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MM: Fachverband Metall- und Materialphysik

MM 61: Liquid & Amorphous Metals I

MM 61.3: Vortrag

Donnerstag, 14. März 2013, 16:15–16:30, H26

Phase separation in ternary Co-Gd-Ti liquids — •Junhee Han¹, Norbert Mattern¹, Dirk Holland-Moritz², Jozef Bednarcik³, Ivan Kaban¹, Rafal Nowak⁴, Natalia Sobczak⁴, and Jürgen Eckert¹ — ¹IFW-Dresden, Dresden, Germany — ²Institut für Materialphysik im Weltraum, DLR, Köln, Germany — ³HASYLAB, DESY, Hamburg, Germany — ⁴Center for High Temperature Studies, Foundry Research Institute, Krakow, Poland

Phase equilibrium and solidification behavior of ternary Co-Gd-Ti (Co ≤ 35 at. %) alloys has been investigated by thermal analysis (DSC) and microstructural characterization of cast alloys (SEM/EDX). The phase equilibria with the liquid phase were studied in situ for two alloys Co₃₀Gd₃₅Ti₃₅ and Co₃₀Gd₅₀Ti₂₀ by combining electrostatic levitation of the melt with high-energy synchrotron X-ray diffraction at elevated temperature. For Co₃₀Gd₃₅Ti₃₅ we observe two diffuse diffraction maxima (T = 1600 - 1700 K) giving direct evidence of liquid-liquid phase separation. The maxima positions exhibit a temperature dependent shift due to the change in chemical compositions with temperature in accordance with the binodal line. For Co₃₀Gd₅₀Ti₂₀, no indication of phase separation is detected. Coarsened microstructures typically for phase separated liquids are observed in cast alloys Co₃₀Gd₃₅Ti₃₅, Co₂₅Gd_37.5Ti_37.5, Co₁₀Gd₄₅Ti₄₅ and Co₃₀Gd₂₀Ti₅₀. Our findings suggest that the stable miscibility gap of the binary Gd-Ti extends into the ternary Gd-Ti-Co system (up to Co < 35 at. %). Thermodynamic calculations of the ternary Co-Gd-Ti by the CALPHAD method are in a good agreement with experimental findings.