Features of structure and phase transformations in shape memory TiNi-based alloys after severe plastic deformation
2002; International Information and Engineering Technology Association; Volume: 27; Issue: 3 Linguagem: Inglês
ISSN
1958-5934
AutoresВ. Г. Пушин, V. V. Stolyarov, Р. З. Валиев, Н. И. Коуров, Н. Н. Куранова, Egor Prokofiev, L. I. Yurchenko,
Tópico(s)Silk-based biomaterials and applications
ResumoAbstract Amorphous and nanostructured TiNi-based alloys (Ti50Ni50, Ti49.5 Ni50.5, Ti50Ni49Fe1, in at.%) were first produced using two techniques of severe plastic deformation (SPD), namely high pressure torsion (HPT) and equal channel angular pressing (ECAP). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to examine the structural states and phase compositions of initial and SPD specimens, their thermostability on annealing and cooling, including in situ experiments. The nanocrystallization temperatures of the amorphous alloys and critical points of martensitic transformations in the crystalline alloys were also determined by means of measurements of the temperature dependence of electrical resistance. It was shown that martensitic transformations in the sequence B2↔R↔B19′ occur in nanostructured TiNi-based alloys or, on the contrary, only a single B2↔R transition can occur in the amorphous-nanocrystalline alloys. In nanostructured SPD-alloys cooled to below the Ms′ or Ms temperatures, nucleation and growth of R- and B19′-martensites occur by a “B2-austenite single nanocrystal — martensite single crystal” mechanism without microtwinning. Only in submicrocrystalline SPD-alloys with coarser B2-grains (larger than 100 – 200 nm) the R and B19′ martensites had a twinned packet morphology.
Referência(s)