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Nanoclusters in solid solutions of iron-chromium and their influence on hardness of the nitrided layer of steel 38H2MYUA
Engineering Education # 11, November 2012
DOI: 10.7463/1112.0496806
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.
77-30569/342193 Ab initio calculations of the electronic structure of Pd-Mn and Cu-Mn spin glasses: manganese clusters and a giant magnetic moment
Engineering Education # 03, March 2012
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.
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