Microstructure and strengthening of Al-6Ce-3Ni-0.7Fe (wt%) alloy manufactured by laser powder-bed fusion

Tiffany Wu; Jonathan D. Poplawsky; Lawrence F. Allard; Alex Plotkowski; Amit Shyam; David C. Dunand

doi:10.1016/j.addma.2023.103858

Microstructure and strengthening of Al-6Ce-3Ni-0.7Fe (wt%) alloy manufactured by laser powder-bed fusion

Tiffany Wu, Jonathan D. Poplawsky, Lawrence F. Allard, Alex Plotkowski, Amit Shyam, David C. Dunand^*

^*Corresponding author for this work

Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

4 Scopus citations

Abstract

An Al-6Ce-3Ni-0.7Fe (wt%) alloy was fabricated via laser powder-bed fusion and its microstructure, thermal stability, tensile properties, and creep properties are investigated for two rapid-solidification rates with different eutectic spacings. For both faster- and slower-cooled states, the as-fabricated alloy mostly shows elongated grains with very fine eutectic networks (∼40 nm lamellar width) comprising a high-volume fraction (∼18 %) of intermetallic phases. Faster-cooled samples, however, display a less continuous eutectic network with finer spacing (∼100 nm), leading to higher Orowan strengthening and therefore superior microhardness and yield stress up to ∼350 °C. Upon aging (300 – 450 °C), micron-size Al₉(Ni,Fe)₂ needle-like precipitates form within grains, and the Al₁₁Ce₃ eutectic network spheroidizes, while retaining a submicron width and spacing, resulting in 33–37 % drop in microhardness after 144 h aging at 400 °C. Limited tensile ductility (∼6 %) and creep ductility (∼1–2 %) are measured for both faster- and slower-cooled alloys due to an inhomogeneous microstructure, where cavitation preferentially initiates at melt-pool boundaries, precipitate-free zones, and/or denuded zones, eventually leading to local fracture. Denuded zones, induced by stress, form due to diffusional flow with stress-dependent orientations, and are identified as microstructurally weak regions leading to strain localization. The present alloy does not show a significant difference in 300 °C creep resistance between: (i) tensile and compressive loading, (ii) faster- and slower-cooled samples, and (iii) continuous and spheroidized eutectics. Creep resistance at 300 °C is comparable to that of a Ce-richer Al-10.5Ce-3.1Ni-1.2Mn (wt%) alloy, despite the formation of denuded zones and needle-like Al₉(Ni,Fe)₂ precipitates.

Original language	English (US)
Article number	103858
Journal	Additive Manufacturing
Volume	78
DOIs	https://doi.org/10.1016/j.addma.2023.103858
State	Published - Sep 25 2023

Funding

TW was supported by the GO! Program from Oak Ridge National Laboratory (ORNL). This research was co-sponsored by the U.S. Department of Energy , Office of Energy Efficiency and Renewable Energy , Advanced Materials & Manufacturing Technology Office , and Vehicle Technologies Office Powertrain Materials Core Program (AP and AS). APT research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments. The authors would like to thank Kelsey Hedrick and Shane Hawkins for performing the tensile and tensile creep tests, Dana McClurg for performing the heat treatments, and Travis Dixon for electropolishing TEM samples.

Keywords

Additive manufacturing
Al alloys
Alloy design
Creep

ASJC Scopus subject areas

Biomedical Engineering
General Materials Science
Engineering (miscellaneous)
Industrial and Manufacturing Engineering

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10.1016/j.addma.2023.103858

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@article{35a1084d535947218073114ef41064e2,

title = "Microstructure and strengthening of Al-6Ce-3Ni-0.7Fe (wt%) alloy manufactured by laser powder-bed fusion",

abstract = "An Al-6Ce-3Ni-0.7Fe (wt%) alloy was fabricated via laser powder-bed fusion and its microstructure, thermal stability, tensile properties, and creep properties are investigated for two rapid-solidification rates with different eutectic spacings. For both faster- and slower-cooled states, the as-fabricated alloy mostly shows elongated grains with very fine eutectic networks (∼40 nm lamellar width) comprising a high-volume fraction (∼18 %) of intermetallic phases. Faster-cooled samples, however, display a less continuous eutectic network with finer spacing (∼100 nm), leading to higher Orowan strengthening and therefore superior microhardness and yield stress up to ∼350 °C. Upon aging (300 – 450 °C), micron-size Al9(Ni,Fe)2 needle-like precipitates form within grains, and the Al11Ce3 eutectic network spheroidizes, while retaining a submicron width and spacing, resulting in 33–37 % drop in microhardness after 144 h aging at 400 °C. Limited tensile ductility (∼6 %) and creep ductility (∼1–2 %) are measured for both faster- and slower-cooled alloys due to an inhomogeneous microstructure, where cavitation preferentially initiates at melt-pool boundaries, precipitate-free zones, and/or denuded zones, eventually leading to local fracture. Denuded zones, induced by stress, form due to diffusional flow with stress-dependent orientations, and are identified as microstructurally weak regions leading to strain localization. The present alloy does not show a significant difference in 300 °C creep resistance between: (i) tensile and compressive loading, (ii) faster- and slower-cooled samples, and (iii) continuous and spheroidized eutectics. Creep resistance at 300 °C is comparable to that of a Ce-richer Al-10.5Ce-3.1Ni-1.2Mn (wt%) alloy, despite the formation of denuded zones and needle-like Al9(Ni,Fe)2 precipitates.",

keywords = "Additive manufacturing, Al alloys, Alloy design, Creep",

author = "Tiffany Wu and Poplawsky, {Jonathan D.} and Allard, {Lawrence F.} and Alex Plotkowski and Amit Shyam and Dunand, {David C.}",

note = "Publisher Copyright: {\textcopyright} 2023 Elsevier B.V.",

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T1 - Microstructure and strengthening of Al-6Ce-3Ni-0.7Fe (wt%) alloy manufactured by laser powder-bed fusion

AU - Wu, Tiffany

AU - Poplawsky, Jonathan D.

AU - Allard, Lawrence F.

AU - Plotkowski, Alex

AU - Shyam, Amit

AU - Dunand, David C.

PY - 2023/9/25

Y1 - 2023/9/25

N2 - An Al-6Ce-3Ni-0.7Fe (wt%) alloy was fabricated via laser powder-bed fusion and its microstructure, thermal stability, tensile properties, and creep properties are investigated for two rapid-solidification rates with different eutectic spacings. For both faster- and slower-cooled states, the as-fabricated alloy mostly shows elongated grains with very fine eutectic networks (∼40 nm lamellar width) comprising a high-volume fraction (∼18 %) of intermetallic phases. Faster-cooled samples, however, display a less continuous eutectic network with finer spacing (∼100 nm), leading to higher Orowan strengthening and therefore superior microhardness and yield stress up to ∼350 °C. Upon aging (300 – 450 °C), micron-size Al9(Ni,Fe)2 needle-like precipitates form within grains, and the Al11Ce3 eutectic network spheroidizes, while retaining a submicron width and spacing, resulting in 33–37 % drop in microhardness after 144 h aging at 400 °C. Limited tensile ductility (∼6 %) and creep ductility (∼1–2 %) are measured for both faster- and slower-cooled alloys due to an inhomogeneous microstructure, where cavitation preferentially initiates at melt-pool boundaries, precipitate-free zones, and/or denuded zones, eventually leading to local fracture. Denuded zones, induced by stress, form due to diffusional flow with stress-dependent orientations, and are identified as microstructurally weak regions leading to strain localization. The present alloy does not show a significant difference in 300 °C creep resistance between: (i) tensile and compressive loading, (ii) faster- and slower-cooled samples, and (iii) continuous and spheroidized eutectics. Creep resistance at 300 °C is comparable to that of a Ce-richer Al-10.5Ce-3.1Ni-1.2Mn (wt%) alloy, despite the formation of denuded zones and needle-like Al9(Ni,Fe)2 precipitates.

AB - An Al-6Ce-3Ni-0.7Fe (wt%) alloy was fabricated via laser powder-bed fusion and its microstructure, thermal stability, tensile properties, and creep properties are investigated for two rapid-solidification rates with different eutectic spacings. For both faster- and slower-cooled states, the as-fabricated alloy mostly shows elongated grains with very fine eutectic networks (∼40 nm lamellar width) comprising a high-volume fraction (∼18 %) of intermetallic phases. Faster-cooled samples, however, display a less continuous eutectic network with finer spacing (∼100 nm), leading to higher Orowan strengthening and therefore superior microhardness and yield stress up to ∼350 °C. Upon aging (300 – 450 °C), micron-size Al9(Ni,Fe)2 needle-like precipitates form within grains, and the Al11Ce3 eutectic network spheroidizes, while retaining a submicron width and spacing, resulting in 33–37 % drop in microhardness after 144 h aging at 400 °C. Limited tensile ductility (∼6 %) and creep ductility (∼1–2 %) are measured for both faster- and slower-cooled alloys due to an inhomogeneous microstructure, where cavitation preferentially initiates at melt-pool boundaries, precipitate-free zones, and/or denuded zones, eventually leading to local fracture. Denuded zones, induced by stress, form due to diffusional flow with stress-dependent orientations, and are identified as microstructurally weak regions leading to strain localization. The present alloy does not show a significant difference in 300 °C creep resistance between: (i) tensile and compressive loading, (ii) faster- and slower-cooled samples, and (iii) continuous and spheroidized eutectics. Creep resistance at 300 °C is comparable to that of a Ce-richer Al-10.5Ce-3.1Ni-1.2Mn (wt%) alloy, despite the formation of denuded zones and needle-like Al9(Ni,Fe)2 precipitates.

KW - Additive manufacturing

KW - Al alloys

KW - Alloy design

KW - Creep

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Microstructure and strengthening of Al-6Ce-3Ni-0.7Fe (wt%) alloy manufactured by laser powder-bed fusion

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