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Research Papers

Al2O3 Graded Coatings on Aluminum Alloy Deposited by the Fluidized Bed (FB) Technique: Film Formation and Mechanical Performance

[+] Author and Article Information
M. Barletta

Dipartimento di Ingegneria Meccanica, Università di Roma—“Tor Vergata”, Via del Politecnico, 1-00133, Rome, Italy

J. Eng. Mater. Technol 132(3), 031003 (Jun 15, 2010) (16 pages) doi:10.1115/1.4001263 History: Received June 02, 2009; Revised January 28, 2010; Published June 15, 2010; Online June 15, 2010

Al2O3 coatings have been deposited onto an Al alloy by the fluidized bed (FB) technique using alumina powder. Film formation through a cold deposition process and its growth kinetics have been investigated by varying the deposition time. This allowed us to establish how the morphology, microstructure, hardness, scratch resistance, and adhesion strength of the Al2O3 films were progressively imprinted. The FB process led to the deposition of a good-looking and well-adhered graded Al2O3 coating, which was found to be progressively richer in Al2O3 on moving from the interface with the Al alloy toward the outermost layers. The resulting Al2O3 coatings have been shown to produce a consistent improvement of the overall mechanical and tribological performance of the Al alloy, thus leading to the build-up of an overlying hard and tough protective layer.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Fluidized bed system: experimental set-up

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Figure 2

Map of the scratch strategy

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Figure 3

The growth of the Al2O3 thin film: mass accumulation versus FB processing time

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Figure 4

Morphology of the Al2O3 thin film after 15 min of FB processing: the surface is not completely coated

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Figure 5

Morphology of the Al2O3 thin film on sample 1 (30 min): complete surface coverage

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Figure 6

Morphology of the Al2O3 thin film on sample 4 (240 min): (a) overall view and (b) detail of Al2O3 debris

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Figure 7

Morphology of sample 2 (60 min) after cleaning under sonification: (a) large defects and (b) small cracks

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Figure 8

Roughness parameters of untreated and FB-treated samples

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Figure 9

θ/2θ and grazing incidence (ω=1 deg) XRD

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Figure 10

Cross-sections of sample 4 (240 min): (a) SE detector and (b) BSE detector

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Figure 11

EDXS microanalysis of cross-section: location of EDXS linear spots and EDXS smart map

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Figure 12

Quantitative EDXS analysis of linear spots in Fig. 9

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Figure 13

GDOES compositional depth profiling of Al2O3 film after 4 h FB deposition

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Figure 14

Depth-sensing indentation at different indentation depth performed on Al2O3 coatings deposited by FB with different deposition time

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Figure 15

Microvickers hardness test: FEG-SEM indentation images of 0.5 kg load test performed on an aluminum substrate FB-treated for 4 h at different magnifications—(a) SE detector and (b) BSE detector

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Figure 16

Microvickers hardness test: FEG-SEM indentation images of 1 kg load test performed on an aluminum substrate FB-treated for 4 h at different magnifications—(a) lower magnification and (b) higher magnification.

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Figure 17

Progressive load scratch test: friction force trends according to scratch pattern with FB processing time

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Figure 18

FEG-SEM images of progressive scratch patterns according to FB processing time using the BSE detector: (a) 30 min, (b) 60 min, (c) 120 min, and (d) 240 min

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Figure 19

FEG-SEM of the last part of a scratch pattern after scratch test performed on an aluminum substrate FB-treated for 4 h: (a) SE detector and (b) BSE detector

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Figure 20

3D maps of progressive scratch patterns according to FB processing time: (a) 30 min overall, (b) 60 min overall, (c) 120 min overall, and (d) 240 min overall

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Figure 21

Signals after progressive load scratch tests

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Figure 22

Residual scratch pattern after progressive load scratch test with 200 μm and 800 μm tip radius: (a) 200 μm tip radius overall view, (b) 800 μm tip radius overall view, (c) 200 μm tip radius high load, (d) 800 μm tip radius high load, (e) 200 μm tip radius, magnification of the scratch bottom at high load, and (f) 800 μm tip radius, magnification of the scratch bottom at high load

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Figure 23

Residual depth after continuous load scratch tests performed at different scratch speed

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Figure 24

Overall view of progressive and continuous load residual scratch patterns using an indenter with a 100 μm tip radius

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Figure 25

Residual scratch pattern after continuous load scratch test using an indenter with a 100 μm tip radius: (a) overall view, (b) high load, (c) coating material displaced sideways, and (d) coating material displaced in front of the advancing scratch geometry

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Figure 26

Wear pattern after pin-on-disk and linear reciprocating tests at 2.5 N and different sliding distance: (a) Al2O3 coated (after 4 h FB deposition) aluminum substrate and (b) uncoated aluminum substrate

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Figure 27

Wear pattern after pin-on-disk at 2.5 N and 500 m sliding distance on Al2O3 coated (after 4 h FB deposition) aluminum substrate at different magnifications

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Figure 28

Wear pattern after pin-on-disk at 5 N and 500 m sliding distance on Al2O3 coated (after 4 h FB deposition) aluminum substrate at different magnifications

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