Low-cycle fatigue of niobium |
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Authors: | J M Meininger J C Gibeling |
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Affiliation: | (1) Science and Engineering Laboratory, McClellan Air Force Base, 95652 Sacramento, CA;(2) Department of Mechanical, Aeronautical and Materials Engineering, University of California-Davis, 95616 Davis, CA |
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Abstract: | Commercially pure niobium (CPNb) and a niobium-1 pct zirconium (Nb-lZr) alloy were tested under low-cycle fatigue conditions
at plastic strain amplitudes in the range of 0.02 pct ≤Δεpl/2≤ 0.7 pct. At low temperatures, the cyclic deformation response of body-centered cubic (bcc) metals is strongly dependent
on strain rate. Thus, it was necessary to test at slow (2 x 10su-4 s-1) and fast (2 x 10-2 s-1) strain rates in order to fully characterize the cyclic deformation at ambient temperature. Only cyclic hardening was observed
for both metals under all testing conditions. As expected, higher cyclic stresses were recorded at the fast strain rate compared
to the slow strain rate. The Nb-lZr alloy was always stronger than CPNb, although both metals had the same cyclic life at
equal plastic strain amplitudes. Further, the strain rate had no effect on the cyclic life. At the fast strain rate, intergranular
cracking occurred, and a microplastic plateau was observed in the cyclic stress-strain (CSS) curve for CPNb. At the slow strain
rate, no definitely intergranular cracks were detected, and a microplastic plateau was not observed for CPNb. The results
of these experiments are interpreted in terms of the influence of strain rate and solute content on the relative mobilities
of edge and screw dislocations. |
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