Solidification and microstructure formation of nickel based superalloy 718PLUS

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2025-1-09
Karadede, Berkhan
Alloy 718PlusTM is a Ni-based superalloy developed by ATI Allvac to increase Alloy 718 maximum service temperature by 55°C. Alloy 718 is widely used in aero gas turbine engines for its excellent performance at temperatures up to 649 °C. Alloy 718 stands out due to its favorable qualities, such as good forgeability, castability, and weldability. With advancements in gas turbine engine technology increasing the overall temperature capacity, the demand for cast static parts operable at higher temperatures is also evolving. Alloys like Rene 41 and Waspaloy can withstand higher temperatures than 649 °C; however, they present challenges in shaping, welding, and manufacturing. The Alloy 718 to 718PlusTM modification has made it a great alternative for applications requiring performance between 649°C and 760°C. 718Plus has already been used in forged form for gas turbine engines in the industry. This thesis explores the potential application of this alloy in cast form for static components. The effects of two different mould types—sand and metal—on the microstructure are compared. Alloy 718PlusTM was produced through induction melting under a protective argon atmosphere. Both revert 718 alloy and elemental raw materials were used in alloying 718PlusTM. Metal moulds produced finer dendritic structures. Homogenization of both castings showed different results. In sand casting, Laves phase dissolution is successfully achieved. However, in castings from metal moulds, Laves phases were not fully dissolved even after homogenization, showing brittle behavior. After solution treatment and aging, laves phase along the grain boundary were increased.
Citation Formats
B. Karadede, “Solidification and microstructure formation of nickel based superalloy 718PLUS,” M.S. - Master of Science, Middle East Technical University, 2025.