LOW-TEMPERATURE INTERNAL FRICTION IN DEFORMED SINGLE CRYSTALS OF NIOBIUM AND NIOBIUM-MOLYBDENUM ALLOYS

The low‐temperature internal friction spectrum has been measured on single crystals of Nb and Nb‐Mo alloys deformed in tension. The α‐peak height is found to increase in proportion to the square of the work‐hardening stress and, therefore, in direct proportion to the dislocation density. The addition of interstitial impurities or substitutional molybdenum is found to increase the frequency factor of the α‐peak without changing the activation energy. The maximum peak height is decreased substantially both by impurities and by decreasing the deformation temperature. It is concluded that the α‐peak is similar to the Bordoni peak in f.c.c. metals and is due to either an intrinsic dislocation mechanism (most likely kink nucleation on non‐screw dislocations), which is sensitive to impurities, or an extrinsic mechanism in which impurities are more directly involved. Some preliminary observations on the β‐peak are also presented. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim