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Proceedings Paper

Cluster model of amorphized particles formation by plasma spraying of metallic powder
Author(s): Boris K. Barakhtin; E. V. Nesterova
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Paper Abstract

Multifunctional coatings from materials with amorphized microcrystalline or nano-phase structure cause a considerable scientific and practical interest. With their help it is to manufacture heat resistant neutralizers of harmful ejections, to produce ecologically clean sources of electric current, to design electromagnetic protective shields and to fabricate a lot of other technical products. The variety of application and a unique complex of operating characteristics (ductility, strength, magnetic and chemical properties) are governed by the basic peculiarity of material in amorphized state -- its thermodynamic instability. In comparison with traditional thermodynamically equilibrium metallic alloys, the kinetics of structure changes in amorphous materials is quite different. Thus, it is suggested, that they have peculiar defects (phasonics) which are not typical of materials in crystalline state, they have no translational symmetry and elementary cells. In the process of coatings forming with non-equilibrium structure states can be realized in them, which are characterized by a fluctuation type of origin, entropy export, appearance of space or temporary symmetry uncertainty of the transition direction 'order $ARLR disorder' in bifurcation points. The aforesaid explains a great scientific (not only practical) interest in the structure study of disordered medium. Functional coatings with amorphized, nano- and microcrystalline structure components formed on copper substrate by plasma spraying of dispersed (to 50 mcm) Ni-Al powder. According to the constitutional diagram it was expected to obtain a mixture from equilibrium intermetallide phases NiAl3 + Ni2Al3. The experimental results and investigations performed by X-ray structure, X-ray spectrum and electron microscopy techniques have shown it is possible to obtain phases of variable composition (Ni)m(Al)n with Ni content from 25 to 75 vol.%, including NiAl. It turned out that in the process of spraying the dispersed particles of the size 3 - 70 mcm were generating at the coating surface, which differed significantly in morphology, crystallinity degree and chemical composition. Thus, equiaxial and scaly particles stand out in their morphologic characteristics among particles. Scales are fixed as isolated aggregates on the whole coating, including the surface of equiaxial formations. It has been determined the internal structure of thin scales is amorphous of they contain above 50 vol.% Ni. This fact is illustrated by a typical diffusion halo around the central reflex in microdiffractional picture. Massive scales and equiaxial particles are classified as nano- and microcrystalline objects of variable chemical composition. On the basis of the obtained experimental data it is possible to state that the amorphized state can be detected with a high probability in particles containing above 50 vol.% Ni, having a scaly appearance and relief contour with a fractional space dimensionality. The latter agrees with the principle of the existence of a close correlation between stoichiometry and geometrical peculiarities of the phase solidified. The experimental results were used as the base of formation process model for amorphized particles.

Paper Details

Date Published: 5 May 1999
PDF: 4 pages
Proc. SPIE 3687, International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering, (5 May 1999); doi: 10.1117/12.347441
Show Author Affiliations
Boris K. Barakhtin, CRISM Prometey (Russia)
E. V. Nesterova, CRISM Prometey (Russia)

Published in SPIE Proceedings Vol. 3687:
International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering
Alexander I. Melker, Editor(s)

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