Resource recycling of superalloys and hydrometallurgical challenges

Abstract

Superalloys are high melting temperature, excellent creep resistance, anti-corrosive, and oxidation resistant alloys; they are predominantly used in gas turbines of aircraft engines and power plants. Today, a series of superalloys is available according to their composition and applications. The tough nature of superalloys makes it difficult to recycle them after they are formed; this increases the demand and shortage of the energy-critical elements that are their raw materials and makes their processing one of the most demanding form of recycling today. A few processes are available, and some of these unique recycling systems are in use; however, a lack of data and/or information exists for two reasons: (i) scrap recycling is most frequently performed by superalloy manufacturers themselves (not always by the same unit) by recharging them into molten charges, and (ii) the recycler does not want to produce business for their rivals. This article presents an overview of the processes investigated to recycle superalloys, including the advantages and disadvantages of each. The available processes are not very technologically or economically feasible; therefore, further efforts are necessary to explore these processes and to make a value-added product by recycling superalloys rather than just re-melting them. Considering the continuously increasing number of alloyed elements in advanced superalloys, this paper also notes to the challenges associated with hydrometallurgical recycling of superalloys and the need for future studies on this topic.