取向与界面影响单晶及双相片层TiAl合金塑性行为的CPFEM模拟

发布时间：2018-04-07 19:10

本文选题：TiAl合金　切入点：塑性变形　出处：《湘潭大学》2017年硕士论文

【摘要】：在航空航天、船舶及汽车等领域有广阔应用前景的轻质金属结构材料中,TiAl基合金以其低密度、高比强度、良好的阻燃能力、抗氧化性及抗蠕变性能等倍受青睐。片层组织是TiAl基合金的典型微观组织结构之一,而片层组织中存在着的复杂取向与界面对其塑性行为有显著影响。晶体塑性有限元方法结合晶体塑性变形理论与有限元方法,通过位错滑移与晶格畸变来描述材料的变形行为更加接近材料的塑性变形本质。本研究基于晶体塑性理论,综合考虑TiAl基合金的变形特征,建立单晶、双晶及多晶片层结构的有限元模型。借助ABAQUS/UMAT二次开发平台,嵌入TiAl基合金塑性变形的本构关系算法,模拟其拉伸变形,研究晶粒取向以及界面(晶界、相界)对TiAl基合金塑性行为的细观影响机制。主要研究内容如下:单晶拉伸变形中,晶粒以心部为中心发生显著的转动。平行于[1(?)0]普通滑移取向的晶粒拉伸时变形阻力最小,在变形中基本不发生转动。而[(?)01]超滑移取向、[11(?)]孪生取向、[(?)01]任意取向的晶粒沿拉伸轴方向上的滑移阻力较大,引起其它方向上的滑移系抢先启动,迫使晶粒须以扭转来调整取向因子进而协调变形。双晶模型中,界面的存在导致晶体塑性变形不均匀,且在界面处形成应力集中,相界的影响比晶界更显著。同时,含晶界和相界的双晶中软取向的滑移系启动较为优先,且为塑性应变的主要贡献者。晶界取向差角度对变形行为的影响表现为:小角度晶界处的应力集中不明显,体现较好的协调性。而大角度晶界处应力集中突出,出现变形不协调现象。而且,在应力集中区域出现二次硬化,容易萌生裂纹。多晶片层结构的拉伸变形中,由于相邻晶粒间界面的相互作用,晶粒间的变形有较好协调性。其变形机制为多滑移系的共同启动,且滑移系的剪切变形不受软硬剪切模式的影响。片层界面处应力集中渐变分布,尤以三叉界面处的应力最大。当三叉界面由α_2相和γ相组成时,应力集中主要分布在靠近三叉界面的α_2相晶粒内;而由纯γ相组成的三叉晶界,在靠近三叉晶界面的3个晶粒内均有应力集中存在。
[Abstract]:TiAl-based alloys, which have broad application prospects in aerospace, ship and automobile, have been widely used in light metal structures for their low density, high specific strength, good flame retardancy, oxidation resistance and creep resistance.Lamellar structure is one of the typical microstructure of TiAl based alloy, and the complex orientation and interface in lamellar structure have significant influence on the plastic behavior of the lamellar alloy.Combined with the theory of crystal plastic deformation and the finite element method, the deformation behavior of the material is described by dislocation slip and lattice distortion, which is closer to the nature of plastic deformation of the material.Based on the theory of crystal plasticity and considering the deformation characteristics of TiAl based alloys, a finite element model of single crystal, double crystal and polycrystalline layers is established.Based on the ABAQUS/UMAT secondary development platform, the constitutive relation algorithm of plastic deformation of TiAl based alloy was embedded, and the tensile deformation was simulated. The influence mechanism of grain orientation and interface (grain boundary, phase boundary) on plastic behavior of TiAl base alloy was studied.The main research contents are as follows: during the tensile deformation of single crystal, the center of the grain rotates remarkably.The deformation resistance of grains parallel to the general slip orientation of [1] is the smallest, and it does not rotate during deformation.Superslip orientation, [11]In the twinning orientation, the grain with arbitrary orientation has higher slip resistance along the tensile axis, which causes the slip system in other directions to start first, forcing the grain to adjust the orientation factor by torsion and to coordinate the deformation.In the double crystal model, the existence of interface leads to the inhomogeneous plastic deformation of crystal, and the stress concentration is formed at the interface. The effect of phase boundary is more obvious than that of grain boundary.At the same time, the starting of soft orientation slip system in double crystal with grain boundary and phase boundary is preferred, and it is the main contributor of plastic strain.The effect of the angle of grain boundary orientation difference on the deformation behavior is as follows: the stress concentration at the small angle grain boundary is not obvious, which reflects better coordination.The stress concentration at the large angle grain boundary is prominent and the deformation is out of harmony.Furthermore, secondary hardening occurs in the stress concentration region and cracks are easily initiated.In the tensile deformation of polycrystalline lamellar structure, the deformation between grains is well coordinated due to the interaction between adjacent grain interfaces.The deformation mechanism is the joint initiation of multiple slip systems, and the shear deformation of the slip systems is not affected by the soft and hard shear modes.The stress concentration is gradually distributed at the lamellar interface, especially at the trigeminal interface.When the interface is composed of 伪 -2 phase and 纬 phase, the stress concentration is mainly distributed in the 伪 2 phase grain near the triangulation interface, while the stress concentration exists in all the three grains near the trigeminal interface composed of pure 纬 phase.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23

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