【作者】 陈学伟；

【导师】 张士宏；

【作者基本信息】 大连理工大学 ， 材料学， 2007， 硕士

【摘要】 TC11钛合金是一种重要的航空和宇航材料，属于两相组织α+β热强钛合金，其相变点约为998～1020℃，具有屈服强度高、疲劳强度大等特点，可在500℃以上长期使用，是航空航天发动机零部件的理想材料。但由于其在锻造过程中容易出现破裂、起皱等现象，这些问题严重阻碍了TC11钛合金的应用。而目前通用的试错型的经验方法，无法从根本上解决这些问题。因此，可以有效的对断裂缺陷进行预测将会大大提高TC11合金锻件的质量和生产效率，促进其发展和应用。本文在TC11合金的热变形行为研究的基础上，通过连续损伤力学伤理论推导出了可以预测材料断裂的损伤演化模型，同时通过微观分析得到了TC11微观组织及其结构参数对材料断裂的影响以及其断裂的微观机理。本文通过对TC11钛合金热模拟实验研究，得到了材料在高温变形条件下的真实应力应变曲线、探讨了变形工艺参数(如变形温度、应变速率等)对材料流动应力的影响并建立了材料的高温本构方程。在此基础上，基于连续损伤力学理论，并考虑变形温度与应变速率对高温变形损伤的作用，建立了材料高温变形条件下的损伤演化模型。通过高温单向拉伸实验确定了模型参数，并利用所建立的模型进行了TC11钛合金等温压缩变形断裂的预测，预测结果表明，该模型能够很好的预测TC11合金在低应变速率变形时的断裂行为。研究了材料的微观组织及其结构参数对材料断裂性能的影响及断裂机理。通过改变热处理条件得到了不同的微观组织结构，并分析了TC11钛合金微观组织随热处理条件的演化规律以及α片层厚度、α相百分含量等微观结构参数随热处理条件的变化规律。进而通过拉伸实验，得到了不同微观结构参数在不同变形工艺条件下的关系曲线，分析了力学性能、损伤演化速率随微观组织参数(α片层厚度、α相百分含量等)的变化规律。最后，通过金相显微观察、扫描电镜观察等微观分析的方法观察了TC11合金由于变形所产生的微观缺陷，研究了材料断裂的微观机理。研究发现，导致TC11钛合金断裂的根本原因是由于α+β两相变形不协调，导致孔洞在两相边界处产生，然后孔洞连接并沿着β晶粒边界扩展，最终导致材料的断裂。更多还原

【Abstract】 As an important aerospace material, TC11 alloy is aα+βdual phase titanium alloy with the phasetransfer temperature between 998 and 1020℃. Because of its excellent properties such as high strength andfatigue resistance, it becomes an ideal material to make parts of aerospace engine. However, the applicationof TC11 alloy was so limited now because of the easily occurred defects such as fracture and fold duringforging process and the problem cannot be solved completely only by the present try- and -error method.So possible effective prediction of fracture can improve the efficiency and quality of the forged TC11 alloyparts and then promote the development and application of TC11 alloy. In this work, a damage evolutionmodel based on continuum damage mechanics theory was proposed to be used for fracture prediction. Andthe effect of microstructure and the microstructure parameters on the fracture process was analyzed. Thenthe fracture mechanism of TC11 alloy was discussed.First the stress-strain curves were obtained by physical simulation experiments and the effects ofdeformation conditions (temperature. strain rate)on the deformation behaviors were discussed and then theconstitutive equation was established. On this basis, the damage evolution model at high temperature wasestablished based on the continuum damage mechanics theory considering the effects of deformationconditions (temperature、strain rate) on damage evolution. Then the parameters of the model weredetermined by hot tensile tests. Finally, the proposed model was used to predict the fracture behaviorsduring upset forging. The results indicated that the model can predict the fracture successfully.The effects of the microstructure and the microstructure parameters on the fracture process werediscussed and fracture mechanism of TC11 alloy was studied. First, different microstructures were obtainedby changing heat treatment conditions and the microstructure evolution was analyzed. Then the relationshipbetween the volume fraction and size ofαphase and the heat treatment conditions were built up. Therelationship between the microstructure parameters and the mechanical properties were also discussed asthe damage evolution rate was proposed. At last, the facture mechanism of TC11 alloy was investigatedbased on some micro telescope observation. It is found that incompatibility of deformation between theαandβphases could be the main cause of fracture. It begins with some cavities and then those cavitiescoalescence and growth and finally the fracture happen.更多还原