激光重熔对等离子喷涂AlCoCrFeNi高熵合金涂层组织和耐腐蚀性能的影响

Effect of Laser Remelting on Microstructure and Corrosion Resistance of Plasma Sprayed AlCoCrFeNi High-entropy Alloy Coating

现有关于高熵合金涂层重熔处理的研究大多集中在涂层的组织结构、力学性能和耐磨损性能等方面,对其耐腐蚀性能的研究较少。为了揭示激光重熔对高熵合金涂层耐腐蚀性能的影响,采用等离子喷涂技术在AISI 1045钢表面制备AlCoCrFeNi高熵合金涂层,并采用激光重熔工艺对其进行重熔处理,对重熔前后涂层的组织结构和耐腐蚀性能进行对比研究。结果表明:激光重熔基本消除了喷涂层中的孔隙和裂纹等缺陷,涂层与基体之间由机械结合转变为冶金结合;重熔层由BCC固溶体相和少量FCC析出相组成,组织形态呈树枝晶状。极化曲线和电化学阻抗谱分析表明,激光重熔可以改善AlCoCrFeNi高熵合金涂层在3.5%NaCl溶液中的耐腐蚀性能。激光重熔后,涂层的自腐蚀电位从-0.421 6 V增加到-0.282 1 V,腐蚀电流密度从4.809×10^(-7)A/cm^(2)降低到1.475×10^(-7)A/cm^(2)。长期浸泡腐蚀试验也表明重熔层的耐腐蚀性能要显著优于喷涂层。通过等离子喷涂结合激光重熔技术得到缺陷较少、耐腐蚀性较好的高熵合金涂层,对于高熵合金的广泛应用具有重要的参考价值。

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–0.4216 V to–0.2821 V and a reduction in corrosion current density from 4.809×10^(-7)A/cm^(2) to 1.475×10^(-7)A/cm^(2).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.