Abstract
Ni–Mo alloy coatings were deposited by high velocity oxy-fuel spraying (HVOF) and air plasma spraying (APS). The merit and demerit of the two processes were compared according to the microstructure, mechanical properties, tribological performance and corrosion resistance to HCl. Results show that the microstructure of HVOF coating is uniform and dense with a porosity of 0.62%, a microhardness of 474.7HV0.3 and a bonding strength of 58.8 MPa. Compared with the HVOF coating, the APS coating exhibits a lamellar structure and numerous pores/microcracks with a higher porosity of 3.28%, a lower microhardness of 300.8HV0.3 and a worse bonding strength of 40.6 MPa. XRD and XPS analyses show that almost no phase transformation and oxidation happen during both spraying processes. The HVOF coating has a lower wear rate of 2.82 × 10−3mm3 N−1∙m−1 and a higher friction coefficient of about 0.75 than those of the APS coating. The wear mechanism of both coatings contains the adhesive wear, abrasive wear and oxidation wear. Combining the potentiodynamic polarization curves and EIS results, it shows that the HVOF coating has a better corrosion resistance to HCl than the APS coating. The relatively dense microstructure and excellent cohesive bonding between deposited particles take the main responsibility.
Published Version
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