Search

The paper studies the regularities of the spatial distribution of Ti3Ni4 particles in the inhomogeneous grain-subgrain structure of the nanocrystalline Ti-50.9 at. % Ni alloy depending on the aging temperature. It was found that the presence of different types of internal boundaries influences the inhomogeneous precipitation of coherent Ti3Ni4 particles in the temperature range of their intense precipitation at 400°C. Ti3Ni4 precipitate in the substructure around the low-angle subgrain boundaries, while the decomposition of the B2-solid solution is suppressed in nanograins with high-angle boundaries. It is proposed that the difference in the Ni concentration in the B2-austenite in the regions of the substructure and nanograins is the main reason for the implementation of the anomalous effect of the R-phase transformation B2↔R1,R2 in the martensitic transformation sequence B2↔R↔B19'. [ABSTRACT FROM AUTHOR]

In this work, we study the effect of annealing at temperatures of 300–500°C on martensitic transformations, structure, and deformation response of a NiTinanocrystalline alloy with a high nickel content using mechanical load/unload experiments. It is shown that the specific features of Ti3Ni4 precipitation, such as a change in particle size and their distribution in the nanostructure from location on dislocations to precipitates at subboundaries, is accompanied by a shift in martensitic transformation temperatures, leading to the appearance of the R-phase and providing a change in mechanical responses from pseudoelastic to shape memory. [ABSTRACT FROM AUTHOR]

We investigate the effect of heat treatments of nanocristalline Ni-rich NiTi alloy on the precipitation of Ti3Ni4 phase in the alloys grain/subgrain structure after annealing at 300°C and at 400°C, as well as on martensitic transformations and inelastic behavior. It is shown that the increase in Ti3Ni4 precipitate size and change in their distribution in the substrucrure is accompanied by a shift of martensitic transformation temperatures, leading to the occurrence of the R-phase, and ensuring change of mechanical responses from pseudoelastic to shape memory. [ABSTRACT FROM AUTHOR]

The structure of a nanocrystalline Ti−50.9 at. % Ni alloy with mixed subgrain/nanograin structure is investigated by transmission electron microscopy after annealing at temperature 400°C. The size, morphology and distribution of Ti3Ni4 particles formed in the process of the decomposition of a TiNi B2 solid solution are investigated. It is shown that the Ti3Ni4 particles precipitate in the substructure in the low-angle boundaries regions. The precipitation of coherent particles in subgrains is possible with the latter sizes less than 100 nm. At the same time, precipitations of Ti3Ni4 particles are not observed inside the nanograins. [ABSTRACT FROM AUTHOR]

The study was carried on for the single NiTi crystals subjected to the Si-ion beam implantation. Using the transmission electron microscopy technique (TEM), the surface layer structure [111]B2 was examined for the treated material. The modified near-surface sublayers were found to have different composition. Thus the uppermost sublayer contained mostly oxides; the lower-lying modified sublayer material was in an amorphous state and the thin underlying sublayer had a defect structure. [ABSTRACT FROM AUTHOR]

The study was carried on for the implanted single TiNi crystal containing misoriented localized shear mesobands in its near-surface layer [001] B2. Due to the response of material to the Si ion implantation treatment of the single TiNi crystal, deformation mesobands would form in its near-surface layer. Specially designed software tools were employed for the treatment of experimental data obtained from X-ray and electron diffraction patterns. The 3D crystallographic orientations were calculated for the localized shear regions, which were displaced relative to one another and with respect to the original monocrystal orientation. [ABSTRACT FROM AUTHOR]

A multilevel approach was developed to the experimental study of plastic deformation in anisotropic polycrystalline materials, using by way of an example HCP-Zr alloys. This allowed establishing the relationship and hierarchy of processes occurring at macro-, meso- and microscale levels in conditions of significant heterogeneity of plastic flow and of texture formation. [ABSTRACT FROM AUTHOR]