含CoCrFeNi高熵合金的结构调控和性能提升

发布时间：2018-05-26 15:17

本文选题：高熵合金 + 预形变　；参考：《济南大学》2017年硕士论文

【摘要】：高熵合金打破了传统合金配比理念,通常采取等原子比或近等原子比方式制备新型合金,因其全新的设计理念、独特的结构和优异的力学性能、良好的耐蚀性、耐磨性及电磁学性能,引起了广泛的研究兴趣,具有广阔的前景。本课题采用电弧熔炼法制备CoCrFeNi、CoCrFeNiWx和CoCrFeNi Mox(x=0.2,0.5)高熵合金,利用X射线衍射仪,差示扫描量热仪,场发射扫描电镜,电化学工作站、显微硬度计和MTS万能试验机等分析和测试手段研究预形变处理及元素添加对含CoCrFeNi高熵合金微观结构、形貌、成分、海水耐蚀性及力学性能的影响。以期通过新工艺设计及新成分的引入两种方法,获得力学性能和海水耐蚀性优异的高熵合金。主要研究结果如下:1.铸态CoCrFeNi高熵合金具有单一的FCC固溶体结构,微区形貌为典型的树枝晶结构。在力学性能方面,铸态CoCrFeNi高熵合金表现出优异的塑性变形能力;但屈服强度和显微硬度较低,分别为167 MPa和168.9 HV。对CoCrFeNi高熵合金进行不同形变量的预压处理发现,预压形变量为20%和50%的高熵合金依然保持着单一的FCC固溶体结构;而进行80%预压处理的合金其相结构发生了明显的改变,由单一的FCC固溶体转变为FeNi3型的金属间化合物相(FCC结构)。适当预压处理可以改善CoCrFeNi高熵合金的电化学海水耐蚀性,其中进行80%预压处理的合金点蚀电位右移,达到0.978 V,明显高于铸态CoCrFeNi高熵合金的0.157 V,并且出现了典型的二次钝化现象,显示出优异的耐点蚀性。此外,适当的预压处理可以提高铸态CoCrFeNi高熵合金的力学性能,进行20%和50%预压处理的合金屈服强度分别达到544 MPa和784 MPa,明显高于铸态CoCrFeNi高熵合金的163 MPa,分别提升233%和380%。2.W0.2和Mo0.2添加使CoCrFeNiW0.2/Mo0.2高熵合金仍保持单一的FCC固溶体结构,少量的W和Mo可以完全固溶到合金晶格中,未能引起相结构变化;随着W和Mo含量的进一步提升,CoCrFeNi W0.5/Mo0.5高熵合金均在原有FCC固溶体结构的基础上分别析出了富W和富Mo的金属间化合物相,新析出的金属间化合物相沿枝晶间分布。W和Mo元素的添加均能提高铸态CoCrFeNi高熵合金的电化学海水耐蚀性,其中CoCrFeNi W0.5/Mo0.2高熵合金出现了明显的二次钝化现象。此外,CoCrFeNiW0.5高熵合金显示出最为优异的耐点蚀性,其点蚀电位达到1.112 V,明显高于铸态CoCrFeNi的0.157 V;其钝化区间由1.155 V提升到2.291 V,提升为原来的将近2倍,钝化膜稳定性得到较大的提升。W和Mo元素的添加均能显著提高铸态CoCrFeNi高熵合金的显微硬度及屈服强度,W0.2和Mo0.2合金力学性能的增强与固溶强化有关,W0.5和Mo0.5合金的强化机制为固溶强化和第二相增强理论。其中,Mo0.5添加的高熵合金显微硬度达到356HV,屈服强度和极限抗压强度分别为604 MPa和1724 MPa,极限应变量达到49.1%,表现出优异的综合力学性能。
[Abstract]:High entropy alloy has broken the traditional concept of alloying ratio. It is usually prepared by equal or near equal atomic ratio. Because of its new design idea, unique structure, excellent mechanical properties, good corrosion resistance, high entropy alloy is a new type of alloy, because of its new design concept, unique structure, excellent mechanical properties, good corrosion resistance, and good corrosion resistance. Wear resistance and electromagnetic properties have attracted extensive research interest and have broad prospects. In this paper, CoCrFeNiNix CoCrFeNiWx and CoCrFeNi Moxtrox0. 2) high entropy alloys were prepared by arc melting. X-ray diffractometer, differential scanning calorimeter, field emission scanning electron microscope and electrochemical workstation were used. The effects of predeformation treatment and element addition on the microstructure, morphology, composition, corrosion resistance and mechanical properties of high entropy alloy containing CoCrFeNi were studied by means of microhardness tester and MTS universal tester. The high entropy alloy with excellent mechanical properties and corrosion resistance of seawater can be obtained by the new process design and the introduction of new composition. The main results are as follows: 1. The as-cast CoCrFeNi high entropy alloy has a single FCC solid solution structure and a typical dendritic structure. In terms of mechanical properties, as cast CoCrFeNi high entropy alloy shows excellent plastic deformation ability, but its yield strength and microhardness are lower, which are 167 MPa and 168.9 HV, respectively. By prepressing CoCrFeNi high entropy alloy with different shape variables, it was found that the high entropy alloy with 20% and 50% precompression deformation still maintained a single FCC solid solution structure, while the phase structure of 80% prepress alloy changed obviously. The FCC structure was transformed from a single FCC solid solution to a FeNi3 type intermetallic compound. The electrochemical corrosion resistance of CoCrFeNi high entropy alloy can be improved by proper preloading, in which the pitting potential of 80% prepress alloy shifts to the right, reaching 0.978 V, which is obviously higher than that of as cast CoCrFeNi high entropy alloy (0.157 V), and the typical secondary passivation occurs. Show excellent pitting resistance. In addition, the mechanical properties of as-cast CoCrFeNi high entropy alloy can be improved by proper preloading treatment. The yield strength of the alloy treated with 20% and 50% precompression was 544 MPa and 784 MPA, respectively, which was significantly higher than that of the as-cast CoCrFeNi high entropy alloy (163 MPA). The CoCrFeNiW0.2/Mo0.2 high entropy alloy remained a single FCC solid solution structure by 233% increase and 380%.2.W0.2 and Mo0.2 addition, respectively. A small amount of W and Mo can be completely dissolved into the lattice of the alloy, and the phase structure can not be changed. With the further increase of W and Mo contents, W and Mo rich intermetallic compound phases were precipitated on the basis of the original FCC solid solution structure of CoCrFeNi W0.5/Mo0.5 high entropy alloys, respectively. The electrochemical corrosion resistance of as-cast CoCrFeNi high entropy alloy can be improved by the addition of new precipitated intermetallics. W and Mo elements along the dendritic phase. Among them, the CoCrFeNi W0.5/Mo0.2 high entropy alloy has obvious secondary passivation phenomenon. In addition, CoCrFeNiW0.5 high entropy alloy shows the most excellent pitting corrosion resistance, its pitting potential is 1.112 V, which is obviously higher than 0.157 V of as-cast CoCrFeNi, and its passivation range is raised from 1.155 V to 2.291 V, which is nearly twice as high as the original one. The stability of passivation film is improved greatly. W and Mo elements can improve the microhardness and yield strength of as cast CoCrFeNi high entropy alloy. The mechanical properties of W 0.2 and Mo0.2 alloys are related to solution strengthening. The strength of W 0.5 and Mo0.5 alloys is related to solution strengthening. The mechanism is solid solution strengthening and second phase enhancement theory. The microhardness, yield strength and ultimate compressive strength of the high entropy alloy added with Mo0.5,604 MPa and 1724 MPA, respectively, and the ultimate strain reached 49.1%, showing excellent comprehensive mechanical properties.
【学位授予单位】：济南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139

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