Anomalous precipitation hardening in Al-(1 wt%)Cu thin films

LI J.C. Bergers, J.Th.M. De Hosson, M.G.D. Geers, J.P.M. Hoefnagels

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Abstract

This paper concentrates on the precipitation hardening of Al-(1 wt%)Cu thin films. It is shown that in contrast to bulk, the well-known approach of precipitation hardening in confined systems like thin layers and thin films does not operate in the conventional way. This work analyses and discusses the precipitate hardening and its relation to the precipitation mechanism of Al-(1 wt%)Cu thin films which are subjected to precipitation hardening, nano-indentation hardness measurements. Microfabricated Al-(1 wt%)Cu thin films were solution treated at 550 °C for 15 min, quenched and aged at 190 °C for various durations up to 48 h. Nano-indentation hardness measurements revealed for the first time an unexpected decrease in hardness at just ∼8 hours of aging, followed by a saturating increase. Microstructural analysis employing electron microscopy (high-resolution transmission, scanning, backscatter diffraction, energy dispersive spectroscopy) and x-ray diffraction revealed GP zones and θ precipitates but no θ’ in as-received films, and only θ precipitates for aging durations longer than 6 h in the precipitate hardened films. Through-thickness analyses of aged specimens highlighted that θ precipitates nucleate and grow essentially at grain boundary grooves and at the specimen surface as preferential nucleation sites, while depleting Cu from the grain interior. It is shown that the growing precipitation at the surface and grain boundary grooves depletes the Cu in the thin film interior explaining the weakening-hardening sequence observed in the hardness measurements. Hence, the work shows that precipitation kinetics, and not thermodynamics, determine the precipitation state in thin films.

Original languageEnglish
Pages (from-to)37-46
Number of pages10
JournalMaterials Science and Engineering A
Volume722
DOIs
Publication statusPublished - 11 Apr 2018

Fingerprint

precipitation hardening
Age hardening
Precipitates
precipitates
Thin films
hardness
thin films
Hardness
Nanoindentation
nanoindentation
hardening
grooves
Hardening
Grain boundaries
grain boundaries
Aging of materials
Diffraction
High resolution transmission electron microscopy
Energy dispersive spectroscopy
electron microscopy

Keywords

  • Al-Cu alloy
  • EDS
  • Nanoindentation
  • Precipitation hardening
  • TEM
  • Thin film
  • XRD

Cite this

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title = "Anomalous precipitation hardening in Al-(1 wt{\%})Cu thin films",
abstract = "This paper concentrates on the precipitation hardening of Al-(1 wt{\%})Cu thin films. It is shown that in contrast to bulk, the well-known approach of precipitation hardening in confined systems like thin layers and thin films does not operate in the conventional way. This work analyses and discusses the precipitate hardening and its relation to the precipitation mechanism of Al-(1 wt{\%})Cu thin films which are subjected to precipitation hardening, nano-indentation hardness measurements. Microfabricated Al-(1 wt{\%})Cu thin films were solution treated at 550 °C for 15 min, quenched and aged at 190 °C for various durations up to 48 h. Nano-indentation hardness measurements revealed for the first time an unexpected decrease in hardness at just ∼8 hours of aging, followed by a saturating increase. Microstructural analysis employing electron microscopy (high-resolution transmission, scanning, backscatter diffraction, energy dispersive spectroscopy) and x-ray diffraction revealed GP zones and θ precipitates but no θ’ in as-received films, and only θ precipitates for aging durations longer than 6 h in the precipitate hardened films. Through-thickness analyses of aged specimens highlighted that θ precipitates nucleate and grow essentially at grain boundary grooves and at the specimen surface as preferential nucleation sites, while depleting Cu from the grain interior. It is shown that the growing precipitation at the surface and grain boundary grooves depletes the Cu in the thin film interior explaining the weakening-hardening sequence observed in the hardness measurements. Hence, the work shows that precipitation kinetics, and not thermodynamics, determine the precipitation state in thin films.",
keywords = "Al-Cu alloy, EDS, Nanoindentation, Precipitation hardening, TEM, Thin film, XRD",
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Anomalous precipitation hardening in Al-(1 wt%)Cu thin films. / Bergers, LI J.C.; De Hosson, J.Th.M.; Geers, M.G.D.; Hoefnagels, J.P.M.

In: Materials Science and Engineering A, Vol. 722, 11.04.2018, p. 37-46.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Anomalous precipitation hardening in Al-(1 wt%)Cu thin films

AU - Bergers, LI J.C.

AU - De Hosson, J.Th.M.

AU - Geers, M.G.D.

AU - Hoefnagels, J.P.M.

PY - 2018/4/11

Y1 - 2018/4/11

N2 - This paper concentrates on the precipitation hardening of Al-(1 wt%)Cu thin films. It is shown that in contrast to bulk, the well-known approach of precipitation hardening in confined systems like thin layers and thin films does not operate in the conventional way. This work analyses and discusses the precipitate hardening and its relation to the precipitation mechanism of Al-(1 wt%)Cu thin films which are subjected to precipitation hardening, nano-indentation hardness measurements. Microfabricated Al-(1 wt%)Cu thin films were solution treated at 550 °C for 15 min, quenched and aged at 190 °C for various durations up to 48 h. Nano-indentation hardness measurements revealed for the first time an unexpected decrease in hardness at just ∼8 hours of aging, followed by a saturating increase. Microstructural analysis employing electron microscopy (high-resolution transmission, scanning, backscatter diffraction, energy dispersive spectroscopy) and x-ray diffraction revealed GP zones and θ precipitates but no θ’ in as-received films, and only θ precipitates for aging durations longer than 6 h in the precipitate hardened films. Through-thickness analyses of aged specimens highlighted that θ precipitates nucleate and grow essentially at grain boundary grooves and at the specimen surface as preferential nucleation sites, while depleting Cu from the grain interior. It is shown that the growing precipitation at the surface and grain boundary grooves depletes the Cu in the thin film interior explaining the weakening-hardening sequence observed in the hardness measurements. Hence, the work shows that precipitation kinetics, and not thermodynamics, determine the precipitation state in thin films.

AB - This paper concentrates on the precipitation hardening of Al-(1 wt%)Cu thin films. It is shown that in contrast to bulk, the well-known approach of precipitation hardening in confined systems like thin layers and thin films does not operate in the conventional way. This work analyses and discusses the precipitate hardening and its relation to the precipitation mechanism of Al-(1 wt%)Cu thin films which are subjected to precipitation hardening, nano-indentation hardness measurements. Microfabricated Al-(1 wt%)Cu thin films were solution treated at 550 °C for 15 min, quenched and aged at 190 °C for various durations up to 48 h. Nano-indentation hardness measurements revealed for the first time an unexpected decrease in hardness at just ∼8 hours of aging, followed by a saturating increase. Microstructural analysis employing electron microscopy (high-resolution transmission, scanning, backscatter diffraction, energy dispersive spectroscopy) and x-ray diffraction revealed GP zones and θ precipitates but no θ’ in as-received films, and only θ precipitates for aging durations longer than 6 h in the precipitate hardened films. Through-thickness analyses of aged specimens highlighted that θ precipitates nucleate and grow essentially at grain boundary grooves and at the specimen surface as preferential nucleation sites, while depleting Cu from the grain interior. It is shown that the growing precipitation at the surface and grain boundary grooves depletes the Cu in the thin film interior explaining the weakening-hardening sequence observed in the hardness measurements. Hence, the work shows that precipitation kinetics, and not thermodynamics, determine the precipitation state in thin films.

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KW - EDS

KW - Nanoindentation

KW - Precipitation hardening

KW - TEM

KW - Thin film

KW - XRD

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M3 - Article

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EP - 46

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JF - Materials Science and Engineering A

SN - 0921-5093

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