【作者】 李丽；

【导师】 姜慧；

【作者基本信息】 山东科技大学 ， 机械工程， 2023， 硕士

【摘要】 共晶高熵合金基复合材料不仅具有共晶高熵合金良好的铸造性能、可控微观结构、高的热稳定性、高强度和高塑性、耐磨性能等,还具有金属基复合材料高比强度、比模量等特点,在摩擦磨损材料领域具有很高的实际应用潜力。当前,进一步提高该类材料的磨损性能是推动其工业化应用的关键。为此,本研究从增强体和制备方法两方面着手,以具有FCC（Ll₂）+BCC（B2）结构的双相AlCoCrFeNi_2.1共晶高熵合金为基体,选择NbC陶瓷颗粒和Ni₃Al金属颗粒作为增强体,分别采用粉末冶金和激光熔覆两种方法制备出高性能颗粒增强共晶高熵合金基复合材料。系统研究了颗粒增强体和制备方法对AlCoCrFeNi_2.1共晶高熵合金基复合材料微观组织和性能的影响规律,并揭示其磨损机制,建立材料宏观性能与其微观组织间的内在联系。主要研究结论如下:（1）通过粉末冶金方法制备出AlCoCrFeNi_2.1-x NbC（x=0,2.5,7.5,10wt.%）共晶高熵合金基复合材料块体,结果发现:随着NbC颗粒含量的添加,AlCoCrFeNi_2.1-x NbC复合材料相结构由B2+FCC两个主要相和Al₂O₃和Cr₇C₃两个次要相转变为NbC+FCC两个主要相和Al₂O₃和Cr₇C₃两个次要相;且添加2.5、7.5、10wt.%NbC复合材料中析出的NbC颗粒呈微/纳米尺寸的双尺度分布。所有的复合材料均表现出较高的维氏硬度,分别为675HV0.5（x=0）、660HV0.5（x=2.5）、685HV0.5（x=7.5）和700HV0.5（x=10）;随着NbC颗粒含量的增加,AlCoCrFeNi_2.1-x NbC复合材料的平均摩擦系数从0.59逐渐减小到0.42,磨损率首先从1.5×10^-5mm³N^-1m^-1增加到1.7×10^-5mm³N^-1m^-1,然后降低到2.4×10^-6mm³N^-1m^-1。其中AlCoCrFeNi_2.1-10NbC共晶高熵合金基复合材料表现最优的耐磨性能,其磨损机制主要为氧化磨损。（2）AlCoCrFeNi_2.1-x Ni₃Al（x=0,5.0,7.5,10wt.%）共晶高熵合金基复合材料块体呈现出FCC/Ll₂和B2相以及少量的Al₂O₃和Cr₇C₃相构成的胞状网格结构。随着Ni₃Al颗粒含量的增加,AlCoCrFeNi_2.1-x Ni₃Al复合材料的平均摩擦系数从0.72降低到0.40,磨损率先从2.6×10^-5mm³N^-1m^-1增加到2.7×10^-5mm³N^-1m^-1再降低到4.9×10^-6mm³N^-1m^-1;压缩断裂强度整体上从1700MPa增加到2301MPa,压缩塑性从7.0%提升到10.1%,压缩屈服强度从屈服之前断裂提升到1845MPa。其中,AlCoCrFeNi_2.1-10Ni₃Al共晶高熵合金基复合材料表现最优的综合力学性能与耐磨性能,其磨损机制主要为磨粒磨损。（3）采用激光熔覆方法在H13钢基体分别制备出NbC/Ni₃Al颗粒增强AlCoCrFeNi_2.1共晶高熵合金基复合材料涂层。AlCoCrFeNi_2.1-x NbC（x=0,2.5,5.0,7.5,10wt.%）共晶高熵合金基复合材料涂层均由NbC相、FCC/Ll₂相和BCC相构成;随着NbC颗粒含量的增加,NbC相数量增多、分布均匀且形貌逐渐从棒状转变成不规则多面体。AlCoCrFeNi_2.1-x NbC共晶高熵合金基复合材料涂层的硬度值从270HV0.5增加到365HV0.5（硬度值相当于H13基体的2倍）;AlCoCrFeNi_2.1-x NbC复合材料涂层的平均摩擦系数和磨损体积都有明显的降低。当x=5.0wt.%时,复合材料涂层的耐磨性能最优,摩擦系数和磨损体积分别为0.59和3.96×10⁶μm³,磨损机制主要为氧化磨损和磨粒磨损并伴随着轻微的疲劳磨损。AlCoCrFeNi_2.1-x Ni₃Al（x=0,2.5,5.0,7.5,10wt.%）共晶高熵合金基复合材料涂层均由FCC/Ll₂相和BCC相构成。随着Ni₃Al含量的增加,BCC相体积分数先增加后减少直至消失,而Ll₂析出相体积分数先减小后增加且分布均匀;AlCoCrFeNi_2.1-x Ni₃Al复合材料涂层硬度从270HV0.5增加到425HV0.5（硬度值相当于H13基体的2.2倍）。当x=10wt.%时,复合材料涂层的耐磨性能最佳,摩擦系数和磨损体积分别为0.513和6.50×10⁶μm³,其磨损机制主要为氧化磨损并伴随着少量磨粒磨损。更多还原

【Abstract】 Eutectic high entropy alloy（EHEA）matrix composites have good casting properties,controlled microstructure,high thermal stability,high strength and plasticity,wear resistance and other excellent properties,also have high specific strength and specific modulus of metal matrix composites,showing great potential for practical applications in the field of friction wear materials.Currently,the key factor for promoting its industrial application is further to optimize wear properties.Therefore,the high performance particle reinforced EHEA matrix composite was prepared by both powder metallurgy and laser cladding method,which composed of dual-phase AlCoCrFeNi_2.1 EHEA with FCC（Ll₂）+BCC（B2）structure as the matrix and NbC/Ni₃Al metal particles as the reinforcement.The influence of the particle reinforcement and preparation method on the microstructure and properties of the AlCoCrFeNi_2.1EHEA matrix composites is systematically investigated.And its wear mechanism is revealed.In addition,for the AlCoCrFeNi_2.1EHEA matrix composites,intrinsic relationship between the macroscopic mechanical propertiesr and microstructure will be established.The main research findings are as follows:（1）AlCoCrFeNi_2.1-x NbC（x=0,2.5,7.5,10wt.%）EHEA matrix composites blocks were prepared by powder metallurgy method.The results found that with the addition of NbC particle content,the phase structure of AlCoCrFeNi_2.1-x NbC composites changed from two major phases of B2+FCC,and two minor phases of Al₂O₃ and Cr₇C₃ to two major phases of NbC+FCC and two minor phases of Al₂O₃ and Cr₇C₃.And the NbC particles precipitated with the addition 2.5、7.5、10wt.%NbC composites showed a dual-scale distribution of micro/nano sizes.All composites exhibit high Vickers hardness of 675HV0.5（x=0）、660HV0.5（x=2.5）、685HV0.5（x=7.5）and700HV0.5（x=10）.With increasing NbC particle content,the average friction of the AlCoCrFeNi_2.1-x NbC composites gradually decreased from 0.59 to 0.42,and the wear rate first increased from 1.5×10^-5mm³N^-1m^-1 to 1.7×10^-5mm³N^-1m^-1 and then decreased to 2.4×10^-6mm³N^-1m^-1.Wherein,the AlCoCrFeNi_2.1-10NbC EHEA matrix composites showed the best wear resistance,and the wear mechanism was mainly oxidation wear.（2）The AlCoCrFeNi_2.1-x Ni₃Al（x=0,5.0,7.5,10wt.%）EHEA matrix composites exhibit a cellular lattice structure consisting of FCC/Ll₂ and B2 phases and small amounts of Al₂O₃ and Cr₇C₃ phases.With the Ni₃Al particle content increases,the average friction coefficient of the AlCoCrFeNi_2.1-x Ni₃Al composites decreased from 0.72 to 0.40,the wear rate first increased from2.6×10^-5mm³N^-1m^-1 to 2.7×10^-5mm³N^-1m^-1 and then decreased to 4.9×10^-6mm³N^-1m^-1.The overall compression fracture strength increased from 1700MPa to 2301MPa,the compressive plasticity increased from 7.0%to 10.1%,and the compression yield strength increased from fracture before yield to 1845MPa.Wherein,the AlCoCrFeNi_2.1-10Ni₃Al EHEA matrix composite exhibits the best comprehensive mechanical properties and wear resistance properties,and its wear mechanism is mainly abrasive wear.（3）The NbC/Ni₃Al particle reinforced AlCoCrFeNi_2.1 EHEA matrix composites were prepared separately by laser cladding on H13 steel substrates.AlCoCrFeNi_2.1-x NbC（x=0,2.5,5.0,7.5,10wt.%）EHEA matrix composites are composed of NbC、FCC/Ll₂ and BCC phases.With increasing NbC particle content,the number of NbC phase increases,the distribution becomes homogeneous and the morphology gradually changes from rod-like to irregular polyhedra.The hardness values of the AlCoCrFeNi_2.1-x NbC EHEA matrix coatings increase from 270HV0.5 to365HV0.5（twice the hardness value of the H13 matrix）.The average friction coefficient and wear volume of the AlCoCrFeNi_2.1-x NbC composite coating decreased significantly.When x=5.0wt.%,the composite coating has the best wear resistance,and the friction coefficient and wear volume are 0.59 and 3.96×10⁶μm³,respectively.The wear mechanism is mainly oxidative wear and abrasive wear accompanied by slight fatigue wear.The AlCoCrFeNi_2.1-x Ni₃Al（x=0,2.5,5.0,7.5,10wt.%）EHEA matrix composite coatings are composed of FCC/Ll₂ and BCC phases.With increasing Ni₃Al particle content,the volume fraction of BCC phase increases and then decreases until it disappears,while the volume fraction of Ll₂ precipitated phase with uniform distributed decreases and then increases.The hardness of the AlCoCrFeNi_2.1-x Ni₃Al composite coating increases from 270HV0.5 to 425HV0.5（2.2 times the hardness value of the H13 matrix）.When x=10wt.%,the composite coating has the best wear resistance,with friction coefficient and wear volume of 0.513 and 6.50×10⁶μm³,and the wear mechanism being mainly oxidative wear and accompanied by abrasive wear.更多还原