等离子熔覆制备AlCrFeMnNi高熵合金涂层的微观组织与性能

Microstructure and Properties of an AlCrFeMnNi High-entropy Alloy Coating Prepared Using Plasma Cladding

对高熵合金涂层的成分设计已有较多探究,但针对无Co系高熵合金涂层研究较少。采用等离子熔覆技术在E32钢上制备AlCrFeMnNi高熵合金涂层,利用金相显微镜、SEM、EDS、XRD等对涂层的组织形貌、相结构及元素分布等进行观察分析,采用显微硬度计、电化学工作站、XPS表征涂层的硬度分布及耐腐蚀性能。结果表明,等离子熔覆制备的高熵合金涂层无裂纹、气孔等宏观缺陷,涂层为BCC结构;涂层平均硬度为411.6 HV0.5,为基体硬度的2倍以上;在质量分数3.5%的NaCl溶液中涂层的自腐蚀电位为-0.35V,自腐蚀电流密度为507 nA/cm^(2),基体的自腐蚀电位为-0.92V,自腐蚀电流密度为256μA/cm^(2),涂层的自腐蚀电位和极化电流密度较基体有大幅度提升,涂层的固溶强化作用和晶格畸变作用以及BCC结构的螺旋位错强化是提升涂层硬度的原因,均匀的元素分布和致密的钝化膜是其耐蚀性好的主要原因。通过等离子熔覆技术得到高强度、耐腐蚀性好无Co系高熵合金的涂层,可对易制备、低成本的高熵合金涂层的开发、制备和应用提供一定的技术支持。

Compared with traditional alloys,high-entropy alloys(HEAs)with simple structures exhibit good mechanical properties and low corrosion resistance.These unique properties indicate that HEAs can be applied in extreme environments such as high temperatures,high corrosion,and high wear.However,common HEAs contain expensive and rare metals,which limit their large-scale application.Because pure metals can no longer satisfy the requirements of future development,an HEA@metal composite composed of a protective coating of HEA on a metal matrix,in which the HEA act as reinforcement,is expected to enhance their performance.To date,many reports have focused on revealing the reinforcement mechanism of HEA coatings with Co;however,few studies have focused on HEA coatings without Co.In this study,we successfully prepared a series of AlCrFeMnNi HEA coatings on an E32 steel matrix using a plasma cladding technique.The effects of composition and structure on the HEA@metal composites were studied.X-ray diffraction,metallographic microscopy,scanning electron microscopy,energy dispersive spectroscopy,and microhardness tests were used to characterize the distribution of the elements,microstructure phase,and hardness of the coatings.In addition,potentiodynamic polarization curves,electrochemical impedance spectroscopy,and immersion experiments were performed for a 3.5%NaCl solution using an electrochemical workstation to determine the corrosion resistance performance.Finally,X-ray photoelectron spectroscopy was performed on the soaked coatings to analyze the passive film formation.The results showed that the AlCrFeMnNi HEA coating prepared using plasma cladding had a BCC structure,which was consistent with the HEA particles used in this study.No macroscopic defects,such as cracks and pores,occurred at the interface between the HEA coating layer and the metal matrix,indicating good metallurgical bonding.Because of the dilution of the substrate,the Fe content in the AlCrFeMnNi HEA coating increased considerably,and the microstructure of the AlCrFeMnNi HEA coating changed from columnar dendrites to coarse equiaxed crystals,indicating that an increase in Fe content has a significant effect on the microstructure of the AlCrFeMnNi HEA coating.The average hardness of the coating was 411.6 HV0.5,which was twice that of the substrate.The enhancement of the hardness can be summarized as follows:First,the disordered atomic distribution of the HEA coating can significantly increase the solid-solution strengthening and lattice distortion of the coating,thus resulting in superior hardness of the coating.Second,the intrinsic helical dislocations in the BCC structure can significantly increase the hardness of the HEA coating.In addition,the rapid cooling process during plasma cladding positively influence the hardness of the coating.In 3.5 wt.%NaCl solution,the self-corrosion potential of the AlCrFeMnNi HEA coating was−0.35 V and the self-corrosion current density was 507 nA/cm^(2).In comparison,the self-corrosion potential and current density of the substrate were−0.92 V and 256μA/cm^(2),respectively.Both the self-corrosion potential and polarization current density of the coating increased significantly compared with those of the substrate,demonstrating excellent corrosion resistance.The uniform distribution of elements and dense passive film were the main reasons for its superior corrosion resistance.Although the AlCrFeMnNi HEA coating exhibited excellent hardness and corrosion resistance,the uncertainty caused by the dilution of the matrix considerably increased the uncertainty of the structure and properties of the HEA coating.Thus,the contingency resulting from the dilution of the matrix must be explored further.Consequently,plasma cladding a non-Co HEA onto a metal matrix can enhance strength and corrosion resistance.This study provides technical support for the development and application of large-scale and low-cost high-entropy alloy coatings.