EFFECT OF PURITY AND TEMPERATURE OF DYNAMIC MICROSTRAIN OF NIOBIUM (CB)
Technical Report,01 Aug 1965,28 Feb 1967
AEROSPACE CORP EL SEGUNDO CA EL SEGUNDO
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An experimental technique was developed for a dynamic tensile stress-strain test in which plastic strain is measured continuously throughout the microstrain region extending through the macroflow region to total deformations of 5. The tests were carried out on Nb samples having interstitial impurity levels of 160 and approximately 800 ppm at temperatures ranging from room temperature down to 100K. A band spectrum of activation energies was obtained from calculations based on the measured activation volumes and temperature dependence of flow stress. The inability to predict such a phenomenon on the basis of a single rate-controlling process has led to the proposal that several sequential rate-controlling dislocation mechanisms are operative in the preyield microstrain region. These are thought to be the motion of geometrical kinks, the formation of double kinks in edges, and finally, in the macrostrain region, the formation of double kinks in screws. In less pure Nb the effect of interstitial impurities is shown to be dominant in the microstrain region a result which suggests that a fourth mechanism is overcoming interstitial barriers rather than the motion geometrical kinks and formation of double kinks in edge dislocations.