纳米多晶铝及其复合材料微观变形机理的研究
发布时间：2018-11-10 15:59
【摘要】：颗粒增强金属基复合材料具有优异的性能,应用领域非常广泛。但是在实际生产加工过程中还存在很多问题,例如复合材料的强度或延展性达不到要求等,这就需要对金属基复合材料的性能有进一步认识。当前通过分子动力学方法对纳米金属及其复合材料的研究已经受到越来越多的关注,在原子层面对纳米金属及其复合材料拉伸过程中的微观结构变化进行分析,可以更清楚的了解纳米金属及其复合材料的力学性能以及变形机制。本文应用分子动力学方法分别对金属多晶Al和β-SiC/Al复合材料进行拉伸行为的模拟,重点研究多晶Al和β-SiC/Al复合材料的力学性能和微观变形机制。通过Voronoi方法建立了不同晶粒尺寸的多晶Al块体模型,在此基础上对其进行拉伸模拟。弛豫后晶界处原子数比率会增加,并且随着晶粒尺寸的减小,晶界处原子含量增加。多晶Al块体截面的原子能量分布呈盆地状,晶界处原子能量比内部晶粒的要高。重点讨论了不同晶粒尺寸对多晶Al块体拉伸变形的影响,结合拉伸过程的能量变化情况分析了其变形机制。结果表明：随着晶粒尺寸的减小,多晶Al块体的屈服强度减小,遵循反Hall-Petch关系。晶粒尺寸较大的多晶Al块体拉伸过程有位错原子产生,形成交叉位错,位错扩展到晶界,被晶界阻碍运动,对材料起到强化作用,同时有晶界滑移和晶粒旋转的发生；晶粒尺寸较小的多晶Al块体拉伸过程主要是晶界处产生大量缺陷原子,裂纹会在大量缺陷原子处产生。此外,温度的增加、应变率的下降均使多晶Al块体的屈服强度下降。建立了体积含量相同、SiC颗粒尺寸不同的多种β-SiC/Al复合材料模型,并开展拉伸模拟。通过统计复合材料弛豫后晶界原子数比率得知,SiC颗粒尺寸越小,晶界原子数含量越多。重点讨论了该复合材料力学性质的增强效果,并结合拉伸过程的能量曲线变化分析了材料的变形机制。结果表明：随着SiC颗粒尺寸的减小,复合材料的屈服强度减小；β-SiC/Al复合材料的屈服强度和弹性模量与多晶Al比较均有所提高。β-SiC/Al复合材料在拉伸变形过程中,首先是基体Al在晶界处产生位错原子,并发生扩展；应变达到一定值,在基体Al上产生裂纹,裂纹靠近增强体SiC和基体Al之间的晶界处,而增强体SiC在拉伸过程不会遭到破坏。随着温度的增加、应变率的下降,β-SiC/Al复合材料的屈服强度均减小。
[Abstract]:Particle-reinforced metal matrix composites have excellent properties and are widely used in many fields. However, there are still many problems in the process of production and processing, such as the strength or ductility of the composites can not meet the requirements, which requires further understanding of the properties of metal matrix composites. At present, more and more attention has been paid to the study of nano-metal and its composites by molecular dynamics. The microstructure of nano-metal and its composites during tensile process is analyzed at atomic level. The mechanical properties and deformation mechanism of nano-metal and its composites can be clearly understood. In this paper, the tensile behavior of metal polycrystalline Al and 尾-SiC/Al composites were simulated by molecular dynamics method, and the mechanical properties and microscopic deformation mechanism of polycrystalline Al and 尾-SiC/Al composites were studied. The polycrystalline Al block model with different grain size was established by Voronoi method, and the tensile simulation was carried out on the basis of the model. The atomic number ratio at grain boundary increases after relaxation, and the atomic content increases with the decrease of grain size. The atomic energy distribution of the polycrystalline Al block section is basin like, and the atomic energy at the grain boundary is higher than that of the inner grain. The effect of different grain sizes on the tensile deformation of polycrystalline Al bulk is discussed, and the deformation mechanism is analyzed according to the energy variation of the tensile process. The results show that the yield strength of polycrystalline Al blocks decreases with the decrease of grain size and follows the inverse Hall-Petch relationship. The larger grain size polycrystalline Al bulk tensile process produced dislocation atoms, formed the cross dislocation, the dislocation extended to the grain boundary, was hindered by the grain boundary movement, played the strengthening role to the material, at the same time, the grain boundary slippage and the grain rotation occurred. The tensile process of polycrystalline Al bulk with small grain size is mainly caused by a large number of defect atoms at grain boundaries and cracks at a large number of defect atoms. In addition, the yield strength of polycrystalline Al blocks decreases with the increase of temperature and the decrease of strain rate. Several 尾-SiC/Al composite models with the same volume content and different SiC particle size were established and the tensile simulation was carried out. It is found that the smaller the size of SiC particles, the more the number of atoms in grain boundary of composite materials after relaxation. The reinforcing effect of the mechanical properties of the composite is discussed emphatically, and the deformation mechanism of the composite is analyzed in combination with the change of the energy curve of the tensile process. The results show that the yield strength of the composite decreases with the decrease of SiC particle size. The yield strength and elastic modulus of 尾-SiC/Al composites are higher than that of polycrystalline Al composites. During the tensile deformation of 尾-SiC/Al composites, dislocation atoms are first produced at grain boundaries by matrix Al and propagated. When the strain reaches a certain value, cracks occur on the matrix Al, and the crack is near the grain boundary between the SiC and the matrix Al, while the SiC of the reinforcements will not be destroyed during the tensile process. With the increase of temperature and the decrease of strain rate, the yield strength of 尾-SiC/Al composites decreases.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB33;O614.31
本文编号：2322893
[Abstract]:Particle-reinforced metal matrix composites have excellent properties and are widely used in many fields. However, there are still many problems in the process of production and processing, such as the strength or ductility of the composites can not meet the requirements, which requires further understanding of the properties of metal matrix composites. At present, more and more attention has been paid to the study of nano-metal and its composites by molecular dynamics. The microstructure of nano-metal and its composites during tensile process is analyzed at atomic level. The mechanical properties and deformation mechanism of nano-metal and its composites can be clearly understood. In this paper, the tensile behavior of metal polycrystalline Al and 尾-SiC/Al composites were simulated by molecular dynamics method, and the mechanical properties and microscopic deformation mechanism of polycrystalline Al and 尾-SiC/Al composites were studied. The polycrystalline Al block model with different grain size was established by Voronoi method, and the tensile simulation was carried out on the basis of the model. The atomic number ratio at grain boundary increases after relaxation, and the atomic content increases with the decrease of grain size. The atomic energy distribution of the polycrystalline Al block section is basin like, and the atomic energy at the grain boundary is higher than that of the inner grain. The effect of different grain sizes on the tensile deformation of polycrystalline Al bulk is discussed, and the deformation mechanism is analyzed according to the energy variation of the tensile process. The results show that the yield strength of polycrystalline Al blocks decreases with the decrease of grain size and follows the inverse Hall-Petch relationship. The larger grain size polycrystalline Al bulk tensile process produced dislocation atoms, formed the cross dislocation, the dislocation extended to the grain boundary, was hindered by the grain boundary movement, played the strengthening role to the material, at the same time, the grain boundary slippage and the grain rotation occurred. The tensile process of polycrystalline Al bulk with small grain size is mainly caused by a large number of defect atoms at grain boundaries and cracks at a large number of defect atoms. In addition, the yield strength of polycrystalline Al blocks decreases with the increase of temperature and the decrease of strain rate. Several 尾-SiC/Al composite models with the same volume content and different SiC particle size were established and the tensile simulation was carried out. It is found that the smaller the size of SiC particles, the more the number of atoms in grain boundary of composite materials after relaxation. The reinforcing effect of the mechanical properties of the composite is discussed emphatically, and the deformation mechanism of the composite is analyzed in combination with the change of the energy curve of the tensile process. The results show that the yield strength of the composite decreases with the decrease of SiC particle size. The yield strength and elastic modulus of 尾-SiC/Al composites are higher than that of polycrystalline Al composites. During the tensile deformation of 尾-SiC/Al composites, dislocation atoms are first produced at grain boundaries by matrix Al and propagated. When the strain reaches a certain value, cracks occur on the matrix Al, and the crack is near the grain boundary between the SiC and the matrix Al, while the SiC of the reinforcements will not be destroyed during the tensile process. With the increase of temperature and the decrease of strain rate, the yield strength of 尾-SiC/Al composites decreases.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB33;O614.31
【共引文献】
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1 谢根全,龙述尧;考虑小尺度效应影响的金属纳米丝弹性模量的计算[J];苏州科技学院学报(工程技术版);2005年02期
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