Page 255 - Fiber Fracture

238 H.U. Kunzi

the Fe75SiloBls wire, which is attained near lo6 cycles, increases from 0.25% to 1%
when the relative air humidity decreases from 85% to 35%. This shows once again
that fatigue often depends strongly on the chemical composition of the environment.
They supposed that the premature failure was caused by hydrogen that was dissociated
from the moisture and diffused into the wire. Hydrogen is known to provoke a severe
embrittlement also in amorphous metals. Subsequent measurement of wires where, in
order to improve the corrosion resistance, Fe was partially substituted with Cr gave a
substantial increase in the endurance limit. For the FeMCrl I Si1OBIS ribbon the fatigue
limit at 65% R.H. is 1.31% bending strain, that is about 4 times higher than for the
Cr-free wire and 3.3 higher than the crystalline piano wire. Multiplication of this strain
with the known elastic modulus for the Cr-free alloy (150 GPa) gives a stress endurance
limit of almost 2 GPa as shown in Fig. 49.

ACKNOWLEDGEMENTS
I would like to thank my colleagues and former collaborators Karin Busch-Lauper,
Karlheinz Hausmann, Richard Hofbeck, Nicklaus Baltzer, Moshe Judelewicz and Erwin
Tiirok who through their work greatly contributed to this review. I also express my
profound gratitude to Prof. Berhard Ilschner who accompanied these studies with
enthusiasm and interest as well as to Chris San Marchi whose critical discussions and
remarks during the preparation of this review were very helpful. Financial support from
Swiss National Science Foundation who supported several projects in this field as well
as the grant offered by Degussa (Germany) are gratefully acknowledged.

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