镍基单晶高温合金静态再结晶实验研究及数值模拟

发布时间：2018-12-15 02:26

【摘要】：单晶高温合金涡轮叶片是现代先进航空发动机的关键热端部件,而再结晶缺陷显著地降低了其力学性能,需要极力避免。利用模拟技术和实验表征手段来研究单晶高温合金的再结晶机理,并探究单晶叶片的再结晶产生规律,对减少再结晶缺陷的出现、提高单晶叶片的成品率有着重要意义。考虑镍基单晶高温合金力学性能各向异性的特点,建立了可工程应用的热弹塑性模型,并利用回归方法分析获得DD6合金的关键本构参数。对典型几何特征进行了模拟分析,研究表明铸件几何结构对塑性变形的影响比晶体取向大很多,并预测了简单空心试棒易出现再结晶位置,预测结果与实验结果吻合良好。通过热压缩实验和压痕实验系统研究了单晶高温合金再结晶形核及长大机理。小变形条件下变形温度对再结晶敏感性有着重要影响,铸态非均匀组织影响再结晶微观组织演变。大塑性变形可以同时促进再结晶形核和提高再结晶晶界推移速度,而回复处理很难降低变形样品的再结晶倾向。变形组织中的层错缺陷可以促进再结晶形核,而共格γ′粒子会严重阻碍再结晶晶界的推移。此外,单晶材料的各向异性特点会影响再结晶区域的分布。建立了模拟单晶高温合金再结晶微观组织演变的元胞自动机(CA)模型。模型考虑了铸态枝晶组织及变形温度的影响,采用热弹塑性模型模拟得到再结晶驱动力分布,并获得了再结晶晶界推移激活能数据及其他相关模型参数。模拟了再结晶组织随时间的演变,并对比了等温及标准固溶条件下再结晶微观组织模拟与实验结果,两者吻合良好。讨论了再结晶动力学特点,并分析了非规则再结晶晶界的成因。考虑实际单晶空心涡轮叶片的结构特征,设计了两种简单铸件模型,开展了定向凝固实验及标准热处理实验。通过模拟分析塑形变形分布预测了再结晶易产生位置,并与实验结果进行了对比验证,两者吻合良好。铸造工艺引入的细小结构(如芯撑引起的凸起)容易产生再结晶。孔洞、凹槽、薄壁等应力集中特征不一定引起再结晶的产生,但多种特征影响的叠加易导致再结晶的出现。针对某实际单晶空心涡轮叶片,开展了定向凝固过程的温度场模拟和塑性变形模拟,分析和预测了其易于产生再结晶的位置,与实际生产结果大体吻合。最后,提出了减少单晶叶片定向凝固过程再结晶的工艺措施建议。
[Abstract]:Single crystal superalloy turbine blade is a key hot end component of modern advanced aero-engine. Recrystallization defects have significantly reduced its mechanical properties and need to be avoided. The recrystallization mechanism of single crystal superalloy and the regularity of recrystallization of single crystal blade are studied by means of simulation technology and experimental characterization. It is of great significance to reduce the appearance of recrystallization defects and improve the yield of single crystal blade. Considering the anisotropy of mechanical properties of Ni-based single crystal superalloys, a thermoelastic-plastic model for engineering applications was established, and the key constitutive parameters of DD6 alloys were obtained by regression analysis. The typical geometric characteristics are simulated and analyzed. The results show that the effect of geometric structure of castings on plastic deformation is much greater than that of crystal orientation, and the recrystallization position of simple hollow test bars is predicted. The predicted results are in good agreement with the experimental results. The mechanism of recrystallization nucleation and growth of single crystal superalloy was studied by thermal compression test and indentation test. Deformation temperature has an important effect on recrystallization sensitivity under small deformation condition, and the microstructure evolution of recrystallization is affected by non-uniform microstructure. Large plastic deformation can promote recrystallization nucleation and increase the rate of recrystallization grain boundary at the same time, but recovery treatment is difficult to reduce the recrystallization tendency of deformed samples. Laminated fault defects in deformed microstructure can promote recrystallization nucleation, while coherent 纬 'particles seriously hinder the recrystallization grain boundary. In addition, the anisotropy of single crystal material will influence the distribution of recrystallization region. A cellular automaton (CA) model was established to simulate the microstructure evolution of recrystallization of single crystal superalloys. The influence of as-cast dendritic structure and deformation temperature was taken into account in the model. The distribution of recrystallization driving force was simulated by thermoelastic-plastic model, and the activation energy data of recrystallization grain boundary and other related model parameters were obtained. The evolution of recrystallization microstructure with time was simulated, and the simulation results of recrystallization microstructure under isothermal and standard solution conditions were compared with the experimental results. The characteristics of recrystallization kinetics were discussed and the causes of irregular recrystallization grain boundaries were analyzed. Considering the structural characteristics of single crystal hollow turbine blades, two simple casting models were designed, and directional solidification experiments and standard heat treatment experiments were carried out. The location of recrystallization is predicted by simulation analysis of plastic deformation distribution, and the results are compared with the experimental results. The results are in good agreement with each other. The fine structure introduced by casting process, such as bulge caused by core brace, is easy to be recrystallized. The stress concentration characteristics of holes, grooves and thin-walled walls do not necessarily lead to recrystallization, but the superposition of various characteristics may lead to the occurrence of recrystallization. The simulation of temperature field and plastic deformation of a single crystal hollow turbine blade during directional solidification is carried out. The location of recrystallization is analyzed and forecasted, which is in good agreement with the actual production results. Finally, some technical measures to reduce the recrystallization of single crystal blade during directional solidification are put forward.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：V252;TG132.3

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