Microstructural evolution of Nimonic 80a during hot forging under non-isothermal conditions of screw press

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Abstract

The microstructural evolution of nickel base superalloy Nimonic 80a during hot forging was studied in order to explore the suitability of this alloy to be hot forged under non-isothermal conditions of screw press, considering aspects such as deformation inhomogeneity, flow localization and shear bands formation. Hot forging trials in screw press with double truncated cones were carried out at three different temperatures, 950, 1050 & 1150 °C. The microstructure in the as-preheated condition was analysed in order to understand the impact of soaking temperature on the evolution of both grain size and precipitates/carbides prior to hot forging operations. In the as-forged condition, the impact of forging temperature, strain, strain rate and chilling effect of the dies on the microstructural evolution of Nimonic 80a was studied. No evidences of shear bands or flow localisation associated to adiabatic heating were found in the hot forged double truncated cones, indicating the suitability of Nimonic 80a to be processed in screw press. However, the non-isothermal conditions of screw press resulted into the development of heterogeneous structures across the thickness. Highly or fully unrecrystallized structures were observed in those areas in contact with bottom die, in contrast with top positions, where highly recrystallized structures were found. Soaking treatments play a very important role on microstructural evolution during hot forging for Nimonic 80a due to its strong impact on both grain growth and dissolution/precipitation of precipitates/carbides. For the present work, discontinuous dynamic recrystallization (DDRX) was found to be the main recrystallization mechanism for Nimonic 80a. Clear evidences of nucleation of new DRX grains by the formation of bulges in serrated grain boundaries with the subsequent growth by twinning were observed at the three forging temperatures. Particle-stimulated nucleation mechanism (PSN) is also operating in Nimonic 80a enhancing the heterogeneous nucleation of new grains in the interior of deformed grains
LanguageEnglish
Pages45-57
Number of pages13
JournalJournal of Materials Processing Technology
Volume252
Early online date9 Sep 2017
DOIs
Publication statusPublished - 28 Feb 2018

Fingerprint

Forging
Microstructural evolution
Nucleation
Truncated cone or frustum
Shear Bands
Shear bands
Carbides
Cones
Precipitates
Die
Dynamic Recrystallization
Chilling
Twinning
Grain Growth
Recrystallization
Superalloy
Temperature
Dynamic recrystallization
Dissolution
Grain Boundary

Keywords

  • hot forging
  • nickel base superalloys
  • Nimonic 80a
  • discontinuous dynamic recrystallization (DDRX)
  • non-isothermal conditions

Cite this

@article{9795766c1b084216b6df02825866f0eb,
title = "Microstructural evolution of Nimonic 80a during hot forging under non-isothermal conditions of screw press",
abstract = "The microstructural evolution of nickel base superalloy Nimonic 80a during hot forging was studied in order to explore the suitability of this alloy to be hot forged under non-isothermal conditions of screw press, considering aspects such as deformation inhomogeneity, flow localization and shear bands formation. Hot forging trials in screw press with double truncated cones were carried out at three different temperatures, 950, 1050 & 1150 °C. The microstructure in the as-preheated condition was analysed in order to understand the impact of soaking temperature on the evolution of both grain size and precipitates/carbides prior to hot forging operations. In the as-forged condition, the impact of forging temperature, strain, strain rate and chilling effect of the dies on the microstructural evolution of Nimonic 80a was studied. No evidences of shear bands or flow localisation associated to adiabatic heating were found in the hot forged double truncated cones, indicating the suitability of Nimonic 80a to be processed in screw press. However, the non-isothermal conditions of screw press resulted into the development of heterogeneous structures across the thickness. Highly or fully unrecrystallized structures were observed in those areas in contact with bottom die, in contrast with top positions, where highly recrystallized structures were found. Soaking treatments play a very important role on microstructural evolution during hot forging for Nimonic 80a due to its strong impact on both grain growth and dissolution/precipitation of precipitates/carbides. For the present work, discontinuous dynamic recrystallization (DDRX) was found to be the main recrystallization mechanism for Nimonic 80a. Clear evidences of nucleation of new DRX grains by the formation of bulges in serrated grain boundaries with the subsequent growth by twinning were observed at the three forging temperatures. Particle-stimulated nucleation mechanism (PSN) is also operating in Nimonic 80a enhancing the heterogeneous nucleation of new grains in the interior of deformed grains",
keywords = "hot forging, nickel base superalloys, Nimonic 80a, discontinuous dynamic recrystallization (DDRX), non-isothermal conditions",
author = "Marcos P{\'e}rez",
year = "2018",
month = "2",
day = "28",
doi = "10.1016/j.jmatprotec.2017.09.014",
language = "English",
volume = "252",
pages = "45--57",
journal = "Journal of Materials Processing Technology",
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TY - JOUR

T1 - Microstructural evolution of Nimonic 80a during hot forging under non-isothermal conditions of screw press

AU - Pérez, Marcos

PY - 2018/2/28

Y1 - 2018/2/28

N2 - The microstructural evolution of nickel base superalloy Nimonic 80a during hot forging was studied in order to explore the suitability of this alloy to be hot forged under non-isothermal conditions of screw press, considering aspects such as deformation inhomogeneity, flow localization and shear bands formation. Hot forging trials in screw press with double truncated cones were carried out at three different temperatures, 950, 1050 & 1150 °C. The microstructure in the as-preheated condition was analysed in order to understand the impact of soaking temperature on the evolution of both grain size and precipitates/carbides prior to hot forging operations. In the as-forged condition, the impact of forging temperature, strain, strain rate and chilling effect of the dies on the microstructural evolution of Nimonic 80a was studied. No evidences of shear bands or flow localisation associated to adiabatic heating were found in the hot forged double truncated cones, indicating the suitability of Nimonic 80a to be processed in screw press. However, the non-isothermal conditions of screw press resulted into the development of heterogeneous structures across the thickness. Highly or fully unrecrystallized structures were observed in those areas in contact with bottom die, in contrast with top positions, where highly recrystallized structures were found. Soaking treatments play a very important role on microstructural evolution during hot forging for Nimonic 80a due to its strong impact on both grain growth and dissolution/precipitation of precipitates/carbides. For the present work, discontinuous dynamic recrystallization (DDRX) was found to be the main recrystallization mechanism for Nimonic 80a. Clear evidences of nucleation of new DRX grains by the formation of bulges in serrated grain boundaries with the subsequent growth by twinning were observed at the three forging temperatures. Particle-stimulated nucleation mechanism (PSN) is also operating in Nimonic 80a enhancing the heterogeneous nucleation of new grains in the interior of deformed grains

AB - The microstructural evolution of nickel base superalloy Nimonic 80a during hot forging was studied in order to explore the suitability of this alloy to be hot forged under non-isothermal conditions of screw press, considering aspects such as deformation inhomogeneity, flow localization and shear bands formation. Hot forging trials in screw press with double truncated cones were carried out at three different temperatures, 950, 1050 & 1150 °C. The microstructure in the as-preheated condition was analysed in order to understand the impact of soaking temperature on the evolution of both grain size and precipitates/carbides prior to hot forging operations. In the as-forged condition, the impact of forging temperature, strain, strain rate and chilling effect of the dies on the microstructural evolution of Nimonic 80a was studied. No evidences of shear bands or flow localisation associated to adiabatic heating were found in the hot forged double truncated cones, indicating the suitability of Nimonic 80a to be processed in screw press. However, the non-isothermal conditions of screw press resulted into the development of heterogeneous structures across the thickness. Highly or fully unrecrystallized structures were observed in those areas in contact with bottom die, in contrast with top positions, where highly recrystallized structures were found. Soaking treatments play a very important role on microstructural evolution during hot forging for Nimonic 80a due to its strong impact on both grain growth and dissolution/precipitation of precipitates/carbides. For the present work, discontinuous dynamic recrystallization (DDRX) was found to be the main recrystallization mechanism for Nimonic 80a. Clear evidences of nucleation of new DRX grains by the formation of bulges in serrated grain boundaries with the subsequent growth by twinning were observed at the three forging temperatures. Particle-stimulated nucleation mechanism (PSN) is also operating in Nimonic 80a enhancing the heterogeneous nucleation of new grains in the interior of deformed grains

KW - hot forging

KW - nickel base superalloys

KW - Nimonic 80a

KW - discontinuous dynamic recrystallization (DDRX)

KW - non-isothermal conditions

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U2 - 10.1016/j.jmatprotec.2017.09.014

DO - 10.1016/j.jmatprotec.2017.09.014

M3 - Article

VL - 252

SP - 45

EP - 57

JO - Journal of Materials Processing Technology

T2 - Journal of Materials Processing Technology

JF - Journal of Materials Processing Technology

SN - 0924-0136

ER -