金属玻璃力学行为的分子动力学模拟研究
发布时间：2018-08-09 20:07
【摘要】：金属玻璃又称非晶态合金,是材料家族中的新成员。金属玻璃由于其特殊的无序态金属键结构,同时具有玻璃、金属、固体和液体特性,表现出非常独特的性能。它不仅有望成为一种性能优异的新型金属材料,同时也是研究材料科学与凝聚态物理中一些重要基本问题的良好模型体系。金属玻璃的力学性能尤其受到了各界人士的关注,包括超高的强度,超大的弹性和超强的耐磨性等。然而,在金属玻璃实现工业化应用过程中,还有许多困难有待解决,同时,一些基本的科学问题也尚不清晰。如金属玻璃增韧的方法和有效性,剪切带的结构特性,金属玻璃的小尺寸效应,以及金属玻璃的微观变形单元与宏观变形之间的关联等。本文通过分子动力学模拟方法,系统研究了在金属玻璃,主要是CuZr体系中,通过结构调控的方法,观察到不同的力学变形行为,并解释各自的变形机理。得到的主要结果如下所示：(1)通过分子动力学方法,系统研究了Cu64Zr36以及Cu40Zr60两种成分中的拉伸变形行为与微观STZ的演化之间的关系。研究发现在应力达到最大值之后,样品中开始出现一些原子,它们具有较大的局域原子应变(或位移),可将其定义为S原子。在最大应力之后,S原子率先在“孔隙区”附近,以及一些类液形的Voronoi构型中产生。当进一步的变形时,一些非“孔隙区”区域,或构型为类固形的Voronoi构型中,也会产生S原子。此后,伴随着剪切带的开始萌生,S原子主要集中在剪切带上产生。可以将STZ的大小定义为S原子以及其周围最近邻原子的总数,相互连接的原子属于同一个STZ。计算发现平均STZ大小与应变的大小密切相关,在7%到12%应变范围内,该值从17±3变化到106±6。以上结果部分解释了为什么不同的实验测试方法会得出不一样的STZ的大小。接下来,我们进一步分析了随着应变的增加,STZ大小的分布的变化情况。研究发现,完整剪切带的形成与大尺寸STZ的产生密切相关。我们的研究结果有助于进一步推进构建宏观剪切带与微观STZ之间关联的研究。(2)通过分子动力学方法,在Cu64Zr36,Cu36Zr64,以及Ni40Zr60三种体系中研究了单根剪切带的力学变形行为,发现它在拉伸条件下应力应变曲线中没有出现“应力过冲”现象,并且经过20%变形后宏观样品形状未发生变化,表现出一种标准的均匀变形行为。并且,这种特殊的变形行为不受尺寸因素的制约,在更大尺寸的体系中也观察到了相同的现象,暗示着这个现象很可能扩展至宏观尺度上。同时,通过对剪切带在不同温度下退火,可以实现变形模式的连续转变。此外,通过快速冷却的方法,同样可以获得“类剪切带”的结构,实现均匀变形行为。并且,利用Voronoi多面体以及“孔隙区”分析方法系统研究了样品的结构随着不同退火温度以及冷却速率的变化。发现,“类剪切带”结构的样品中,其“孔隙区”以及“类液区”具有较大的相对原子含量,这使其更加倾向于发生均匀变形。以上结论在Cu64Zr36,Cu36Zr64,以及Ni40Zr60三种体系中都成立,并得到了实验上的验证。我们的研究结果对于在实验中大尺寸样品制备出具有宏观塑性性能的金属玻璃材料,提供了一些新的思路。(3)通过分子动力学方法,系统研究了Cu20Zr80,Cu40Zr60,Cu50Zr50,Cu64Zr36以及Cu80Zr20五个成分中不同厚度金属玻璃薄膜样品的拉伸力学行为。研究发现在Cu-Zr体系中的五个成分中,都发生了随着薄膜厚度的减小,其变形模式发生从局域化变形到非局域化变形的转变。研究证明了这种与尺寸相关的变形模式的变化,与变形过程中的应变能有关。当累积的应变能足够大,则材料发生局域化变形,而若累积的能量不足,则发生非局域化变形。同时,不同成分中,其临界尺寸会随着成分发生变化,并且被证明与形成单个S原子(或者说STZ)所需要的激活能量有关。激活能越高,临界尺寸越小。对CusoZrso不同厚度金属玻璃薄膜的研究,还发现,厚度越小,它的弹性模量越低,强度越低,密度越低,泊松比越低。这种性能上的差异,是由于具有低密度的表面层(约0.4纳米)的相对原子含量,在整体样品中所占据的比例不同所致。我们的研究结果有助于推进对尺寸导致的变形模式转变的进一步的研究。(4)通过分子动力学方法,系统研究了以Cu64Zr36(A), CusoZrso(B), Cu4oZr6o(C)三种单相材料为基础,构建出不同种类多层膜结构复合材料的拉伸力学行为。我们通过不同的组合模式,来对材料的强度进行调控,并以此实现对材料变形模式的调控。研究发现多层膜的层数是决定变形模式转变的重要因素,当层数超过或等于七层时,在A相与C相的组合,以及A相与B相的组合中,都能观察到非局域化变形模式的发生。进一步的分析发现,多层膜的变形模式与构成它的单元(即单层膜)的变形模式有所关联,但并不能由其决定。此外,多层膜的变形模式可以通过能量判据和不均匀程度分析来定性地解释。我们的研究结果有助于推进在纯非晶态结构中增强塑性的进一步的探索。
[Abstract]:Metallic glass, also known as amorphous alloy, is a new member of the family of materials. Metal glass, due to its special disorder metal bond structure, has the characteristics of glass, metal, solid and liquid, shows very unique properties. It is not only expected to be a new type of metal material with excellent performance, but also the research of material science and coagulation. A good model system for some important basic problems in state physics. The mechanical properties of metal glass are especially concerned by people from all walks of life, including ultra high strength, super elasticity and super strong wear resistance. However, there are still many difficulties to be solved in the process of industrial application of metal glass. At the same time, some basic scientific questions are needed. The method and effectiveness of toughening of metal glass, the structural characteristics of the shear band, the small size effect of the metallic glass, and the correlation between the microscopic deformation unit and the macroscopic deformation of the metal glass are also studied. This paper systematically studies the structure of metal glass, mainly in the CuZr system, through the molecular dynamics simulation method. The main results are as follows: (1) the relationship between the tensile deformation behavior of the Cu64Zr36 and the two components of the Cu40Zr60 and the evolution of the microcosmic STZ is systematically studied by molecular dynamics method. The study finds that the maximum stress is reached. After that, the samples begin to appear some atoms, which have larger local atomic strain (or displacement), which can be defined as S atoms. After the maximum stress, S atoms take the lead in the formation of the "pore zone", and some liquid like Voronoi configurations. When further deformation, some non "pore zone" regions, or the configuration of the type are solid. In the form of the Voronoi configuration, the S atom is also produced. Thereafter, with the beginning of the shear band, the S atom is mainly concentrated on the shear band. The size of the STZ can be defined as the S atom and the total number of adjacent adjacent atoms around it. The interconnected atoms belong to the same STZ. calculation and found that the average STZ size is closely related to the size of the strain. In the 7% to 12% strain range, the value of the value from 17 + 3 to 106 + 6. explains why different experimental methods will produce different sizes of STZ. Next, we further analyze the changes in the distribution of the STZ size as the strain increases. The study shows that the formation of the complete shear band and the large size STZ The results of our study are helpful to further promote the study of the association between macroscopic shear bands and microcosmic STZ. (2) the mechanical deformation of single shear bands in the Cu64Zr36, Cu36Zr64 and Ni40Zr60 systems is studied by molecular dynamics method, and it is found that it is in the stress-strain curve under the tensile condition. There is no "stress overshoot" phenomenon, and the shape of the macro sample has not changed after 20% deformation, showing a standard uniform deformation behavior. Moreover, this special deformation behavior is not restricted by the size factor, and the same phenomenon is observed in the larger size system, suggesting that this phenomenon is likely to expand to the extent. At the same time, the shear band can be transformed continuously by annealing at different temperatures. In addition, the structure of the "shear band" can be obtained by rapid cooling, and the Voronoi polyhedron and the pore zone analysis method are used to study the samples. With the change of the annealing temperature and cooling rate, it is found that in the samples of the "class shear band" structure, the "pore zone" and the "liquid like zone" have larger relative atomic content, which makes it more inclined to have uniform deformation. The above conclusion is established in the three systems of Cu64Zr36, Cu36Zr64, and Ni40Zr60. Experimental verification. Our results provide some new ideas for the preparation of metal glass materials with macro plastic properties in large size samples in the experiment. (3) through molecular dynamics, the metal glass films with different thickness of Cu20Zr80, Cu40Zr60, Cu50Zr50, Cu64Zr36 and Cu80Zr20 are systematically studied. The tensile mechanical behavior of the sample is found. It is found that in the five components of the Cu-Zr system, the deformation modes occur from localized deformation to non localized deformation with the decrease of the thickness of the film. The study shows that the change of the deformation mode related to the size dependent deformation process is related to the strain energy during the deformation process. When the energy is large enough, the material is localized and deformed, and the localized deformation occurs if the accumulated energy is insufficient. At the same time, the critical size varies with the composition in the different components, and is proved to be related to the activation energy required for the formation of a single S atom (or STZ). The higher the activation energy, the smaller the critical size. CusoZrso The study of metal glass films with different thickness also found that the smaller the thickness, the lower the modulus, the lower the strength, the lower the density and the lower the Poisson's ratio. The difference in performance is due to the relative atomic content of the low density surface layer (about 0.4 nanometers) and the different proportion in the whole body. Further research on the transformation of deformation patterns caused by size is further promoted. (4) through molecular dynamics, the tensile mechanical behavior of different kinds of multilayer composite materials is constructed based on Cu64Zr36 (A), CusoZrso (B), Cu4oZr6o (C), and the tensile mechanical behavior of the composite materials of different kinds of multilayer films is constructed. The strength of the material is regulated and adjusted to control the deformation mode of the material. It is found that the number of layers is an important factor determining the transformation of the deformation mode. When the number of layers exceeds or equal to seven layers, the combination of the A phase and the C phase and the combination of the A phase and the B phase can observe the occurrence of the non localized deformation mode. It is found that the deformation mode of the multilayer film is related to the deformation mode of its unit (the monolayer), but it can not be determined by it. In addition, the deformation mode of the multilayer film can be explained qualitatively by the energy criterion and the analysis of the inhomogeneity. Our research results help to promote the enhancement of the plasticity in the pure amorphous structure. A step of exploration.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8
，
本文编号：2175173
[Abstract]:Metallic glass, also known as amorphous alloy, is a new member of the family of materials. Metal glass, due to its special disorder metal bond structure, has the characteristics of glass, metal, solid and liquid, shows very unique properties. It is not only expected to be a new type of metal material with excellent performance, but also the research of material science and coagulation. A good model system for some important basic problems in state physics. The mechanical properties of metal glass are especially concerned by people from all walks of life, including ultra high strength, super elasticity and super strong wear resistance. However, there are still many difficulties to be solved in the process of industrial application of metal glass. At the same time, some basic scientific questions are needed. The method and effectiveness of toughening of metal glass, the structural characteristics of the shear band, the small size effect of the metallic glass, and the correlation between the microscopic deformation unit and the macroscopic deformation of the metal glass are also studied. This paper systematically studies the structure of metal glass, mainly in the CuZr system, through the molecular dynamics simulation method. The main results are as follows: (1) the relationship between the tensile deformation behavior of the Cu64Zr36 and the two components of the Cu40Zr60 and the evolution of the microcosmic STZ is systematically studied by molecular dynamics method. The study finds that the maximum stress is reached. After that, the samples begin to appear some atoms, which have larger local atomic strain (or displacement), which can be defined as S atoms. After the maximum stress, S atoms take the lead in the formation of the "pore zone", and some liquid like Voronoi configurations. When further deformation, some non "pore zone" regions, or the configuration of the type are solid. In the form of the Voronoi configuration, the S atom is also produced. Thereafter, with the beginning of the shear band, the S atom is mainly concentrated on the shear band. The size of the STZ can be defined as the S atom and the total number of adjacent adjacent atoms around it. The interconnected atoms belong to the same STZ. calculation and found that the average STZ size is closely related to the size of the strain. In the 7% to 12% strain range, the value of the value from 17 + 3 to 106 + 6. explains why different experimental methods will produce different sizes of STZ. Next, we further analyze the changes in the distribution of the STZ size as the strain increases. The study shows that the formation of the complete shear band and the large size STZ The results of our study are helpful to further promote the study of the association between macroscopic shear bands and microcosmic STZ. (2) the mechanical deformation of single shear bands in the Cu64Zr36, Cu36Zr64 and Ni40Zr60 systems is studied by molecular dynamics method, and it is found that it is in the stress-strain curve under the tensile condition. There is no "stress overshoot" phenomenon, and the shape of the macro sample has not changed after 20% deformation, showing a standard uniform deformation behavior. Moreover, this special deformation behavior is not restricted by the size factor, and the same phenomenon is observed in the larger size system, suggesting that this phenomenon is likely to expand to the extent. At the same time, the shear band can be transformed continuously by annealing at different temperatures. In addition, the structure of the "shear band" can be obtained by rapid cooling, and the Voronoi polyhedron and the pore zone analysis method are used to study the samples. With the change of the annealing temperature and cooling rate, it is found that in the samples of the "class shear band" structure, the "pore zone" and the "liquid like zone" have larger relative atomic content, which makes it more inclined to have uniform deformation. The above conclusion is established in the three systems of Cu64Zr36, Cu36Zr64, and Ni40Zr60. Experimental verification. Our results provide some new ideas for the preparation of metal glass materials with macro plastic properties in large size samples in the experiment. (3) through molecular dynamics, the metal glass films with different thickness of Cu20Zr80, Cu40Zr60, Cu50Zr50, Cu64Zr36 and Cu80Zr20 are systematically studied. The tensile mechanical behavior of the sample is found. It is found that in the five components of the Cu-Zr system, the deformation modes occur from localized deformation to non localized deformation with the decrease of the thickness of the film. The study shows that the change of the deformation mode related to the size dependent deformation process is related to the strain energy during the deformation process. When the energy is large enough, the material is localized and deformed, and the localized deformation occurs if the accumulated energy is insufficient. At the same time, the critical size varies with the composition in the different components, and is proved to be related to the activation energy required for the formation of a single S atom (or STZ). The higher the activation energy, the smaller the critical size. CusoZrso The study of metal glass films with different thickness also found that the smaller the thickness, the lower the modulus, the lower the strength, the lower the density and the lower the Poisson's ratio. The difference in performance is due to the relative atomic content of the low density surface layer (about 0.4 nanometers) and the different proportion in the whole body. Further research on the transformation of deformation patterns caused by size is further promoted. (4) through molecular dynamics, the tensile mechanical behavior of different kinds of multilayer composite materials is constructed based on Cu64Zr36 (A), CusoZrso (B), Cu4oZr6o (C), and the tensile mechanical behavior of the composite materials of different kinds of multilayer films is constructed. The strength of the material is regulated and adjusted to control the deformation mode of the material. It is found that the number of layers is an important factor determining the transformation of the deformation mode. When the number of layers exceeds or equal to seven layers, the combination of the A phase and the C phase and the combination of the A phase and the B phase can observe the occurrence of the non localized deformation mode. It is found that the deformation mode of the multilayer film is related to the deformation mode of its unit (the monolayer), but it can not be determined by it. In addition, the deformation mode of the multilayer film can be explained qualitatively by the energy criterion and the analysis of the inhomogeneity. Our research results help to promote the enhancement of the plasticity in the pure amorphous structure. A step of exploration.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8
，
本文编号：2175173
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