【作者】 李娟；

【导师】 王彦芳；

【作者基本信息】 中国石油大学(华东) ， 材料科学与工程， 2020， 硕士

【摘要】 高熵合金由于动力学上的延迟扩散效应、结构上的晶格畸变效应、热力学上的高熵效应以及性能上的“鸡尾酒”效应,展现出了优异的力学性能、摩擦磨损性能、耐腐蚀性和耐高温等性能。同时由于合金元素种类多,且近排异种原子造成d带配位效应及晶格应力现象,使其表现出独特的催化活性,在能源、催化领域具有广阔的应用前景。本文采用电弧熔炼法制备铸态FeCoNiCrAl_x高熵合金（x=0.5,0.6,1,1.5,2,2.5,3）,并对其进行不同温度真空退火处理。利用X射线衍射仪（XRD）、光学显微镜（OM）、能谱仪（EDS）、扫描电子显微镜（SEM）、电化学工作站和显微硬度计等研究合金在退火处理前后的相组成、显微组织、电化学腐蚀行为和硬度等性能。采用高能砂磨机将退火后的高熵合金样品制备成粉末,采用Na OH进行去合金化处理,并运用SEM、激光粒度分析仪及比表面积及孔径分析仪等分析了去合金化前后高熵合金粉末的微观形貌、粒度、比表面积及孔径的分布和N₂吸附特性。研究表明,随着Al含量的增加,铸态FeCoNiCrAl_x高熵合金（x=0.5,0.6,1,1.5,2,2.5,3）由单一FCC结构逐渐转变为FCC+BCC结构和单一BCC结构,并出现有序化。铸态组织由粗大树枝晶逐渐变为纤维状、细小树枝晶状和等轴枝晶。在热处理过程中,FeCoCrNiAl₂的B2相不断增加,FeCoCrNiAl_0.5和FeCoCrNiAl_0.6在600℃10 h热处理后BCC相增加,经过1000℃热处理后BCC相均消失。热处理过程中合金的硬度均先增加后减小。随着退火温度的升高,FeCoCrNiAl_0.5和FeCoCrNiAl_0.6的耐蚀性先降低后增加,FeCoCrNiAl₂耐蚀性逐渐降低,铸态下耐蚀性最好。采用高能砂磨方法制备的粉末仍保持原物相结构。随着砂磨时间增长,粉末不断细化,继续砂磨,粉末出现片化。随Al含量的增加,粉末达到最佳粒度所需砂磨时间逐渐缩短,高熵合金粉末最佳粒度逐渐变细,FeCoNiCrAl_x（x=1,1.5,2,2.5,3）平均粒径分别为57.5μm,22.2μm,22.0μm,21.9μm和9.8μm,分选系数分别为5.9,4.7,4.5,3.7和2.7。粉末表面光滑,形状规整。采用10%的Na OH溶液对高熵合金粉末进行去合金化处理,反应时间60 min,搅拌速度800 r/min,剂碱比为1:10,反应温度80℃。去合金化化处理后的粉末分散良好,没有明显团聚现象,等温线为Ⅳ型,为典型的介孔结构。去合金化可有效提高高熵合金粉末的比表面积,其中FeCoCrNiAl₃中去合金化后比表面积增大1.5倍,达139.3m²/g。更多还原

【Abstract】 Due to the delayed diffusion effect on dynamics,lattice distortion effect on structure,high entropy effect on thermodynamics and"cocktail"effect on properties,the high entropy alloy exhibits excellent mechanical properties,friction and wear properties,corrosion resistance and high temperature resistance.At the same time,due to the varieties of elements,the d-band coordination effect and lattice stress caused by the close rejection of different atoms,it shows a unique catalytic activity,which has a broad application prospect in the fields of energy and catalysis.The as-cast FeCoNiCrAl_x high entropy alloy（x=0.5,0.6,1,1.5,2,2.5,3）was prepared by arc smelting,and the alloy was annealed at different temperatures.The phase composition,microstructure,electrochemical corrosion behavior and hardness properties of the alloy before and after annealing were studied by means of X-ray diffraction（XRD）,Optical Microscope（OM）,EDS,SEM,electrochemical workstation and microhardness tester.The annealed alloy was prepared into micron powder in the way of sand-milling,Na OH was used to broaden the specific surface of the powder.SEM,laser particle size analyzer,specific surface and pore size analyzer were used to analyze the micro morphology,particle size,specific surface,pore size,and N₂ adsorption properties of the high entropy alloy powder before and after dealloying.The study showed that with the increase of Al content,the as-cast FeCoNiCrAl_x high entropy alloy（x=0.5,0.6,1,1.5,2,2.5,3）gradually changed from FCC structure to FCC+BCC structure and BCC structure,and the structure became orderly.The as-cast structure changed from thick dendritic to fibrous,fine dendritic and equiaxial dendrite.In the heat treatment process,the B2 phase of FeCoCrNiAl₂ increased continuously,the BCC phase of FeCoCrNiAl_0.5 and FeCoCrNiAl_0.6 increased after the heat treatment at 600℃for 10h,and then disappeared after heat treatment at 1000℃.In the process of heat treatment,the hardness of the alloy increases first and then decreases.With the increase of annealing temperature,the corrosion resistance of FeCoCrNiAl_0.5 and FeCoCrNiAl_0.6 first decreased and then increased.The corrosion resistance of FeCoCrNiAl₂ gradually decreased,the best corrosion resistance is under the cast state.With the sand-milling,the high entropy alloy still keeps the original structure,and the powders are refined continuously.With the increase of Al content,the required time to get the best powder is gradually reduced,and the high entropy alloy powder is gradually finer.FeCoNiCrAl_x（x=1,1.5,2,2.5,3）had an average particle size of 57.5μm,22.2μm,22.0μm,22.0μm and 9.8μm,and the sorting coefficients were 5.9,4.7,4.5,3.7,and 2.7.The surface of the powder is smooth,and the particle size distribution is even.The high-entropy alloy powder was dealloyed with 10%Na OH solution at 80℃.The reaction time was 60mins,the stirring speed was 800r/min,the ratio of agent to base was 1:10.After dealloying,the surface of the high entropy alloy is well distributed and has no obvious agglomeration.The isotherm obtained by the test is type IV,which is a typical mesoporous structure.Dealloying effectively improves the specific surface area of high-entropy alloy powder,among which,the specific surface area of FeCoCrNiAl₃ increased by 1.5 times after dealloying,reaching 139.3 m²/g.更多还原