Page 220 - Fiber Fracture
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STRENGTH AND FRACTURE OF METALLIC FILAMENTS 205
Fig. 18. Wedge-shaped fracture surfaces of well annealed 25 km diameter Au wires, left 1 h at 800"C, right
pulsed annealing 0.5 s at 600°C.
Fig. /Y. Wire and fracture surfaces of 25 Fm diameter Au wires. Left: as-drawn with smooth surface and
almost no elongation at rupture. Right: annealed at 300°C with rough surface indicating begin of strain
localization.
to submit wires that have to pass 20 to 40 dies to intermediate annealing treatments.
Such treatments are conveniently executed in between two dies in line with the drawing
process and may also serve to modify the mechanical properties of the final product.
Since wires move at a velocity of a few centimeters per second, annealing times
remain necessarily short and the temperature has to be adjusted in order to get the
desired result. Such short-pulsed annealing treatments also allow to study the annealing
kinetics over several time decades. Fig. 22 shows the tensile stress and Fig. 23 the
elongation at rupture for 25 mm diameter Au wires as a function of the annealing time at
different temperatures. Wires were heated by direct passage of an electrical current. The
temperature was determined from the known temperature dependence of the electrical
resistivity. The electrical resistance also served to adjust the current in order to maintain
the temperature constant. For details see Hausmann (1987).