INTERNAL FRICTION AND YOUNG'S MODULUS OF Nb₃Sn BETWEEN 6 AND 300 K

Abstract
Young's modulus and internal friction were measured in polycrystalline NB₃Sn between 6 and 300K. Below the martensitic transformation temperature a large rise in internal friction is observed, in agreement with recent observations. In this temperature range, the internal friction is found to be nearly independent of frequency, a behavior consistent with stress-induced wall motion between domains of the tetragonal phase as the main source of relaxation. Internal friction peaks observed at 140 and 260K in Nb/Nb₃Sn composite tapes are tentatively attributed respectively to an α peak in Nb and hydrogen in the Nb₃Sn layer. Annealing at 750 °C for 1/2h is found to decrease the transformation temperature from 49 to 40K, and to modify the softening of Young's modulus in this temperature range. Young's modulus at 6K is 46% of room temperature value and is unchanged by the annealing treatment.