Tula State University, Tula, Russia:

G. V. Markova, Head of the Chair of Physics of Metals and Materials Science, e-mail: galv.mark@rambler.ru

S. S. Volodko, Post-Graduate Student of the Chair of Physics of Metals and Materials Science, e-mail: volodko.sv@yandex.ru
I. A. Alimov, Master’s Student of the Chair of Physics of Metals and Materials Science, e-mail: alimov.iwann@mail.ru

LLC Metsintez, Tula, Russia:

A. V. Kasimtsev, Director, e-mail: metsintez@yandex.ru

The authors studied the structure, a phase composition, mechanical and functional properties of a TiNi binary powder alloy (Ni = 55.5% (wt.)) after cross rolling at 900 ^oC with a degree of true strain of ε = 1.5. It is shown that after cross rolling at ε = 1.5 the structure contained R-martensite amounting to 5% or less. Due to lower rolling temperature, the dynamic recrystallization develops in some volume, and only a share of grains is in a polygonized and recrystallized state. The average grain size is d_av = 34±2 μm, which is significantly lower than after a preceding deformation stage (ε = 0.8, d_av = 64 ± 2 μm). Variations in a grain size occur in center and surface layers of rolled rods. However, such variations in a grain size do not influence microhardness across the sample section. As a result of the deformation at ε = 1.5, axial porosity decreases, entailing an increase in the alloy density up to 6.4 g/cm³. The decreased axial porosity and grain refinement contributed to an increase in ductility up to a required level (δ >10%). Thus, a set of mechanical properties of TiNi after cross rolling at a strain degree of ε = 1.5 satisfies requirements of specifications TU 1-809-394–84 for alloy grade TN1. It is shown that after rolling a TiNi powder alloy is characterized by its high damping capacity in a temperature range of a martensite transformation. When carrying out tests, this alloy in austenite state shows superelasticity, while during tests in martensite-austenite state — superelasticity and shape memory effect. The studies on the effect of preliminary torsional deformation on shape memory properties showed that the shape of wire samples was fully restored up to γ_tor = 14%, then an unrestored part of deformation occurs due to an unreversible sliding effect.

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