Role of the Secondary Phase \u03b7 During High-Temperature Compression of ATI 718Plus\xae

Christiane Kienl,Himanshu Lalvani,Paranjayee Mandal,Catherine M F Rae

doi:10.1007/s11661-020-05837-7

Christiane Kienl, Himanshu Lalvani + Show 2 more

Open Access

https://doi.org/10.1007/s11661-020-05837-7

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Abstract

High-temperature compression tests were performed on a Ni-base superalloy with a multi-phase microstructure. Particular attention was given on the influence of the η phase on recrystallization of ATI 718Plus®. The compression tests were performed at two temperatures over a variety of strains and strain rates. Meta-dynamic recrystallization was studied by exposing the samples to a set dwell time at the test temperature after deformation. Electron backscatter diffraction (EBSD) was used to investigate the microstructures after the tests. Secondary electron imaging (SEI) and scanning transmission electron microscopy (STEM) were utilized in order to investigate the deformation behavior of η and obtaining a detailed understanding of the recrystallization mechanism. The secondary η phase was found to increase the recrystallized fraction compared to η free tests. However, clusters of thin lamellar η inhibited recrystallization. The flow curve softening was distinctly stronger in the microstructure containing precipitates. It could be shown by SE images that this was due to the breakage and realignment of η. In addition, η was also found to accommodate the stresses by a remarkable deformation without breaking up. This was considered to be due to the composite nature of the precipitate as well as the ongoing recrystallization in the surrounding matrix.

Highlights

DYNAMIC recrystallization (DRX) is a restorative mechanism of the microstructure which occurs during the forging of an alloy
With heating rate of 12 C minÀ1 the temperature was raised to the respective testing temperature, which was maintained within ± 2 deg
We suggest that the yield drop could be due to the rapid multiplication of twins in the early stages of deformation immediately following yield

Summary

Introduction

DYNAMIC recrystallization (DRX) is a restorative mechanism of the microstructure which occurs during the forging of an alloy. For critical components such as turbine disks in jet engines, a homogeneous microstructure after the forging is key to prevent failure. Ni-base superalloys are the material of choice for turbine disks in the high pressure section of an aero engine. One of which is ATI 718PlusÒ (hereafter 718Plus), a multi-phase strengthening polycrystalline Ni-base superalloy. The second precipitate found in 718Plus is the hexagonal g phase (Ni6[Al,Ti]Nb) which is interlayered with narrow orthorhombic d (Ni3Nb).[1,2] The g morphology depends on the thermo-mechanical history of Manuscript submitted February 2, 2020.

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