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7154 |
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High entropy alloy brazing filler metal design for joining Cu to CuCrZr at intermediate temperatures |
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Dan Luo / The Univerisity of Sheffield, Great Britain Russell Goodall / Univeristy of Sheffield, Great Britain Robert Snell/ The University of Sheffield, United Kingdom Martin Cuddy/ UK Atomic Energy Authority, United Kingdom James Redman/ The Welding Institute, United Kingdom Nick Ludford/ The Welding Institute, United Kingdom |
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High entropy alloy (HEA) brazing fillers have attracted more and more attention in the last few years. High configurational entropies in HEAs can stabilise solid-solution phases, avoiding the formation of detrimental intermetallics. The multiple principal alloying elements in HEA fillers could also potentially widen the joining temperatures, especially the intermediate temperatures around the brazing and soldering temperature watershed of 450?C, e.g. 325-550?C where the temperature region is poorly occupied by the standard fillers. In this study, we have used two steps to design HEA fillers for joining Cu to CuCrZr at intermediate temperatures to reduce the degradation of Cu base materials when joining at high temperatures in a fusion application. The initial HEA selection process was conducted using a rapid large-scale Python programming screening calculations technique based on HEA formation parameters (atomic size mismatch, enthalpy of mixing and entropy of mixing). Mixing melting temperature was also added in the Python calculations, resulting in a series of alloys. Thermo-Calc was then used to refine these alloys further. AuCuInAlGe and CuGeNiGaSb HEA fillers were finally obtained. The solidus is 432 ?C and 413?C for AuCuInAlGe and CuGeNiGaSb, respectively, and the liquidus is 566?C and 555?C from the Thermo-Calc calculations. The microstructure and mechanical properties of the joints were examined after these two HEA fillers were used to join the Cu to CrCrZr alloy. |