The Effects of Interstitial Impurities on the Yielding Behaviour of Niobium Single Crystals

The effect of the overall impurity content on the yielding behaviour of niobium single crystals has been investigated in tension between 77 and 473 °K. In the 〈110〉 orientation the amount of yield drop depends on the impurity level of the crystal, and the temperature dependence of the yield stress was decreased significantly for both 〈110〉 and 〈100〉 orientations for purer crystals. Current theories of solution and lattice hardening were applied to try to account for the observed temperature dependence of the yield stress. Gilman's reaction rate theory is found to be the best explanation for the observed yielding behaviour. The twinning stress of 〈110〉 oriented single crystals in compression showed no systematic variation with impurity content when tested at 20.4 °K.