Plastic Deformation of <I>bcc</I> Metal Single Crystals at Very Low Temperatures

Single crystals of high-purity (RRR\simeq4000) niobium were tested in tension in the temperature range of 2 K–350 K to study the low temperature plasticity. Activation analyses of the results showed that an Arrhenius type strain-rate equation appeared to hold above 50 K but not below this temperature. Increase of the flow stress with the superconducting to normal transition by application of magnetic field changed almost linearly with decreasing temperature below the critical temperature (9.3 K).Experimental data of activation analyses below 70 K for four bcc metals, present Nb, previous Ta, Fe and β-CuZn (CsCl type), exhibit a common feature of discrepancy of the Arrhenius rate equation at very low temperatures. The mechanism of this discrepancy has been discussed in terms of quantum mechanical vibration of dislocations.

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