AlFeCrCuX高熵合金力学性能的第一性原理计算

发布时间：2018-01-04 02:20

本文关键词：AlFeCrCuX高熵合金力学性能的第一性原理计算　出处：《大连理工大学》2017年博士论文　论文类型：学位论文

【摘要】：高熵合金是上世纪九十年代发现并命名的一种新型合金,它突破了以一种或两种元素为主元的传统合金设计理念,近年来已成为材料研究的热点之一。高熵合金被定义为五到十三种合金按照等原子比或接近于等原子比进行混合后所形成的合金,其中多主元金属元素混合所产生的高熵效应,使高熵合金具有简单的立方系晶体结构,并不形成金属间化合物或复杂相,因此高熵合金表现出很多传统合金所不具有的优异性能,如高加工硬化性、高硬度、耐腐蚀性、耐高温软化性、高电阻率、耐高温氧化性等。近几年的研究又发现了一些较简单的六方结构的高熵合金。但是目前对于高熵合金的研究大都靠实验室支持,做一些高熵合金相组成、性能检测和设计方面的工作,相关的理论研究较少,因此对其性能的研究结果非常有限。本文采用虚拟晶体近似的方法建立AlFeCrCuX(X=CoNi,TiZn)高熵合金的晶体模型,利用基于密度泛函理论的第一性原理的CASTEP软件包,计算了两种典型高熵合金AlFeTiCrZnCu和AlCoCrCuFeNi的结构及稳定性、弹性和塑性性能。通过对AlFeCrCuX(X=CoNi,TiZn)高熵合金结构性能的计算发现,高熵合金的原子种类较多的晶格常数小,密度大,说明多原子的高熵合金结合能较大,结构稳定;高熵合金元素含量对其结构也有一定影响,Al、Ti、Cr等元素含量增加会使高熵合金的晶格常数增大,密度减小,Fe和Ni等元素含量增加会使高熵合金的晶格常数减小,密度增大。对AlFeCrCuX(X=CoNi,TiZn)高熵合金基态总能量和生成热进行计算,生成热决定了高熵合金的热力学稳定性。六元合金体系的基态总能量最小,系统稳定性最好。从生成热计算结果中可以看出,除五元合金AlFeTiCrZn外的生成热皆为负值,说明两种高熵合金在热力学性能是稳定的,元素含量及压力变化并不会改变高熵合金的热力学稳定性。高熵合金需要很大的压力才会发生结构相变,因此在高压作用下的稳定性较好。AlFeCrCuX(X=CoNi,TiZn)高熵合金弹性性能的计算包括弹性常数、杨氏模量、体积弹性模量及剪切模量。通过弹性常数的计算结果可以判定高熵合金的力学稳定性及延展性;而通过VRH近似方法计算的杨氏模量、体积弹性模量和剪切模量,还能得到高熵合金的泊松比及剪切模量与体积弹性模量的比值,因此可以判定高熵合金的脆/韧性。面心立方结构高熵合金AlxCoCrCuFeNi的塑性主要是通过计算其广义层错能及广义层错能曲线来解释位错机制而体现。除了位错机制中的非稳定层错能及本征层错能的计算,二者的比值也对于解释位错机制至关重要。为了进一步描述位错分布还引入了P—N模型,并计算了 AlxCoCrCuFeNi高熵合金的Peierls应力及屈服强度。
[Abstract]:High entropy alloy is a new kind of alloy discovered and named in -10s. It breaks through the traditional design idea of one or two elements. In recent years, high entropy alloys have been defined as five to 13 alloys mixed with or close to equal atomic ratio. The high entropy effect caused by the mixing of multi-principal metal elements makes the high-entropy alloy have simple cubic crystal structure and do not form intermetallic compounds or complex phases. Therefore, high entropy alloys show many excellent properties, such as high work hardening, high hardness, corrosion resistance, high temperature softening resistance and high resistivity. In recent years, some simple high-entropy alloys with hexagonal structure have been found. However, most of the research on high-entropy alloys depends on the laboratory support, making some high-entropy alloy phase composition. There are few theoretical studies on performance testing and design. Therefore, the research results of its properties are very limited. In this paper, the crystal model of AlFeCrCuXX XCoNiNiTiZn) high entropy alloy is established by using the method of virtual crystal approximation. The first principle CASTEP software package based on density functional theory is used. The structure and stability of two typical high-entropy alloys, AlFeTiCrZnCu and AlCoCrCuFeNi, were calculated. Elastic and plastic properties. The calculation of the structure and properties of AlFeCrCuXX XCoNiZN) high entropy alloy shows that the lattice constant of the high entropy alloy with more kinds of atoms is small and the density is high. The results show that the high entropy alloy of polyatom has high binding energy and stable structure. The element content of high entropy alloy also has some influence on its structure. The increase of the content of elements such as Altin TiCr will increase the lattice constant and decrease the density of high entropy alloy. The increase of Fe and Ni content will decrease the lattice constant and increase the density of high entropy alloy. The total energy of ground state and heat of formation of TiZn-based high entropy alloy are calculated. The heat of formation determines the thermodynamic stability of high entropy alloy, and the total energy of ground state of six-element alloy system is the smallest. The stability of the system is the best. It can be seen from the calculation results of heat of formation that the heat of formation is negative except for five-element alloy AlFeTiCrZn, which indicates that the thermodynamic properties of the two kinds of high-entropy alloys are stable. The change of element content and pressure will not change the thermodynamic stability of high entropy alloy. Therefore, the stability of the alloy under high pressure is better. The calculation of the elastic properties of the high entropy alloy includes elastic constant and Young's modulus. The mechanical stability and ductility of high entropy alloy can be determined by the calculation results of elastic constants. The Poisson's ratio and the ratio of shear modulus to bulk elastic modulus of high entropy alloy can also be obtained from the Young's modulus, volume elastic modulus and shear modulus calculated by VRH approximation. Therefore, the brittleness / toughness of high entropy alloy can be determined. The plasticity of high entropy alloy AlxCoCrCuFeNi with face-centered cubic structure is mainly explained by calculating its generalized stacking fault energy and generalized stacking fault energy curve to explain the dislocation mechanism. Except for the calculation of unstable fault energy and intrinsic fault energy in dislocation mechanism. The ratio of the two is also very important to explain the dislocation mechanism. In order to further describe the dislocation distribution, the P-N model is also introduced. The Peierls stress and yield strength of AlxCoCrCuFeNi high entropy alloy were calculated.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139

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