Spinodally decomposed patterns in rapidly quenched Co-Cu melts

Abstract

The Co-Cu system is analyzed in the region of metastable miscibility gap with separation of the undercooled melt into Co-rich and Cu-rich liquids [1]. Phase separation of undercooled and quenched samples of Co50Cu50 melt are investigated experimentally using electromagnetic levitation (EML) technique, quenching the undercooled melt onto a Pb-solder coated copper chill substrate and by splat quenching methods. It is found that quenching of the liquid samples with cooling rates of 106-107 K/s leads to a frozen in microstructure of spinodally decomposed liquids. The composition of the Co-rich phase measured by TEM-EDS is Co71.7Cu28.3 and that of the Cu-rich phase is Co26.8Cu73.2. These compositions are inside the spinodal region and close to the calculated spinodal boundary in the phase diagram of the Co-Cu system. The spinodally separated samples have periodicity of mean distance between patterns of about 0.12-0.4 μm. Using the model of fast spinodal decomposition (see Ref. [2] and references therein), computational modelling is carried out using semi-implicit numeric scheme as described in Ref. [3]. The results of modelling confirm the ability to quantitatively reproduce experimentally frozen spinodal patterns by their periodicity. The calculated time for the complete phase separation into the Co-rich and Cu-rich phases (in evolution spinodally decomposing patterns) is greater than the time for samples solidifying at cooling rates of 106-107 K/s. References [1] M. Kolbe, C.D. Cao, X.Y. Lu, P.K. Galenko, B. Wei, D.M. Herlach, Materials Science and Engineering A 375-377, 520 (2004). [2] P. Galenko, D. Jou, Physica A 388, 3113 (2009). [3] N. Lecoq, H. Zapolsky, P. Galenko, The European Physical Journal ST 177 165 (2009).