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Research Papers: Coatings and Solid Lubricants

Effect of Flow Velocity and Impact Angle on Erosion–Corrosion Behavior of Chromium Carbide Coating

[+] Author and Article Information
A. R. Hemmati

Centre of Excellence for High Strength
Alloys Technology,
School of Metallurgy and Materials Engineering,
Iran University of Science and Technology,
Narmak,
Tehran 16844, Iran
e-mail: Alireza_Hemmati.1990@yahoo.com

M. Soltanieh

Centre of Excellence for High Strength
Alloys Technology,
School of Metallurgy and Materials Engineering,
Iran University of Science and Technology,
Narmak,
Tehran 16844, Iran
e-mail: Mansour_Soltanieh@iust.ac.ir

S. M. Masoudpanah

Centre of Excellence for High Strength
Alloys Technology,
School of Metallurgy and Materials Engineering,
Iran University of Science and Technology,
Narmak,
Tehran 16844, Iran
e-mail: Masoodpanah@iust.ac.ir

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received April 9, 2016; final manuscript received August 7, 2016; published online November 30, 2016. Assoc. Editor: Dae-Eun Kim.

J. Tribol 139(3), 031303 (Nov 30, 2016) (5 pages) Paper No: TRIB-16-1120; doi: 10.1115/1.4034424 History: Received April 09, 2016; Revised August 07, 2016

In this study, the effect of flow velocity (4–7.5 m s−1) and impact angle (30–90 deg) on erosion–corrosion behavior of chromium carbide coating was investigated under impingement by silica containing NaCl solution. Chromium carbide coating was deposited on low carbon steel by thermal reactive deposition/diffusion method at 1050 °C for 12 h in a molten salt bath. Mass loss measurement and potentiodynamic polarization tests were employed in order to determine coating performance under impingement. Polarization curves showed that the coated samples had less corrosion current density and high chemical stability. High mass loss at low impact angle indicated ductile behavior for the uncoated sample, while the mass loss for the coated sample changes less than 30% with impact angle up to 60 deg. Furthermore, the erosion–corrosion behavior of the coated sample was slightly dependent on flow velocity. Scanning electron micrographs showed that at lower impact angle, the Cr7C3 coating eroded with flake fragmentation mechanism, while at high impact angle, fatigue fracture is the main degradation mechanism.

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Figures

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Fig. 1

Schematic of erosion–corrosion test rig: (1) pump, (2) frequency inverter, (3) flow-controlled valve, (4) slurry container, (5) counter electrode, (6) nozzle, (7) reference electrode, (8) holder, (9) sample, (10) potentiostat, and (11) PC

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Fig. 2

(a) Cross section of Cr7C3 coating and (b) microhardness profile of chromized sample after TRD treatment at 1050 °C for 12 h

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Fig. 3

XRD pattern of chromium carbide coating (Cr7C3) in molten salt bath containing 85 wt.% borax–15 wt. % low carbon ferrochromium at 1050 °C for 12 h

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Fig. 4

Mass loss of uncoated and coated samples of test at various flow velocities at impact angle of 90 deg

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Fig. 5

Potentiodynamic polarization curve of Cr7C3 coated and uncoated specimens under erosion–corrosion condition at 5 m s−1 and impact angle of α = 90 deg

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Fig. 6

Mass loss of uncoated and Cr7C3 coated samples at various impact angles at 5 m s−1 flow velocity

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Fig. 7

Potentiodynamic polarization curve of uncoated and coated specimens at impact velocity of 5 m s−1 and at α = 45 deg

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Fig. 8

SEM micrograph of Cr7C3 coating surface after impingement at normal impact and at impact velocity: (a) 6 m s−1 and (b) 7.5 m s−1

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Fig. 9

SEM micrograph of Cr7C3 coating surface after impingement at 5 m s−1 impact velocity and at impact angle of (a) 90 deg and (b) 60 deg

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