On the temperature dependence of the yield stress of niobium

Abstract

The effects of temperature on yield stress of niobium crystals showed that a change of slope occurs at approximately 175 deg K. Specimens tested below this temperature were examined for evidence of twinning, which was found to occur only occasionally at 77 deg K. When the nitrogen content of the specimens was increased to from 42 to 85 ppm, twinning was found to occur consistently at 77 deg K but not at 86 deg K. Hydrogen had the same effect when increased from 2 to 100 ppm. When the oxygen content was increased from 40 to 800 ppm, twinning was not observed at any temperature. Thus it appears that twinning is not highly dependent upon interstitial content. All three elements tended to decrease the temperature dependence of yield stress at temperatures above the anomalous region but did not produce any marked effect at lower temperatures. (P.C.H.)