Effect of disorder on the martensitic phase transformation in Nb3Sn

Specimens of Nb3Sn tape have been irradiated at approx.380 K with reactor-spectrum neutrons to fluences of 1.3 x 1019 n/cm2 (E>1 MeV) and the internal friction and dynamic Young's modulus measured from 6 to 300 K. The softening of the lattice with decreasing temperature is seen to decrease from 40% of the room-temperature value at 10 K for unirradiated Nb3Sn to 94% at a fluence of 1.3 x 1019 n/cm2. The internal friction delta due to tetragonal domain-wall motion of the transformed material decreased with increasing fluence, being completely suppressed after approx.4 x 1018 n/cm2. The transformation temperature T/sub m/ decreased from approx.49 K for the virgin specimen to 22 K for a fluence of 3.8 x 1018 n/cm2 with no evidence of any tetragonal transformation at all for higher fluences. The lattice-dynamical and electronic changes responsible for these effects are not known at this time, but are seen to be correlated with the neutron-induced disorder