本文選題：TiAl合金　切入點(diǎn)：塑性變形　出處：《湘潭大學(xué)》2017年碩士論文

【摘要】：在航空航天、船舶及汽車等領(lǐng)域有廣闊應(yīng)用前景的輕質(zhì)金屬結(jié)構(gòu)材料中,TiAl基合金以其低密度、高比強(qiáng)度、良好的阻燃能力、抗氧化性及抗蠕變性能等倍受青睞。片層組織是TiAl基合金的典型微觀組織結(jié)構(gòu)之一,而片層組織中存在著的復(fù)雜取向與界面對其塑性行為有顯著影響。晶體塑性有限元方法結(jié)合晶體塑性變形理論與有限元方法,通過位錯(cuò)滑移與晶格畸變來描述材料的變形行為更加接近材料的塑性變形本質(zhì)。本研究基于晶體塑性理論,綜合考慮TiAl基合金的變形特征,建立單晶、雙晶及多晶片層結(jié)構(gòu)的有限元模型。借助ABAQUS/UMAT二次開發(fā)平臺,嵌入TiAl基合金塑性變形的本構(gòu)關(guān)系算法,模擬其拉伸變形,研究晶粒取向以及界面(晶界、相界)對TiAl基合金塑性行為的細(xì)觀影響機(jī)制。主要研究內(nèi)容如下:單晶拉伸變形中,晶粒以心部為中心發(fā)生顯著的轉(zhuǎn)動。平行于[1(?)0]普通滑移取向的晶粒拉伸時(shí)變形阻力最小,在變形中基本不發(fā)生轉(zhuǎn)動。而[(?)01]超滑移取向、[11(?)]孿生取向、[(?)01]任意取向的晶粒沿拉伸軸方向上的滑移阻力較大,引起其它方向上的滑移系搶先啟動,迫使晶粒須以扭轉(zhuǎn)來調(diào)整取向因子進(jìn)而協(xié)調(diào)變形。雙晶模型中,界面的存在導(dǎo)致晶體塑性變形不均勻,且在界面處形成應(yīng)力集中,相界的影響比晶界更顯著。同時(shí),含晶界和相界的雙晶中軟取向的滑移系啟動較為優(yōu)先,且為塑性應(yīng)變的主要貢獻(xiàn)者。晶界取向差角度對變形行為的影響表現(xiàn)為:小角度晶界處的應(yīng)力集中不明顯,體現(xiàn)較好的協(xié)調(diào)性。而大角度晶界處應(yīng)力集中突出,出現(xiàn)變形不協(xié)調(diào)現(xiàn)象。而且,在應(yīng)力集中區(qū)域出現(xiàn)二次硬化,容易萌生裂紋。多晶片層結(jié)構(gòu)的拉伸變形中,由于相鄰晶粒間界面的相互作用,晶粒間的變形有較好協(xié)調(diào)性。其變形機(jī)制為多滑移系的共同啟動,且滑移系的剪切變形不受軟硬剪切模式的影響。片層界面處應(yīng)力集中漸變分布,尤以三叉界面處的應(yīng)力最大。當(dāng)三叉界面由α_2相和γ相組成時(shí),應(yīng)力集中主要分布在靠近三叉界面的α_2相晶粒內(nèi);而由純γ相組成的三叉晶界,在靠近三叉晶界面的3個(gè)晶粒內(nèi)均有應(yīng)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 偽 -2 phase and 緯 phase, the stress concentration is mainly distributed in the 偽 2 phase grain near the triangulation interface, while the stress concentration exists in all the three grains near the trigeminal interface composed of pure 緯 phase.
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.23

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