Kraposhin

The authors established the influence of preliminary heat treatment (annealing at 950°C, 0.5 hrs, cooled with furnace + tempering at the interval of 500-700°C) on hardness of the nitrided layer of steel 38H2MYUA (nitriding at 500°C, 30 h). Similar results were obtained in a model of carbon-free alloy Fe-4% Cr. By the method of nuclear gamma resonance spectroscopy (the Mossbauer effect) on the model alloy it was established that Fe-Cr clusters are formed during the cooling process starting from 950°C and the subsequent tempering. Clustering affects the size and number of particles of chromium nitride formed during subsequent nitriding at 500°C. Depending on the heat treatment before nitriding, Fe-Cr clusters are characterized by different filling of chromium atoms of the first and second coordination spheres of iron. According to the Mössbauer spectra after annealing at 950°C and tempering at 550°C, during the following 10 hrs before nitriding in the structure of the solid solution clusters are formed, and they correspond to the crystalline structure of  the σ-phase Fe-Cr system: Frank-Kasper polyhedra with 14 vertices.

In the framework of the density functional theory ab initio calculations of free energy at 0 K, electron density and magnetic moments were performed for Pd-Mn and Cu-Mn spin glasses. It was assumed, clusters consisting of two, three or four Mn ions existed in solid solution thus forming dumbbells, triangles or tetrahedrons respectively. Clusters stabilize solid solutions in all cases, while the magnitude of the magnetic moment is dependent on the cluster structure. In Pd-Mn solutions the highest value of the giant magnetic moment per Mn ion (7,2 Bohr magnetons) corresponds to Mn tetrahedron with the sequences of Mn-Pd-Pd-Mn as the tetrahedron edges. In Cu-Mn solutions the highest value of the giant magnetic moment (4,2 Bohr magnetons) corresponds to a single Mn ion. It was established that fields of solid solutions in Pd-Mn and Cu-Mn systems corresponded to the states of the colloidal solid solution.

The authors show the existence of special polyhedra (clusters) and combinations of polyhedral, which are the structural implementation of algebraic geometry constructions. An algorithm of graph derivation corresponding to a special class of simple polyhedra with 24 vertices and 14 faces was considered for the case when these polyhedra have 4-, 5- and 6-gonal faces. The graph was derived for the first time for the polyhedron with one tetragonal face and which is not a parallelohedron. Polyhedra of this class allowed to determine the possibility for 14-verticed canonic and non-canonic Frank-Kasper polyhedra to be presented in the structure of intermetallics. This approach allowed to determine the symmetry of wide spectrum of ordered (not necessary crystalline ones) tetra-coordinated (diamond-like, clathrates) and tetrahedral (metallic) structures larger, including also nanostructured states.

The symmetry of a clathrate crystal can be adequately displayed within the apparatus based on constructions. The apparatus of algebraic geometry and topology was proposed for fundamental description of tetrahedral and tetra-coordinated structures. Such a description allows to represent any structure as a combination of helices (rods) consisting of polyhedrons i.e. cavities of clathrates or coordination polyhedrons of intermetallic semiconductors. The crystal lattice can arise only as a variant of such a combination. Crystal structures of clathrates (gas-hydrates and intermetallic semiconductors) are described as a combination of helicoids with nonintegral swivelling axes 10/3, 12/5 и 15/4. The structure of clathrate IX (Ba24Ge100) for the first time was determined as dual to the β-Mn structure.

A new model of carbon placement in the lattice of the austenite was proposed; it is based on the equality of diamond's and austenite's lattice periods. Carbon dissolves in austenite as a centered tetrahedron which is a fragment of diamond structure. Vertexes of carbon tetrahedron are placed in the austenite lattice sites, this way the fifth atom of carbon is in the center of carbon tetrahedron, without causing distortion in the austenite lattice. This model was proved with experimental data of nuclear gamma-ray spectroscopy and is consistent with the proposed single model of pearlite and martensitic austenite transformation as multi-doubling of austenite density.