【作者】 罗涛；

【导师】 陈刚； 刘国跃；

【作者基本信息】 湖南大学 ， 材料工程（专业学位）， 2021， 硕士

【摘要】 近年来,高熵合金（High entropy alloys,HEAs）作为一个新的合金设计理念,由于成分、结构和性能具有可调性而成为了金属材料领域中的研究热点,在航空航天、石油化工、汽车制造、电子电气等领域具有广阔的应用前景。目前,高熵合金及高熵合金基复合材料的制备工艺大多采用熔炼法和粉末冶金法,这两种制备技术的复杂性及高成本在一定程度上限制了高熵合金及其复合材料的实际应用,因此,开发一种高效快捷、低成本的合金制备方法有利于促进高熵合金的研究与发展。本文将铝热法应用到高熵合金及高熵合金基复合材料的制备中。首先对多主元合金进行成分调控研究,基于Fe₃O₄、Co₂O₃、Ni₂O₃、Mn O₂和Cr O₃五种氧化物经铝热反应后生成Co-Cr-Fe-Ni-Mn系26种合金,探究了多种不同氧化物铝热反应的负焓值与铝热还原产物成分之间的对应关系,进而推广到多种氧化物铝热反应的负焓值与反应后成分之间的一般规律,拟合出对应的函数关系式,并基于此制备了近似等摩尔比的CoCrFeNiMnAl高熵合金,从而实现对铝热法制备多主元高熵合金的成分的调控。在此基础上,制备了近等摩尔比的（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）系列高熵合金,探究W含量对CoCrFeNiMnAl高熵合金的相结构、微观组织和性能的影响。结果表明,（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）高熵合金均以FCC+BCC相结构组成,微观组织均为枝晶和枝晶间结构。随着W含量的增加,该合金的维氏硬度从533.2 HV提高到604.6 HV,耐磨损性能也相应的提高,CoCrFeNiMnAl_97.0W_3.0合金的摩擦系数和磨损率分别为0.684和1.06×10^-5mm³/N·m,磨损机制由粘着磨损转变为粘着磨损和磨粒磨损相结合,最后再转变为磨粒磨损。（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）高熵合金在3.5wt%Na Cl溶液中的耐腐蚀性能随着W含量的增加而提高,腐蚀电流密度从6.08×10^-6 A/cm²减小到1.72×10^-6 A/cm²,腐蚀速率逐渐减小。进一步地,增大W的含量以及优化高熵合金成分,原位生成了W/FeNiMnAlW高熵合金基复合材料,高熵合金基体由FCC相、B2相和W₂C相组成。增强相W颗粒均匀分布在基体组织中,其体积分数和平均晶粒尺寸分别为30.9%和13.57μm,与基体实现良好的冶金结合。W相、B2相和FCC相的硬度分别为681.48HV、533.82 HV和286.70 HV。W/FeNiMnAlW复合材料的屈服强度为1241 MPa,最大抗压强度和最大塑性应变分别超过2530 MPa和15%,表现出良好的力学性能。W/FeNiMnAlW复合材料的体积磨损量和磨损率分别为0.42 mm³和4.95×10^-3mm³/N·m,磨损机理主要为粘着磨损和磨粒磨损。该复合材料在3.5wt%Na Cl溶液中的腐蚀电位和腐蚀电流密度分别为-0.505 V_sce和1.002×10^-5A/cm²。分析认为W颗粒呈近球型均匀分布以及FCC相与B2相的有效结合是该复合材料具有良好性能的主要原因。更多还原

【Abstract】 In recent years,high-entropy alloys（HEAs）,as a new alloy design concept,has become a research hotspot in the field of metal materials due to its adjustable composition,structure and properties,which has a broad application prospect in aerospace,petrochemical,automobile manufacturing,electronics and electrical fields.At present,the preparation processes of high-entropy alloys and high-entropy alloy matrix composites mostly use smelting and powder metallurgy methods.The complexity and high cost of these two preparation technologies limit the practicality application of high-entropy alloys and their composites to a certain extent.Therefore,the development of an efficient,fast,and low-cost alloy preparation method is conducive to promoting the research and development of high-entropy alloys.In this paper,the thermite method was applied to the preparation of high-entropy alloys and high-entropy alloy matrix composites.Firstly,the composition control of multi-principal alloys is studied.Based on the five oxides of Fe₃O₄,Co₂O₃,Ni₂O₃,Mn O₂ and Cr O₃,26 alloys of the Co-Cr-Fe-Ni-Mn series are formed after thermite reaction.The corresponding relationship between the negative enthalpy of the thermite reaction of a variety of different oxides and the composition of the thermite reduction products was investigated.The general law between the negative enthalpy value of various oxides of thermal reaction and the composition after reaction is extended,and the corresponding functional relations are put forward.Based on this,a CoCrFeNiMnAl high-entropy alloy with approximately equimolar ratio was prepared,so as to realize the control of the composition of multi-principal element high entropy alloy prepared by thermite method.On this basis,the（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）series high-entropy alloys with nearly equimolar ratio were prepared,and the effect of W content on the phase structure,microstructure and properties of CoCrFeNiMnAl high-entropy alloys was explored.The results show that（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）high-entropy alloys are composed of FCC+BCC phase structure,and the microstructures are all dendrite and interdendritic structure.With the increase of W content,the Vickers hardness of the alloy increases from 533.2 HV to 604.6 HV,and the wear resistance is also improved accordingly.The friction coefficient and wear rate of the CoCrFeNiMnAl_97.0W_3.0 alloy are 0.684 and 1.06×10^-5 mm³/N·m,respectively,the wear mechanism changes from adhesive wear to a combination of adhesive wear and abrasive wear,and finally to abrasive wear.The corrosion resistance of（CoCrFeNiMnAl）_100-xW_x（x=2.0,2.5,3.0）high-entropy alloy in 3.5wt%Na Cl solution increases with the increase of W content,and the corrosion current density is from6.08×10^-6 A/cm² Reduce to 1.72×10^-6 A/cm²,the corrosion rate gradually decreases.Furthermore,the content of W increased and the composition of high entropy alloy optimized,W/FeNiMnAlW high-entropy alloy matrix composite material was prepared by in-situ.The high-entropy alloy matrix was composed of FCC phase,B2 phase and W₂C phase.The reinforcing phase W particles are uniformly distributed in the matrix structure,and their volume fraction and average grain size are 30.9%and 13.57μm,respectively,and the tungsten particles form a good metallurgical bond with the matrix.The hardness of W phase,B2 phase and FCC phase are 681.48 HV,533.82 HV and286.70 HV,respectively.The yield strength of W/FeNiMnAlW composite is 1241 MPa,and the maximum compressive strength and the maximum plastic strain are more than2530 MPa and 15%,respectively,showing good mechanical properties.The volumetric wear and wear rate of W/FeNiMnAlW composites are 0.42 mm³ and 4.95×10^-3mm³/N·m,respectively.The wear mechanisms are mainly adhesive wear and abrasive wear.The corrosion potential and corrosion current density of the composite in 3.5wt%Na Cl solution are-0.505 Vsce and 1.002×10^-5 A/cm²,respectively.The analysis suggests that the nearly spherical uniform distribution of W particles and the effective combination of FCC phase and B2 phase are the main reasons for the good performance of the composites.更多还原