Nanocomposites and nanomaterials

The structure of the alloy Cu47Ni8Ti34Zr11 obtained under isothermal conditions of quenching from the liquid state
Kosynska O.L., Shevelieva K.Yu.
Dniprovsk State Technical University
Dniprostroevska str., 2a, Kamianske, 52818, Ukraine
E-mail: krao@ua.fm

The results of computational analysis of thermal conditions and the crystallization kinetics of castings from the bulk metallic glass Cu47Ni8Ti34Zr11 (Vit101), obtained by rapid quenching in a hot copper mold are presented. Studies of the castings structure formation process under the conditions of isothermal melt quenching were performed by the method of agreed numerical solution of the heat conduction equations and the mass crystallization kinetics. When creating the corresponding model, it was assumed that the melt having the initial temperature  is poured into a copper mold preheated to a temperature . After filling the working cavity of the mold, the melt begins to cool by transferring heat in two opposite directions perpendicular to the walls of the mold. 
To study the effect of the temperature of the mold on the thermal conditions and the crystallization kinetics of castings from Vit 101 alloy, calculated the time dependences of the temperatures of the melt T1(t) and the mold T2(t), as well as the fraction of the crystallized volume x(t). The calculations were performed for castings with a thickness of l1=0,510-3m, obtained by melt casting into a Cu-mold with a thickness of heat-removing walls l2=1510-3m. The preheat temperature of the mold  was varied from 323 to 764K. Analysis of the calculated data shows that when the mold is heated to temperatures not exceeding the alloy glass transition temperature Tg=671K, the isothermal mode of castings solidification is not realized. When the mold is heated to temperatures >Tg, the thermal conditions and the castings solidification kinetics change qualitatively. The interval of the mold initial temperature values  was determined, providing the establishment of the castings solidification isothermal mode at temperatures (5–93)K higher than the glass transition point. It was shown that at the isothermal stage of the process, crystallization takes place with close to maximum (1015–1018) m-3s-1 nucleation rates and very low (10-13–10-8) ms-1 crystal growth rates as a result, fully crystallized structures with average crystal sizes from 63 to 240 nm are fixed.