Stress reduction tests on Nb-1wt.%Zr at 1300 K

Abstract

The objective of this paper is to analyze the stress reduction behavior of b.c.c. Nb-1wt.%Zr at 1300 K (0.47 of the melting point T m). After small reductions in stress an increasing strain rate was observed, while after large stress reductions a decreasing strain rate was observed. The reduced strain rate normalized by the intial strain rate plotted semi-logarithmically as a function of the reduced stress normalized by the initial stress showed two branches ( i.e. a low and high stress sensitivity region) indicating that two different dislocations mechanisms are operating. From the high stress sensitivity branch a true activation area was calculated, which was in the range of the true activation area for cutting of forest dislocations. The normalized true activation area was found to be less than the empirically predicted dislocation spacing in the subgrain interior. Similar behavior was observed for aluminum and Al-5at.%Zn. Extrapolating the low stress sensitivity branch to σ/σ 0 equaling one shows that 10% of the total strain rate is owing to the dislocation mechanism operating at the low stress sensitivity region. The mechanism operating at the low stress sensitivity region was assumed to be subgrain boundary migration.