Journal of Physical Studies 22(3), Article 3702 [5 pages] (2018) DOI: https://doi.org/10.30970/jps.22.3702 CONTROLLED NANOSTRUCTURING FROM AN AMORPHOUS STATE IN MULTICOMPONENTAL ALLOYS BASED ON COBALT V. I. Lysov, T. L. Tsaregradskaya, A. M. Kurylyuk, O. V. Turkov, G. V. Saenko Kyiv Taras Shevchenko National University, 64, Volodymyrska St., UA-01033, Kyiv, Ukraine

Using amorphous materials in current nanotechnology allows us to obtain characteristics that could not be produced by using materials with crystalline structure. The metastable amorphous state obtained by ultrafast quenching does not always have the best characteristics, however, methods of controlled nanostructuring is now an important area of metallic glass research. The great attention to the processing (heat and pressure treatment) of amorphous alloys is due to their ability to acquire new properties in the nanocrystalline state. Amorphous alloys are heterogeneous systems with amorphous matrices and frozen-in crystallization centers that exist in the metastable state; their properties thus substantially depend on the influence of external conditions (e.g., temperature, pressure, isothermal exposure time), especially in the field of phase transitions. Our statement of the problem results from the theory of amorphous alloy thermodynamic stability, according to which external effects (isothermal annealing or long exposure at room temperature) can substantially shift the phase equilibrium in a heterogeneous system with an amorphous matrix and frozen-in crystallization centers. The intervals of thermal stability and microhardness for a number of multicomponent amorphous cobalt-based alloys are determined. Based on the analysis of the theory of high-temperature thermodynamic stability of amorphous alloys, this study proposes a method for obtaining an amorphous-nanocrystalline state from the initial amorphous state by isothermal annealing at the temperatures where the controlled growth of frozen-in crystallization centres takes place. It is established that the part of the crystalline phase in the obtained materials became equal $X = (0.17 \div 0.31)${\%}, while their microhardness increased by ($14.6 \div 23.7$){\%} compared to the initial amorphous state, which is explained by the growth of frozen-in crystallization centers and the formation of amorphous-nanocrystalline state.

PACS number(s): 74.70.Ad, 64.75.+g

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