Effect of Laser Remelting on Microstructure and Corrosion Resistance of Plasma Sprayed AlCoCrFeNi High-entropy Alloy Coating
The high cost of producing multi-principal component high-entropy alloys(HEAs)has limited their widespread application,despite their superior properties.Applying HEA coatings to conventional metals can harness these exceptional properties while conserving precious metal resources.Nonetheless,HEA coatings frequently exhibit defects like pores and cracks,which significantly impair their functionality.Research has demonstrated that laser remelting can effectively mitigate most of these defects,refining the coatings'microstructure and enhancing their overall performance.Although existing studies on laser-remelted HEA coatings have primarily concentrated on their microstructure,mechanical attributes,and wear resistance,the impact of laser remelting on their corrosion resistance remains less explored.This investigation assessed the corrosion resistance of an AlCoCrFeNi HEA coating applied to AISI 1045 steel via plasma spraying,followed by laser remelting.The coatings'microstructures,both pre-and post-remelting,were examined using scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS),with a particular focus on the elemental distribution at the coating-substrate interface.Phase analysis was conducted using X-ray diffraction(XRD),while transmission electron microscopy(TEM)provided insights into the microstructural details of both coatings.Electrochemical and immersion corrosion tests evaluated the coatings'resistance to corrosion.The findings revealed that laser remelting substantially reduced the defects present in the plasma-sprayed coating,decreasing porosity from 4.8％to a negligible 0.3％.This process also converted the mechanical bonding between the coating and substrate into a stronger metallurgical bond.Despite the remelting process,the elemental composition of the coating remained close to an equimolar ratio,consistent with HEA definitions.The laser-remelted coating exhibited a predominance of the BCC solid solution phase,alongside minor FCC phase precipitates,with a higher BCC content than the original sprayed coating.This resulted in a uniform and dense microstructure,characterized by dendritic and interdendritic patterns.Electrochemical tests,including polarization curve analysis and electrochemical impedance spectroscopy,indicated that laser remelting significantly enhances the corrosion resistance of the AlCoCrFeNi HEA coating in a 3.5％NaCl solution.Laser remelting significantly enhanced the corrosion resistance of the HEA coating,evidenced by an increase in self-corrosion potential from-0.421 6 V to-0.282 1 V and a reduction in corrosion current density from 4.809× 10-7 A/cm2 to 1.475× 10-7 A/cm2.Long-term immersion tests further confirmed the superior corrosion resistance of the laser-remelted coating compared to the plasma-sprayed coating.The improved performance is attributed to the elimination of large pores and visible cracks that characterized the surface of the sprayed coating.These defects allowed electrolyte penetration to the coating-substrate interface,facilitating electrochemical reactions.Additionally,electrolyte infiltration led to significant Cl-aggregation within the pores,hindering the formation of a protective passive film on the sprayed coating's surface.Laser remelting addressed these issues by effectively sealing the pores and cracks,enabling the formation of a uniform and dense passivation film that significantly impedes electrolyte penetration.The process of combining plasma spraying with laser remelting produces HEA coatings with fewer defects and enhanced corrosion resistance,offering valuable insights for broadening the application of HEAs in various industries.
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