【作者】 邓太庆；

【导师】 胡连喜；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 TiAl基合金因其轻质、高温强度、抗蠕变和抗氧化性能突出等优点,引起了国内外学者的广泛关注。但这类材料的塑性差、高温变形抗力大,使其难以加工成形,阻碍了其实用化。为了更好地理解TiAl基合金在等温成形过程中的变形规律及其影响因素,避免大量人力、物力和财力的浪费,有限元技术在研究零件成形过程中发挥了重要作用,它为预测成形过程中的变形行为、可能产生的缺陷和确定最佳工艺参数等提供了理论依据。本文通过等温恒应变速率压缩实验和正交实验的研究,揭示了Ti-47Al(原子比)合金热变形过程中变形温度、应变速率和应变对流动应力的影响规律,发现Ti-47Al合金流动应力受变形温度和应变速率影响显著,是热敏感型和应变速率敏感型材料。以Ti-47Al合金高温变形的应力—应变曲线的特征分析为基础,利用逐步回归法建立了Ti-47Al合金的高温变形时的流动应力模型。该模型不仅考虑了变形温度、应变和应变速率对变形行为的影响,而且使用方便。验证结果表明,Ti-47Al合合金高温变形时的流动应力模型能较好地描述合金的高温变形行为,为提高数值模拟精度提供了一定条件。基于DEFORM/2D平台材料流动应力模型子程序的开发,将Ti-47Al合金高温变形时的流动应力模型耦合到有限元中,建立了有限元变形—传热耦合的模拟系统,并对Ti-47Al合金连接件的等温锻造过程进行了二维变形—传热耦合模拟。研究了变形工艺参数,包括变形温度、上模速度、摩擦及坯料形状对零件成形过程中应力、应变和温升的影响,计算了各种变形条件下的位移—载荷曲线。研究结果表明,上模速度和变形温度对零件成形和所需载荷有着显著的影响。上述研究为Ti-47Al合金零件的等温锻造工艺的优化设计及质量控制提供了理论和技术上的支持。更多还原

【Abstract】 TiAl based alloys are widely studied because their light weight and excellent elevated temperature properties such as high strength retention, resistance to creep and oxidation. However, their application is currently limited by the poor ductility and strong resistance to deformation at elevated temperature. To understand the deofrmation behavior and the effect of process parameters on deformation of the Ti-47Al alloy during high temperature forming and decrease wasting of time, man power and cost, It is well known that FE technology is a perfect method and has played important part in the study on the metal forming processes, which can provide scientific foundation for predicting whether defects occurring or not and determining the optimal process parameters.In this paper, Based on the hot compression experimental study at isothermal constant strainrate and the Orthogonal experiment, the influence of deformation temperature, strain rate and strain on flow stress has acquired in hot deformation process of Ti-47Al alloys(atomic ratio). It is found that deformation temperature and strain rate have an notable influence on the flow stress of Ti-47Al alloys, and they are materials sensitive to hot and strain rate. Based on the characteristics of the stress-strain curves of the Ti-47Al alloy during high temperature deformation, a flow stress model of Ti-47Al alloy during high temperature deformation has been established by the stepwise regression method.In the flow stress model, the effcet of these thermomechanical parameters on temperature, strain rate and strain has been taken in to account.Furthermore, the flow stress model is easy to be used. The comparison of the calculated results with the experimental of the test samples shows that present constitutive relationship has a good reliability and can offer the essential prerequisites for improvement of numerical simulation precision of metal forming processes.Based on the developed flow stress interface subroutine program in DEFORM/2D software, a coupled 2D-simulation of deformation with heat transfer has been carried out for the isothermal forging of Ti-47Al alloy. The effect of process parameters, including the deformation temperature, the Punch velocity, the friction and the materials shape on the stress, strain and temperature raise during isothermal forging has been studied and load-journey curves with different thermomechanical parameters has been calculated.The results show that punch velocity and deformation temperature have significant effect on the workpiece forming. This work provides the theory and technique foundation for implementing process optimized design and quality control scheme of Ti-47Al alloy isothermal forging process.更多还原