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).
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