激光熔覆AlCoCrFeNiCu高熵合金工艺优化及耐蚀性研究

Process Optimization and Corrosion Resistance of Laser Cladding AlCoCrFeNiCu High-entropy Alloy

目的通过脉冲Nd:YAG固体激光器在Q235钢表面熔覆AlCoCrFeNiCu高熵合金涂层,改善其表面性能。方法采用正交实验法优化激光熔覆工艺参数,通过X射线衍射仪、扫描电子显微镜(SEM)及能谱仪(EDS)、显微硬度仪分析涂层的物相组成、显微组织、元素成分以及硬度分布。采用三电极体系对高熵合金涂层的极化性能以及电化学阻抗谱(EIS)进行测试,研究高熵合金涂层在质量分数为3.5%的NaCl溶液中的腐蚀行为。结果以稀释率和硬度为响应并进行极差和方差分析,最终得出的最佳工艺参数如下:铺粉厚度为1.25 mm,扫描速度为180 mm/min,电流大小为220 A,离焦量为-7 mm。高熵合金涂层物相由富Cu的FCC相以及富(Al,Ni)的BCC相双相构成。表层微观组织为细小、均匀的等轴晶,中部为粗大的柱状树枝晶,涂层底部与基体结合处出现明显的平面晶。Cu元素在枝晶间出现轻微偏析。涂层最高硬度达到521HV0.2,是基体的2.7倍。在质量分数为3.5%的NaCl溶液中,AlCoCrFeNiCu高熵合金涂层较基体有更正的自腐蚀电位、更小的自腐蚀电流密度、更大的容抗弧半径以及阻抗模值,表现出良好的耐蚀性。结论激光熔覆技术制得的高熵合金涂层成形良好、性能优异,AlCoCrFeNiCu高熵合金涂层能有效提高基体耐蚀性,起到保护作用。

This paper aims to optimize the surface mechanical properties of Q235 steel by cladding the AlCoCrFeNiCu high-entropy alloy coating by pulsed Nd:YAG solid-state laser.Orthogonal experiment method is proposed to optimize laser cladding process parameters,and the X-ray diffractometer,scanning electron Microscope(SEM),energy spectrometer(EDS),Microhardness tester were carried out to analyze the phase composition,microstructure,element composition and hardness distribution of the coating.A three-electrode system was used to test the polarization performance and electrochemical impedance spectroscopy(EIS)of the high-entropy alloy coating to study its corrosion resistance in 3.5wt.%NaCl solution.The results taking dilution rate and hardness as response to analyze its range and variance,and the optimal process parameters were obtained as coating thickness of 1.25 mm,scanning speed of 180 mm/min,current size of 220 A,and defocus amount of−7 mm.The Cu-rich FCC phase and the(Al,Ni)BCC phase constitute the high-entropy alloy coating phase.The Cu element segregates between the dendrites.The microstructure of the surface layer is fine and uniform equiaxed crystals,the middle part is thick columnar dendrites,and the plane crystals can be observed at the junction between the bottom of the coating and the substrate obviously.Furthermore,the maximum hardness of the coating reaches 521HV0.2,which is 2.7 times that of the substrate.In 3.5wt.%NaCl solution,the high entropy alloy coating of AlcoCrFeNiCu shows good corrosion resistance than the substrate with a more positive self-corrosion potential,smaller self-corrosion current density,larger reactance arc radius and impedance film value.In conclusion,the laser cladding technology can produce high-entropy alloy coatings with good forming and performance,and the AlCoCrFeNiCu high-entropy alloy coating can protect the substrate by effectively improve the corrosion resistance.