Investigation of oxide inclusion films in cast superalloy impeller

Oxide inclusions are commonly found in casting alloys. During vacuum investment casting of polycrystalline nickel-based superalloy, various forms of oxide inclusions can be observed, including membrane-like inclusions. These oxide inclusion films can significantly reduce the mechanical properties of nickel-based superalloys. A cast superalloy impeller that fractured due to internal oxide inclusion films was analyzed in this article. The objective of this article is to analyze the morphology and composition of oxide inclusion films and investigate their formation mechanisms. This article uses a scanning electron microscope and transmission electron microscope to characterize oxide inclusion film samples. The results show that the oxide inclusions are composed of film-like alumina, magnesium-aluminium spinel, and magnesia particles encapsulated by magnesium-aluminium spinel films. The oxide inclusion films are formed through a reaction between the liquid metal melt and the magnesia crucible. These oxide films are then floating into the nickel matrix through the scouring of the liquid metal melt and become internal inclusions.