Effect of disorder on the martensitic phase transformation in Nb3Sn

Abstract

Specimens of Nb3Sn tape have been irradiated at ∼380 K with reactor-spectrum neutrons to fluences of 1.3×1019 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 1.3×1019 n/cm2. The internal friction δ due to tetragonal domain-wall motion of the transformed material decreased with increasing fluence, being completely suppressed after ∼4×1018 n/cm2. The transformation temperature Tm decreased from ∼49 K for the virgin specimen to 22 K for a fluence of 3.8×1018 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.

Analysis of the strain dependence of the superconducting critical properties of single-crystal and polycrystalline Nb3Sn

“…In the presence of a pre-compressed strain of ∼2%, the Young's modulus at 4.2 K is found to increase by ∼45% [56]. Moreover, the neutron fluence strongly affects the Young's modulus: the higher the neutron fluence, the higher the Young's modulus, and the lower the T c and T M [83].…”

Martensitic phase transformation in A15 and Laves-phase compounds studied by internal friction

“…Indeed, the small amount of modulus softening in V,Ga and Nb,Ge (compared with Nb,Sn) suggests a smaller softening driving force for a transformation. When the total softening of Nb,Sn at 10 K has, by any treatment, been reduced from 40% of the room-temperature value to only 85% (the value of the present V,Ga material), all evidence of the martensitic transformation in the Nb,Sn disappeared (Snead, Kumakura and Suenaga 1983). This was caused by the decreased long-range order in the specimen.…”

“…As the martensitic phase transformation in Nb,Sn had disappeared when the order was reduced to this level (Snead et al 1983) and its T, value had been reduced from 18.1 to about 16 K, the absence of domain-wall internal friction in the Nb,Ge may be taken as evidence that the present specimen is non-transforming. The question on Nb,Ge now is, if specimens with a higher order parameter are investigated, will a transformation be in evidence?…”

“…More recently it has been shown that a large internal-friction feature is associated with the transformed, tetragonal domains in Nb,Sn. In particular, the internal friction increases with decreasing temperature below the transformation temperature T, as the square of the tetragonality [l -(c/a)]' (Bussiere, Faucher, Snead and Welch 1981) and is caused by stress-induced domain-wall motion; the modulus and the height of the feature is reduced by internal strain, but T, is unaffected (Bussilre et al 1981); alloying with a third elements decreases the magnitude of the internal friction with increasing concentration, but only reduces T, in some cases, probably depending on the preferential site occupation of the alloy (Bussicre, Faucher, Snead and Suenaga 1982); and that neutron-induced disorder reduces both the internal friction and the T, (Snead, Kumakura and Suenaga 1983). The internal friction due to the tetragonal-material domain-wall motion in transformed Nb,Sn showed an increase of almost three orders of magnitude above background in these later studies, providing a very sensitive means of studying the effects of various parameters on the martensitic transformation.…”