Micromechanisms Responsible in Deformation of Nickel-Base Superalloy Single Crystals under Multiaxial Loading at High Temperatures

镍基单晶高温合金在燃气轮机热段中的作用在数十年的应用后仍然至关重要。在这类材料的耐高温性领域的进一步进展只能通过（1）接近现实的实验装置、（2）提供可靠实验数据的表征方法和（3）使用该数据作为输入的寿命和变形预测模型之间的相互作用来实现。在所提出的项目中，申请人希望有助于促进、理解、从而改善高温合金单晶的蠕变性能。为此，将对标准试样和带有圆形切口的试样进行受控高温蠕变试验，并对其进行表征，该试验可产生技术相关的多轴应力条件。具体而言，实验位错为基础的技术应通过应用新开发的方法进行位错分析的扫描透射电子显微镜模式（STEM）来描述的微观机制负责高温蠕变行为的镍基高温合金单晶LEK 94。蠕变试验将在高于1000°C的温度下对缺口试样进行。重点将放在以下几点：（1）涉及变形的微观机制对应力状态的多轴性的依赖性，（2）高温蠕变行为的圆形缺口的存在的影响和（3）模拟工具与实验数据的验证。将生成和编译一组多轴应力状态下高温蠕变试验的实验数据。评估的数据将包括各个相内的位错类型和密度，并且将确定由多轴性引起的微观结构演化并将其与位错活动相关联。这些数据是必要的适当验证的本构方程打算模型单晶高温合金的蠕变行为，这将是实施的最后一步。

The role played by Ni-based single crystal superalloys in hot sections of gas turbines remains essential after decades of implementation. Further progress in the area of high temperature resistance of this materials class can only be achieved through the interaction between (1) close-to-reality experimental setups, (2) characterization methods that provide reliable experimental data and (3) life and deformation prediction models that use this data as input.In the proposed project the applicant wishes to contribute to the advancement, the understanding, and thus the improvement of creep performance of superalloy single crystals. To this end, controlled high temperature creep tests will be performed and characterized on standard specimens and on specimens with a circular notch, which generates technically relevant multiaxial stress conditions. Specifically, experimental dislocation-based techniques shall be conducted by applying a newly developed methodology for dislocation analysis in the scanning transmission electron microscopy mode (STEM) to describe the micromechanisms responsible for high temperature creep behavior of the Ni-based superalloy single crystal LEK 94. Creep tests will be conducted at temperatures above 1000°C on the notched specimens. Focus will be set on the following points: (1) the dependence of micromechanisms involved in deformation on the multiaxiality of the stress state, (2) the effect of the presence of a circular notch on high temperature creep behavior and (3) the validation of simulation tools with experimental data obtained. Experimental data from a set of creep tests in the high temperature regime under multiaxial stress state will be generated and compiled. The data evaluated will comprise dislocation types and densities within the individual phases and microstructural evolution induced by multiaxiality will be determined and correlated with the dislocation activity. This data is essential for proper validation of constitutive equations intended to model creep behavior of monocrystalline superalloys, which will be implemented as a last step.