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Research Papers

Comparative Abrasive Wear Study of HVOF Coatings Obtained by Spraying WC-17Co Microcrystalline and Duplex Near-Nanocrystalline Cermet Powders

[+] Author and Article Information
G. C. Saha1

 Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canadagsaha@ucalgary.ca

T. I. Khan

 Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

1

Corresponding author.

J. Eng. Mater. Technol 133(4), 041002 (Oct 13, 2011) (8 pages) doi:10.1115/1.4004689 History: Received March 07, 2011; Revised July 12, 2011; Accepted July 22, 2011; Published October 13, 2011; Online October 13, 2011

High velocity oxy-fuel spraying was used to develop a near-nanocrystalline coating from a duplex Co coated WC-17Co powder feedstock. A microstructural and mechanical property characterization of the coating with a similar microcrystalline coating of the same composition was made. X-ray diffraction analysis showed less decarburization of the nanocrystalline coating and a more homogeneous coating structure than the microcrystalline coating produced under the same spraying conditions. The mechanical assessment of the coatings was performed using microhardness and indentation fracture toughness measurements. The abrasive wear resistance was determined using the ASTM G65-04 dry-sand rubber wheel test. The results showed that the hardness of the near-nanocrystalline coating was 25% greater than that of the microcrystalline coating and a sixfold increase in the abrasive wear resistance was also recorded for the near-nanocrystalline coating. Examination of the worn surfaces using atomic force microscopy after abrasive testing showed a smoother surface roughness in the near-nanocrystalline coating than that of the microcrystalline coating surface. The increase in fracture toughness of the near-nanocrystalline coating prevented brittle fracture of the coating surface.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

SEM micrographs comparing near-nanocrystalline WC-17Co powder particles (a) after mechanical alloying and spray drying; (b) after cobalt outer coating; with (c) microcrystalline WC-17Co powder particles

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Figure 2

SEM micrographs showing near-nanocrystalline WC-17Co powder particle (a) cross-section and (b) WC grain size estimates

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Figure 3

Schematic of the high velocity oxy-fuel (HVOF) thermal spraying of cermet powders

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Figure 4

SEM micrographs comparing microstructures of WC-17Co microcrystalline and near-nanocrystalline coatings: (a) and (d) coat thickness; (b) and (e) lamellar structure exhibiting reacted layers and carbide distribution; (c) and (f) magnification of (b) and (e), respectively

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Figure 5

SEM micrographs showing the presence of (a) partially melt and (b) agglomerated WC-17Co near-nanocrystalline particles in the HVOF coating

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Figure 6

XRD analysis of the microcrystalline and near-nanocrystalline WC-17Co coatings after spraying

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Figure 7

Graphs showing variation in microhardness as a function of coating depth through the microcrystalline and near-nanocrystalline WC-17Co coatings

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Figure 8

Fracture toughness as a function of hardness of WC-Co cermets with nanocrystalline and microcrystalline WC grains [14]

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Figure 9

A comparison between fracture toughness and hardness of microcrystalline and near-nanocrystalline WC-17Co coatings

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Figure 10

Abrasive wear rate as a function of time for microcrystalline and near-nanocrystalline WC-17Co coatings

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Figure 11

SEM micrographs showing dry-sand rubber wheel abrasive worn surfaces of (a) microcrystalline and (b) near-nanocrystalline WC-17Co coatings

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Figure 12

AFM three-dimensional views showing dry-sand rubber wheel abrasive worn surfaces of (a) microcrystalline and (b) near-nanocrystalline WC-17Co coatings

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Figure 13

Surface roughness versus probe distance of microcrystalline and near-nanocrystalline coatings after G65 abrasive wear

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