Effect of Ge and In on the structure and thermodynamic characteristics of high-entropy MnCoNiCu alloys

The study explores the feasibility of developing multi-component high-entropy filler metals for brazing various alloys. By employing computational methods alongside modified Hume-Rothery criteria, a promising MnCoNiCu-(In, Ge) system was identified. Various thermodynamic parameters were computed, establishing the structural dependencies of experimental alloys on alloying component content. Alloying limits adhering to criteria for high-entropy alloys were determined. Calculations revealed that MnCoNiCuIn₅ and MnCoNiCuGe₅ alloys crystallize, forming mixed solid solutions. Experimental investigations determined the solidus and liquidus temperatures of the promising alloys. MnCoNiCuIn₅ showed a range of 974–1089 °C, while MnCoNiCuGe₅ exhibited a melting range of 953.3–1100.6 °C. X-ray structural analysis confirmed a two-phase dendritic structure for experimental alloys, with primary phases being Mn–Co–Ni–Cu solid solution dendrites doped with indium or germanium, respectively. The secondary phase of the MnCoNiCuIn₅ alloy displayed increased concentrations of copper (up to 32 at.%) and indium (up to 15.14 at.%), while that of the MnCoNiCuGe₅ alloy showcased increased concentrations of manganese and germanium (35.79 at.% and 15.50 at.%, respectively). Results from both calculated and experimental studies support the potential utilization of the selected high-entropy alloys MnCoNiCuIn₅ and MnCoNiCuGe₅ as brazing filler metals.