to eject the liquid alloy
was 0.4 x lo5 Pa. The Cu-wheel of 300 mm diameter turned with 1200 rpm.

water-quenched wires show values that are characteristic for the intrinsic behavior of
glassy metals. Rather good surface and edge qualities are also observed for very small
and thin ribbons. Such fibrous products can easily be produced on a wheel in air by just
using small nozzles. Minimal dimensions of about 100 km width and a thickness of 20
km can be reasonably achieved. For smaller dimensions the pressure needed to eject the
liquid metal strongly increases.
Figs. 11 and 12 show the surfaces and edges of a 600 pm and a 120 wm wide
Fe75B15Si10 ribbon melt spun on a Cu wheel and Fig. 13 shows the cross-section for
small ribbons. The irregular edges are clearly visible in the upper half of Fig. 11 (air side
of ribbon) and the air inclusions in the lower half (wheel side of ribbon). For the smaller
ribbons (Fig. 12) the surface tension becomes more important. It rounds and smoothens
the surface on the air side (Fig. 13), whereas the smaller width allows the air drawn
with the wheel to flow around the liquid droplet. The surface of the small ribbon (lower
half of Fig. 12) shows essentially a replica of the Cu-wheel surface. Fig. 14 shows the
quantitative surface profiles of the two ribbons shown in Figs. 11 and 12. Here again it
becomes evident that the impressions produced by the air inclusions penetrate more than
5 pm into the interior. This amounts to not less than 10 to 20% of the total thickness.
Since also the thin ribbons are not entirely free of edge defects it is important
to know whether they act as notches that affect their tensile strength. Fig. 15 shows
measurements of the tensile strength as a function of the notch depth on 160 pm wide
ribbons. The smallest notches were naturally present, whereas the larger ones were