Formation of cluster aggregates with pentagonal symmetry in plastically deformed samples Ni51Ti49

The research of features of structural and phase transformations in alloys with shape memory effect Ni51Ti49, occur- ring during plastic deformation is relevant in connection with the extensive use of alloys of nickel-titanium systems in the manufacture of various products of rocket-space and aviation technology. The problem of structure in NiTi during plastic deformation is the subject of a lot of debates and needs further research. The aim is to study the microstructure of lenticular crystals, appearing as a result of plastic deformation Ni51Ti49 samples. Heat-treated alloy samples Ni51Ti49 were static stretched before breaking. The stretched samples were thinned at the neck region and prepared through ion etching for study by transmission electron microscopy. The lenticular crystals with numerous extinction contours were detected. In the electron diffraction patterns from crystals of lenticular system reflexes found appropriate phase with pentagonal symmetry axis. As a result of the decryp- tion of the diffraction pattern revealed B2 matrix phase with parameter 3.01 Å, phase fcc with parameter 3.68 Å, as well as a system of reflexes of the primitive cubic lattice with a parameter of 2.13 Å. Based on the review performed by the modular representation of the crystal structures of the scheme of formation of the cluster unit with pentagonal symmetry, can explain the experimental results. BCC lattice can be described as a system consisting of 6 wrong octahedra. FCC lattice can be represented as a combination of a regular octahedron surrounded by a regular tetrahedron, linked by common triangular faces. The ten reflexes of phase with pentagonal symmetry correspond to d111 = 2.13Å FCC lattice. 20 tetrahedrons from FCC lattice are forming an icosahedron due to small displacements of atoms It is demonstrated how icosahedral phase with pentagonal symmetry formed from tetrahedral simplices FCC lattice can be inscribed in a simple cube with the appropriate parameters. Theoretical information on features of the diffraction methods of the structure investigation was considered, which allowed describing the observed diffraction patterns, as well as linking them with the theoretical concepts proposed in the framework of the cluster model.