Small-angle neutron scattering of precipitates in Ni-Ti shape memory alloys

Abstract Small-angle neutron scattering was performed on polycrystals of Ni–(46–49) at.% Ti quenched in ice water from the solid solution. The presence of small precipitates of a radius of about 1 nm was found for Ni–(46, 47 and 48) at.% Ti. Assuming a composition of Ni 4 Ti 3 of the precipitates, their volume fraction varies from 7% to 0.3%. No precipitates are found if the Ti content is closer to stoichiometric NiTi. The formation of these precipitates already during quenching seems to suppress the formation of martensite. Ni–(47.9 and 48.5) at.% Ti were further aged for 1 h at 553 K, and small-angle scattering shows a fully established precipitate microstructure. The particles have a radius of about 1.5 nm and a mean interparticle distance of 4.8–5.8 nm. From the integrated small-angle scattering curves, a volume fraction of Ni 4 Ti 3 particles of about 20% is obtained.