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

经过几十年的实施，镍基单晶高温合金在燃气轮机热段中发挥的作用仍然是必不可少的。只有通过(1)接近实际的实验装置、(2)提供可靠实验数据的表征方法和(3)以这些数据为输入的寿命和变形预测模型之间的相互作用，才能在这类材料的耐高温方面取得进一步的进展。在拟议的项目中，申请人希望对高温合金单晶蠕变性能的提高和理解做出贡献。为此，将在标准试件和圆形缺口试件上进行受控高温蠕变试验，并对其进行表征，这将产生技术上相关的多轴应力条件。具体来说，基于位错的实验技术将通过应用新开发的扫描电子显微镜(STEM)位错分析方法来描述导致镍基高温合金单晶LEK 94高温蠕变行为的微观机制。蠕变试验将在1000°C以上的温度下对缺口试件进行。重点讨论以下几点：(1)变形的微观机制与应力状态的多轴性的关系；(2)圆形缺口的存在对高温蠕变行为的影响；(3)用实验数据对模拟工具的验证。多轴应力状态下的高温蠕变试验的实验数据将被生成和汇编。评估的数据将包括单个相内的位错类型和密度，并将确定由多轴诱导的微观组织演变并与位错活动相关联。这些数据对于正确验证旨在模拟单晶高温合金蠕变行为的本构方程是必不可少的，这将作为最后一步实施。

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.