本文關鍵詞：AlFeCrCuX高熵合金力學性能的第一性原理計算　出處：《大連理工大學》2017年博士論文　論文類型：學位論文

  更多相關文章： 高熵合金 第一性原理 結構 彈性 塑性

【摘要】：高熵合金是上世紀九十年代發(fā)現(xiàn)并命名的一種新型合金,它突破了以一種或兩種元素為主元的傳統(tǒng)合金設計理念,近年來已成為材料研究的熱點之一。高熵合金被定義為五到十三種合金按照等原子比或接近于等原子比進行混合后所形成的合金,其中多主元金屬元素混合所產(chǎn)生的高熵效應,使高熵合金具有簡單的立方系晶體結構,并不形成金屬間化合物或復雜相,因此高熵合金表現(xiàn)出很多傳統(tǒng)合金所不具有的優(yōu)異性能,如高加工硬化性、高硬度、耐腐蝕性、耐高溫軟化性、高電阻率、耐高溫氧化性等。近幾年的研究又發(fā)現(xiàn)了一些較簡單的六方結構的高熵合金。但是目前對于高熵合金的研究大都靠實驗室支持,做一些高熵合金相組成、性能檢測和設計方面的工作,相關的理論研究較少,因此對其性能的研究結果非常有限。本文采用虛擬晶體近似的方法建立AlFeCrCuX(X=CoNi,TiZn)高熵合金的晶體模型,利用基于密度泛函理論的第一性原理的CASTEP軟件包,計算了兩種典型高熵合金AlFeTiCrZnCu和AlCoCrCuFeNi的結構及穩(wěn)定性、彈性和塑性性能。通過對AlFeCrCuX(X=CoNi,TiZn)高熵合金結構性能的計算發(fā)現(xiàn),高熵合金的原子種類較多的晶格常數(shù)小,密度大,說明多原子的高熵合金結合能較大,結構穩(wěn)定;高熵合金元素含量對其結構也有一定影響,Al、Ti、Cr等元素含量增加會使高熵合金的晶格常數(shù)增大,密度減小,Fe和Ni等元素含量增加會使高熵合金的晶格常數(shù)減小,密度增大。對AlFeCrCuX(X=CoNi,TiZn)高熵合金基態(tài)總能量和生成熱進行計算,生成熱決定了高熵合金的熱力學穩(wěn)定性。六元合金體系的基態(tài)總能量最小,系統(tǒng)穩(wěn)定性最好。從生成熱計算結果中可以看出,除五元合金AlFeTiCrZn外的生成熱皆為負值,說明兩種高熵合金在熱力學性能是穩(wěn)定的,元素含量及壓力變化并不會改變高熵合金的熱力學穩(wěn)定性。高熵合金需要很大的壓力才會發(fā)生結構相變,因此在高壓作用下的穩(wěn)定性較好。AlFeCrCuX(X=CoNi,TiZn)高熵合金彈性性能的計算包括彈性常數(shù)、楊氏模量、體積彈性模量及剪切模量。通過彈性常數(shù)的計算結果可以判定高熵合金的力學穩(wěn)定性及延展性;而通過VRH近似方法計算的楊氏模量、體積彈性模量和剪切模量,還能得到高熵合金的泊松比及剪切模量與體積彈性模量的比值,因此可以判定高熵合金的脆/韌性。面心立方結構高熵合金AlxCoCrCuFeNi的塑性主要是通過計算其廣義層錯能及廣義層錯能曲線來解釋位錯機制而體現(xiàn)。除了位錯機制中的非穩(wěn)定層錯能及本征層錯能的計算,二者的比值也對于解釋位錯機制至關重要。為了進一步描述位錯分布還引入了P—N模型,并計算了 AlxCoCrCuFeNi高熵合金的Peierls應力及屈服強度。
[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.
【學位授予單位】：大連理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG139

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