The results of the comparative analysis of the Ti 50 Ni 25 Cu 25 alloy structures produced in the initial amorphous state by rapid quenching from the melt (RQM), after severe plastic deformation by torsion under high pressure (HPT), and postdeformation heat treatment (PHT) are presented. The study was carried out using neutron and X ray diffraction, transmission and scanning electron microscopy, and measurements of electrical properties. The initially amorphous alloy has been established to nanocrystallize after torsion under a pressure of 7 GPa to 0.5 revolutions of the anvil. Then, after 1, 5, 10, and 15 rev, the alloy again undergoes the strain induced amorphization even with the retention, even after 5-15 rev, of a large number of highly dispersed nanocrystals less than 3-4 nm in size with a distorted B2 lattice in the amorphous matrix. Their crucial role as nuclei of crystallization provides the total low temperature nanocrystallization during subsequent annealing starting from 250-300°C. It is shown that PHT of the alloy amorphized by HPT makes it possible to produce extremely uniform nanocrystalline (NC), submicrocrystalline (SMC), or bimodal (NC + SMC) austenitic B2 type structures in it. A complete diagram of thermoelastic martensitic transformations in the region of B2 austenite states, from nanostructured state to conventional polycrystalline one, has been constructed. The size effect on the stabilization of martensitic transformation in nanocrystalline B2 alloy has been established.

No abstract

Results of investigations of structural and phase transformations that occur in the titanium nick elide based alloy Ti 49.5 Ni 50.5 with a shape memory effect during severe plastic deformation by torsion under high pressure (HPT) are reported. The studies were performed using transmission and scanning electron microscopy, neutron and X ray diffraction, and measurements of temperature dependences of electrical resistivity. The martensitic B2 → B19' transformation was found to be induced in the alloy when applying a high pressure. After unloading, the martensitic B19' phase is retained in the alloy. The fine structure of the B19' martensite and its evolution into nanocrystalline and, subsequently, amorphous state during HPT with 1/4, 1/2, 1, 5, and 10 rev have been studied. It was shown that, after HPT, all nanosized crystallites whose sizes are less than 30-50 nm have a B2 type structure and, therefore, the reverse martensitic B19' → B2 trans formation is realized in the alloy at room temperature after unloading.

No abstract

No abstract