Portevin-Le Chatelier Effect in Additively Manufactured and As-Cast Inconel 939 Nickel-Based Superalloy

Abstract

Nickel-based superalloys, well-established in aeronautics, have recently gained significant traction in additive manufacturing. Inconel 939 is one of the alloys increasingly playing a vital role in this field. This paper examines the development of the Portevin-Le Chatelier (PLC) effect in additively manufactured Inconel 939 in comparison with cast Inconel 939. A detailed analysis of tensile test characteristics was conducted, complemented by a high-resolution scanning electron microscopy (HR-SEM) investigation. The PLC region exhibited several properties during tensile testing, such as stress-strain behavior, cycle scale, and overall stress increase. The HR-SEM analysis of Gamma prime ( γ ') precipitates revealed distinct morphologies, which are suggested to be linked to the features of the PLC region. Samples with a high amount of γ ' precipitates showed a less pronounced PLC region, while those with fewer γ ' precipitates displayed a more distinct PLC effect. A mechanism for the cyclic drop-and-rise stress behavior, based on the work of Varvenne and La-Rose, was proposed, possibly induced by the varying morphologies of γ ' precipitates in the IN939 alloy. Further study is needed to deepen the understanding of the relationship between the γ ' micro-(nano) structure and the PLC phenomenon.