Production and characterization of low-density silicon nitride reinforced zinc nanocomposite coatings on mild steel for applications in marine and automotive industries

Abstract

In today's automotive, marine and petrochemical industries, the desire for lightweight materials has increased. Hence, necessitating the production of components with low density. In this work, lightweight Zn-Si₃N₄ coatings were developed by including Si₃N₄ in the zinc matrix. The optimal coatings were produced on steel samples at 45 °C and varied Si₃N₄ particles and voltages following ASTM A53/A53M standard. The deterioration (corrosion) property i.e. corrosion rate (CR) and current density (j_ocorr) of the uncoated (control) and coated samples were examined in 0.5 M of sulphuric acid using a potentiodynamic polarization technique following ASTM G3/G102 standard. The microstructure of the samples was studied via the SEM micrographs and XRD patterns, while the wear performance resistance (following ASTM G99 standard) and electrical conductivity of the samples were examined with a pin-on-disc tribometer and ammeter-voltmeter. The corrosion experiment indicated that the uncoated mild steel specimen possessed a CR of 12.345 mm year^-1 and j_ocorr of 1060 μA/cm², while the CR and j_corr of the coated samples ranged from 2.6793 to 4.7975 mm year^-1 and 231-413 μA/cm², respectively. The lower CR and j_corr values of the coated specimens, relative to the coated sample showed that the coatings possessed superior passivation ability in the test medium. The SEM micrographs of the samples showed refined morphology, while the XRD patterns revealed high peak intensity crystals such as Zn₄SiN, ZnNSi, Zn₄N and Zn₂NSi, which could be beneficial to the mechanical properties and corrosion resistance of the steel. Moreover, the wear resistance study indicated that the COF of the uncoated sample ranged from 0.1 to 0.5, while those for coated specimens ranged from 0.05 to 0.35. Similarly, the uncoated steel exhibited a wear volume (WV) of 0.00508 mm³, while the WV of the coated specimens ranged from 0.00266 to 0.0028 mm3, indicating the existence of high strengthening mechanisms between the interface of the protecting device and the steel. Also, the electrical conductivity of the mild steel sample reduced from 12.97 Ω^-1cm^-1 to 0.64 Ω^-1cm^-1, indicating that the electrical resistivity of the steel was enhanced by the coatings.

Keywords: Coatings; Corrosion rate; Mild steel; Wear volume; Zn-Si3N4; low density.

Fig. 1

Schematic of Electrodeposition process [18].

Fig. 2

(a) Coating thickness and (b) Weight gained by samples.

Fig. 3

Corrosion rate of samples.

Fig. 4

Corrosion current density of samples.

Fig. 5

Polarization resistance of samples.

Fig. 6

Tafel plots for samples.

Fig. 7

Efficiencies of Zn–Si₃N₄ coatings.

Fig. 8

Plot of OCP against time for samples.

Fig. 9

SEM and EDS of the uncoated steel.

Fig. 10

SEM and EDS of Si₃N₄ particles.

Fig. 11

SEM and EDS of 0.3Zn–7Si₃N₄ coating.

Fig. 12

SEM and EDS of 0.5Zn–7Si₃N₄ coating.

Fig. 13

SEM and EDS of 0.3Zn–13Si₃N₄ coating.

Fig. 14

SEM and EDS of 0.5Zn–13Si₃N₄ coating.

Fig. 15

XRD pattern for 0.3Zn–7Si₃N₄ coating.

Fig. 16

XRD pattern for 0.5Zn–7Si₃N₄ coating.

Fig. 17

XRD pattern for 0.3Zn–13Si₃N₄ coating.

Fig. 18

XRD pattern for 0.5Zn–13Si₃N₄ coating.

Fig. 19

Wear volume of the samples.

Fig. 20

COF of the samples.

Fig. 21

SEM image of wear scar on the control sample.

Fig. 22

SEM image of the wear scar on 0.3Zn–7Si₃N₄sample.

Fig. 23

SEM image of the wear scar on 0.5Zn–7Si₃N₄ coated sample.

Fig. 24

SEM image of the wear scar on 0.3Zn–13Si₃N₄ coated sample.

Fig. 25

SEM image of the wear scar on 0.5Zn–13Si₃N₄ coated sample.

Fig. 26

Electrical conductivity of the control sample and coated samples.