Nanoscale serration characteristics of additively manufactured superalloys

Structural elements made of nickel-based superalloys usually operate at high temperatures. Many surface failure mechanisms such as creep, fatigue, fretting fatigue, corrosion, and stress corrosion cracking start from the surface. Thus, studying the surface mechanical properties and deformation behavior of materials is vital in order to draw a correlation between the surface properties and failures. Herein, a nanoindentation technique was implemented to characterize surface properties of a widely used additively manufactured (AM) superalloy, i.e., Inconel 625. The specimens were tested in a range of temperatures in a vacuum chamber. Serrated plastic flow characterized by pop-in events during nanoindentation, known as Portevin-Le Chatelier (PLC) effect, was observed in all three tested elevated temperatures. This phenomenon depicts itself as bursts of plasticity in the loading section of the load-displacement curves. These bursts were studied comprehensively to explore incipient plasticity. Hertzian contact mechanics were implemented to extract the maximum shear stress beneath the indenter from the pop-in loads. The results show that the initial pop-in load increases as the temperature increases. The average initial pop-in load increases by almost four times from 300 degrees C to 650 degrees C. This was attributed to the formation of strengthening precipitates. The average size of the serrations and the magnitude of dislocation nucleation increase from 300 degrees C to 500 degrees C and decrease from 500 degrees C to 650 degrees C. The serrations are attributed to the dislocation generation and movement as well as their interaction with the solute YYatoms and precipitates. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Research on surface mechanical properties and deformation behavior of nickel-based superalloys, such as Inconel 625, using nanoindentation technique revealed that the initial pop-in load during serrated plastic flow increases with temperature due to the formation of strengthening precipitates. The size of serrations and dislocation nucleation also show a trend with changing temperature.