镍基单晶高温合金塑性流动中反常应力峰的波动行为研究

Nickel-base single crystal superalloy is the main material to manufacture turbine blades of advanced aeroengine. As temperature increases, the material’s flow stress increases anomalously to a peak value over a temperature range, and then decreases and loses load supporting capability. The resultant anomalous stress peak is the key to the mechanical properties of Nickel-base single crystal superalloy at high temperatures. For the fluctuation law and micro-mechanism of anomalous stress peak varying with temperature and strain rate over a wide range of temperatures and strain rates, it currently needs to be studied further. For this purpose, tests are conducted to measure the plastic flow behavior of Nickel-base single crystal superalloys at different temperatures （room temperature-1200 ℃） and strain rates （0.001-5000 /s）in this project. The fluctuation law varying with temperature and strain rate are analyzed. The micro-mechanism is revealed. In full consideration of the microstructure of Nickel-base single crystal superalloy, dislocation dynamics theory, fluctuation law of anomalous stress peak varying with temperature and strain rate as well as its micro-mechanism, a thermal viscoplastic constitutive relation is developed. The developed constitutive relation is able to describe the fluctuation behavior of the anomalous stress peak in the plastic flow of Nickel-base single crystal superalloys. This project can provide theoretical basis for engineering application of Nickel-base single crystal superalloy and reliability design of turbine blades in aeroengine.

镍基单晶高温合金是制造先进航空发动机涡轮叶片的关键材料。随着温度的升高，其流动应力在某一温度区域内反常增加并达到峰值，随后下降而失去承载能力，形成的反常应力峰是影响镍基单晶高温合金高温力学性能的关键。目前，国内外对于反常应力峰在很宽温度和应变率范围内随温度和应变率的波动规律及其机理的研究还有待进一步展开。为此，本项目拟对镍基单晶高温合金在不同温度（室温-1200℃）和应变率（0.001-5000/s）下的塑性流动行为进行测试，分析其中出现的反常应力峰随温度和应变率的波动规律，并揭示其微观机制。基于镍基单晶高温合金特有的微观结构及位错动力学理论，结合反常应力峰随温度和应变率的波动规律及其微观机制，建立可以描述镍基单晶高温合金塑性流动行为中反常应力峰波动行为的热粘塑性本构关系。本项目的开展为镍基单晶高温合金的工程应用以及航空发动机涡轮叶片的可靠性设计提供理论依据。

镍基高温合金是制造先进航空发动机热端部件的关键材料，其流动应力随温度变化会出现会反常应力峰，反常应力峰的出现使得传统的对金属塑性流动行为的认识、位错的热激活理论以及常见的金属热黏塑性本构关系均需要进一步完善。为此，本项目首先建立了一种超高温动态压缩试验的有效测试方法，利用该试验方法可实现1000℃以上各类材料的动态压缩性能测试。利用该试验方法并结合电子万能试验机，对两种镍基高温合金在宽温域宽应变率范围内的塑性流动行为进行了系统的试验测试，分析了其塑性流动行为中出现的反常应力峰及其波动行为，并尝试揭示其微观机理。基于镍基高温合金双相结构及其塑性流动行为中反常应力峰波动行为的微观机理，建立了包含镍基高温合金塑性流动行为中反常应力峰及其波动行为的金属热黏塑性本构关系，所建立本构关系可以很好的预测镍基高温合金塑性流动行为。通过本项目的研究，为镍基高温合金的工程应用提供了理论和试验依据。