Structural and phase transformations in quasi-binary TiNi–TiCu alloys with thermomechanical shape-memory effects

Abstract

The structure, thermoelastic martensitic transformations, and physical properties of the usual microcrystalline and rapidly quenched submicrocrystalline ternary alloys of the quasi-binary TiNi–TiCu section with a copper content to 35 at % have been studied in a wide temperature range. The fine structure of the alloys has been investigated by the methods of the analytical transmission and scanning electron microscopy, and selected-area electron diffraction, including the in situ heating and cooling in the column of the microscope. The main specific features of the premartensitic state of the B2 austenite, the morphology, and the fine structure of the B19 and B19′ martensitic phases have been established, and their evolution upon the alloying with copper and upon grain refinement and cooling and heating in situ have been studied. According to the data of the temperature measurements of electrical resistance, magnetic susceptibility, and XRD analysis, generalized complete diagrams of the B2 ↔ B19′, B2 ↔ B19 ↔ B19′ and B2↔ B19 martensitic transformations that occur upon cooling in these alloys with an increase in the copper concentration in the limits of 0–8, 8–15, and 15–35 at %, respectively, have been constructed.