氧化物增强CoCrNi中熵合金的微观组织和力学、摩擦学性能研究

中、高熵合金自2004年被首次提出以来一直备受关注，成为金属材料的研究前沿。其中，针对面心立方结构（FCC）中熵合金强度不足的问题，研究学者们开展了大量研究，提出了许多有效的强化方式，但仍未实现强度、塑性和耐磨性的有机统一。基于此，本研究结合晶界强化和氧化物弥散强化原理，设计和制备了一种新型的高强、高耐磨并具有一定塑性的CoCrNi合金，系统研究了其制备工艺、微观组织和力学、摩擦学性能。 本课题通过在CoCrNi合金中加入Ti 和Y两种元素形成氧化物弥散强化中熵合金，利用“机械合金化+放电等离子体烧结”工艺制备超细晶合金。采用加入Y2O3颗粒粉末非原位形成氧化物强化和加入纯Y元素粉末原位形成氧化物强化两种方式研究氧化物弥散强化CoCrNi合金的组织和性能。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、电子背散射衍射（EBSD）和透射电子显微镜（TEM）等表征设备系统地研究了这两种合金的微观组织，结果表明这两种合金均形成了超细晶组织，其平均晶粒尺寸分别为385 nm和282 nm，同时在合金内部形成了大量的Y-Ti-O纳米析出相。室温拉伸试验表明，加入Ti和Y元素形成的氧化物弥散强化CoCrNi合金具有很高的屈服强度，同时还保留有一定的塑性，特别是加入纯Y元素粉末原位形成氧化物强化的CoCrNi合金其屈服强度高达1660 MPa。本研究定量分析了原位形成氧化物强化合金的强化机制，结果表明该合金的高强度主要源于纳米析出相弥散强化和晶界强化。 此外，本课题亦系统研究了两种不同制备方法得到的合金在室温和600℃下的摩擦磨损性能，实验结果表明这两种合金在室温和600℃均具有良好的耐磨性能，与氮化硅对磨时其磨损率在10-5 mm3/(N·m)量级。同时利用3D轮廓仪、SEM和能谱（EDS）等分析表征了磨损表面以及磨屑的形貌和元素成分，发现这两种合金在室温下主要磨损机制为磨粒磨损，600℃下主要为氧化磨损。

Since it was first proposed in 2004, the medium entropy alloy and high entropy alloy have attracted much attention and become the research frontier of metal materials. Considering the lack of strength of medium-entropy alloy with face-centered cubic structure (FCC), researchers have carried out a lot of research and proposed many effective strengthening methods, but the organic unity of strength, plasticity and wear resistance has not been achieved. Based on this, a new type of CoCrNi alloy with high strength along with certain plasticity and high wear resistance was designed and prepared by combining the principle of grain boundary strengthening and oxide dispersion strengthening. The preparation process, microstructure, mechanical and tribological properties of CoCrNi alloy were systematically studied. In this study, two elements, Ti and Y, were added into the CoCrNi alloy to form an oxide dispersion strengthened medium entropy alloy, and the process of "Mechanical Alloying + Spark Plasma Sintering" was used to prepare ultra-fine grain alloy. The microstructure and properties of CoCrNi alloy strengthened by oxide dispersion were studied by adding Y2O3 particle powder and adding pure Y element powder. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructure of the two alloys. The results show that the microstructure of the two alloys is ultrafine, and the average grain size is 385 nm and 282 nm, respectively. At the same time, a large number of Y-Ti-O nano precipitates are formed in the alloy. The tensile test at room temperature shows that the oxide dispersion strengthened CoCrNi alloy formed by adding Ti and Y elements has a high yield strength, but also retains a certain plasticity. Especially, the yield strength of CoCrNi alloy strengthened by adding pure Y element powder in situ is up to 1660 MPa. In this study, the strengthening mechanism of in-situ oxide strengthening alloy was quantitatively analyzed. The results show that the high strength of the alloy is mainly due to the dispersion strengthening of nano precipitates and grain boundary strengthening. In addition, the tribological properties of the alloys prepared by two different methods were also systematically studied at room temperature and 600℃. The experimental results show that the two alloys have good wear resistance at room temperature and 600℃, and the wear rate of the two alloys is in the order of 10-5 mm3/(N·m) when grinding against silicon nitride. At the same time, 3D profilometer, SEM and energy dispersive spectroscopy (EDS) were used to analyze and characterize the microstructure and elemental composition of the worn surface and wear debris. It was found that the main wear mechanism of the two alloys were abrasive wear and slight oxidation wear at room temperature, and the main wear mechanism was oxidation wear at 600℃.