Nanocomposites and nanomaterials

Influence of the method and regimes of the quenching from the liquid state on the microstructure of the Mg65Cu25Y10 alloy

Lysenko A.B.1, Zagorulko I.V.1, Kalinina T.V., Kugai N.A.1
1Dniprovsk State Technical University, Dniprobudivska str., 2, Kamyanske-51918, Ukraine. 
E-mail: zagorylko@ukr.net

The computational analysis of the thermal regimes and the crystallization kinetics of the Mg65Cu25Y10 alloy is carried out by the method of the coordinated numerical solution of the heat and kinetic tasks. The explored alloy was obtained by quenching of thin layers of the melt on a massive substrate and also by casting of the melt into a metal ingot with walls of finite thickness. The ingot was at room temperature or preheated to a temperature close to the glass transition temperature Tg of the Mg65Cu25Y10 alloy.
It is shown that with the use of traditional methods of rapid quenching, the processes of structure formation are carried out either under conditions of continuous cooling down to Tg or under the influence of a thermal regime involving the final stage of self-heating of the solidifying alloy through the voiding of latent heat of crystallization. Under these regimes, a wide range of structural states is fixed: from the truly amorphous to the microcrystalline, including intermediate conditionally amorphous and amorphous-crystalline structures.
In the case of casting a melt into a hot mold [1], whose initial temperature is = Tg + (3 – 50) К, the main volume fraction of the melt crystallizes under isothermal conditions that provide near-maximum nucleation rates (І ≈ 1016 – 1017 m-3·s-1) and negligible crystal growth rates (u ≈ 10-9 – 10-12m·s-1). With this combination of kinetic parameters I and u, the completely crystallized structures with crystal sizes from 65 to 150 nm are formed. 
The results of the performed analysis show the effectiveness of the proposed method of isothermal quenching of melts to produce alloys with predicted nanocrystalline structures. They can find application in the field of production of massive nanomaterials.

1. Лисенко О.Б., Кравець О.Л., Косинська О.Л., Лисенко О.О., Губарєв С.В., Калініна Т.В. Спосіб виготовлення об’ємних нанокристалічних сплавів: патент № 64872, Україна . – № u 201104033, опубл. 25.11.2011, бюл. №22.