Processing of metallic filaments

Metals can be given a fibrous form by a variety of techniques. The most common one is, of course, the technique of wire drawing. Wire drawing can be used to obtain filaments down to 100 xm diameter. In order to obtain metallic filaments smaller than this size, one must resort to unconventional techniques. We describe below some of these techniques. 

Most metals with FCC and BCC structures can be easily drawn into a wire or filamentary form. The process exploits the ability of metals to undergo large-scale plastic deformation. A schematic of the wire drawing process is shown in Fig. 5.2. The material is pulled through a conical die that forces a reduction in the diameter. Lubrication must be used to decrease the frictional forces. The entrance to the die is so shaped that the wire entering the die will also draw some 

This drawing efficiency is a function of the die angle, amount of deformation produced in a pass, lubrication, etc. In general, the value of t) varies between 0.5 and 0.65 (Hosford and Caddell, 1983). In terms of an average stress one can write for the total work done 

For many metals, the flow curve, i.e. the true stress versus true plastic strain curve, can be expressed as a power law. 

For a material obeying power law work hardening (Eq. (5.5)), it can be shown that 

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