层片TiAl合金的微结构对力学行为的影响

IMECH-IR > 力学所知识产出(1956-2008)

	层片TiAl合金的微结构对力学行为的影响
	傅敏
导师	洪友士
	2000
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位类别	博士
学位专业	固体力学
关键词	Tial基合金疲劳行为裂纹萌生与扩展层间变形 Tial Alloy Fatigue Behaviour Crack Initiation And Propagation Interlamellar Deformation
英文摘要	本论文针对可能应用于叶片零部件的铸造全层片TiAl基合金进行了多方面的实验研究。目的着重于观测该材料的力学性能对微结构因素的敏感性及其失效行为，并以裂纹萌生为线索探讨其相关的物理和力学内禀机制的表征。研究工作涉及到多种跨越毫米尺度的宏－细－微观力学测试方法和技术，其中，新型试样的应力分析和可行性说明针对于脆怀板材试样并具有良好自对中能力的夹具设计是成功的。单调拉伸实验和拉一拉疲劳实验得到了所研究试样的基本力学性能和影响疲劳性能的微结构敏感因素，如晶粒取向、晶粒大小等。实验研究重点说明了层片取几因素对疲劳抗力的影响一与拉伸轴方向平行的晶粒具有最好的裂纹萌生抗力。扫描电镜和透射电镜下的原位拉伸实验得到了沿层片裂纹萌生的等征，这些等征包括：层片裂纹与拉伸轴夹角呈40°／60°／90°的方向倾向性、裂纹沿γ相真孪晶层片界面萌生的位置倾向性等。纳米压痕实验和原子力显微实验证了层片的弹性模量差异，为宏一细一微观分析提供了依据。分析和讨论工作针对于沿层片萌裂纹的方向的选择性和位置的倾向性等实验现象，以宏观界面力学方法和晶体学理论，侧重表征了与层间变形特性相关的力学和物理机制：（１）以模理量失配理论为基础提出了等效失配概念，得到瞪层片TiAl合金的等效失配度为0.16；（2）以界面能量释放率断裂准则为基础，提出了模式因子（TiAl,0.24）方法来评价拉、剪力的耦合作用；（3）根据以汤普森四面体所构筑的γ层间组合模型，并采用γ层片的惯习面间异类原子对数（NAT值）、穿层几何协调因子和穿层几何协调加和因子等方法分别表征其原子结构尺度下的界面结全强度和层间变形的位错协调性。分析和讨论重阐明了全层片TiAl有序合金的层间抗剪切能力较弱和γ层间真孪晶界面易于裂纹萌生等结果。; With respect to the future application of blade in aeroengine, specimens of an as-cast TiAl alloy with full lamellar structure were investigated under various types of tests, and the experimental results and related discussion are described in this paper. The study aims to discern the effect of microstructure factors in application reliability and failure behaviour, and to analyze intrinsic mechanisms regarding crack initiation. By adopting some experimental techniques, relevant results were obtained: In relation to a novel holder, related stress calculation and experiments prove its feasibility for brittle plate-shape specimens under tensile test owing to new gripping way and auto-alignment. The experiments of monotonic tension and cyclic loading aimed to study some factors on tensile and fatigue behaviour, the result is the key role of the orientation of lamellar interfaces. For instance, colonies with lamellar interface parallized to loading axis have the best resistance to fatigue failure. In situ tensile tests with scanning electronic microscopy and transmission electronic microscopy show some characters of interlamellar-crack initiation, e.g. inclinations of orientation, i.e. 40°/60°/90°, and site preference, i.e. γ interface of true twins. Experiments with nano-indenter and atomic force microscopy show the difference of elastic modulus of different lamellae, which provides the basis for related analyses. Based on the experimental phenomena of inclination of orientation and site of initiated cracks, along with the knowledge of crystallology and macro mechanics for interfaces of variants, the analyses characterize some related mechanical and physical mechanisms concerning interlamellar deformation. Thereby, some new concepts and solutions are proposed in this paper: (1) based on the theory of mismatch in elastic modulus, effective-mismatch index (TiAlε=0.16) is proposed; (2) in tems of the failure criterion in ratio of energy releasing, mode coefficient (TiAl, Z=0.24) is given to evaluate the synergic impact between tensile and shear stress; (3) resembling models for adjacent γ lamellae are established in Thompson tetrahedron, and new solutions of NAT (number of Al-Ti between habit planes of γ interlamellae), translamella-geometry-compatibility factor and its add-up factor are brought forward according to the models, so that the solutions can respectively characterize the binding strength and interlamellar deformation. The relevant discussion accentuates that, for full lamellar TiAl alloy, the shearing deformation along lamellar interfaces is dangerous for crack initiation, and, the true-twin interface of γ variants is prone to crack initiation.
索取号	29961
语种	中文
文献类型	学位论文
条目标识符	http://dspace.imech.ac.cn/handle/311007/23024
专题	力学所知识产出(1956-2008)
推荐引用方式 GB/T 7714	傅敏. 层片TiAl合金的微结构对力学行为的影响[D]. 北京. 中国科学院研究生院,2000.

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