耐高温高熵合金的成分设计和性能优化

发布时间：2018-04-18 10:23

本文选题：耐高温高熵合金 + 模拟相图　；参考：《太原理工大学》2017年硕士论文

【摘要】：高熵合金是由至少四种主元形成的固溶体合金,其基本特征是混合熵高,合金相以简单固溶体为主,其综合性能优异,如硬度高、韧性好、良好的耐磨性和耐蚀性等。特别是在高温条件下,高熵合金的相结构稳定、强度高,有望成为新一代高温工程结构材料。本文结合计算机模拟相图(CALPHAD)、第一性原理密度泛函计算(DFT)和物化参数判据,设计了NbTaV-(Ti,Mo,W)耐高温高熵合金系,采用高真空电弧熔炼法成功制备出这五种合金,并研究了合金的铸态微观组织结构、力学性能和强化机制。主要研究结果如下:(1)制备的NbTaTiV、NbTaVW、NbTaTiVW、MoNbTaV和MoNbTaTiV五种耐高温高熵合金均为单相体心立方结构固溶体。在室温下,五种合金均呈现高强度大塑性,其中MoNbTaTiV综合性能优异,屈服强度1.4 GPa,断裂强度2.45 GPa,塑性达到30%;在温度为1273 K时,NbTaTiVW的硬度是镍基高温合金In 718和In 718 H的2.5倍。研究表明,钛元素的添加有利于提高合金塑性;钼、钨元素的添加有利于提高合金强度。(2)与建立在Miedema模型的物化参数判据相比,CALPHAD计算不仅可以模拟合金的平衡和非平衡相图,还能有效地描述固相和液相的热力学性质随温度的变化,并且预测在非平衡凝固过程中合金各组元的微观偏析。(3)NbTaV-(Ti,Mo,W)五种高熵合金的晶格常数均符合混合定律;通过DFT计算表明,每种合金的原子体积和弹性性质(体模量和剪切模量)也符合混合定律。(4)通过统计多种单相体心立方结构耐高温高熵合金在室温下的力学性能,发现合金硬度约为其屈服强度的三倍,合金的主要强化机制为固溶强化。建立了适用于铸态体心立方结构高熵合金的半经验模型,可以有效预测合金的屈服强度和硬度。
[Abstract]:High entropy alloy is a kind of solid solution alloy formed by at least four principal components. Its basic characteristics are high mixing entropy, simple solid solution and excellent comprehensive properties, such as high hardness, good toughness, good wear resistance and corrosion resistance, etc.Especially at high temperature, the phase structure of high entropy alloy is stable and its strength is high, which is expected to become a new generation of high temperature engineering structural materials.In this paper, the high-temperature and high-entropy alloy system of NbTaV-TiTi-Mo-W has been designed by using computer simulation phase diagram (CALPHADA), first-principle density functional calculation (DFTT) and physicochemical parameter criterion. The five alloys have been successfully prepared by high vacuum arc melting.The microstructure, mechanical properties and strengthening mechanism of the as-cast alloy were studied.The main results are as follows: NbTaTiVU NbTaVWN NbTaTiVWU MoNbTaV and MoNbTaTiV five high-temperature high-entropy alloys are single-phase body-centered cubic structure solid solutions.At room temperature, all the five alloys exhibit high strength and large plasticity, of which MoNbTaTiV has excellent comprehensive properties, yield strength is 1.4GPaand fracture strength is 2.45GPa.The hardness of NbTaTiVW is 2.5 times higher than that of Ni-base superalloys in 718 and in 718H at 1273 K.The results show that the addition of titanium can improve the plasticity of the alloy, the addition of molybdenum and tungsten can improve the strength of the alloy, and the calculation of physical and chemical parameters based on the Miedema model can not only simulate the equilibrium and non-equilibrium phase diagrams of the alloy, but also improve the strength of the alloy.The thermodynamic properties of solid and liquid phases can also be described effectively with the change of temperature, and the lattice constants of five kinds of high entropy alloys, I. e., the microsegregation of each component of the alloy during nonequilibrium solidification, are all in accordance with the mixing law, and the DFT calculation shows that the lattice constants of the five kinds of high entropy alloys are in accordance with the mixing law.The atomic volume and elastic properties (bulk modulus and shear modulus) of each alloy also conform to the law of mixing.It is found that the hardness of the alloy is about three times of its yield strength, and the main strengthening mechanism of the alloy is solution strengthening.A semi-empirical model for high entropy alloys with as-cast body centered cubic structure is established, which can effectively predict the yield strength and hardness of the alloys.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139

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