Microstructural degratation of the single-crystal superalloy CMSX-4-during annealing under load: Implementation of rafting kinetics in mechanical modelling.

在高温使用过程中，镍基高温合金的y/y组织变得不稳定：立方的y析出物聚集成膨胀的y-筏。由于漂流，机械性能急剧下降。建议在模拟燃气轮机中广泛使用的高温合金CMSX-4的力学行为时考虑漂流的影响。这将分三个步骤完成：漂流动力学的研究，作为变形/应力状态和温度的函数的漂流的数学描述，将该函数实现为力学模型。将在825-1050°C的宽温度范围内模拟飞机和动力燃气轮机的运行条件，在低应力下研究漂流动力学。将采用一种新的试件设计(平面楔形)。它的优点是：平坦度允许在多次加载-退火试验后重新准备同一试件的表面，以便通过扫描电子显微镜和X射线衍射仪研究其微观结构变化；楔形形状提供沿试件轴线的线性应力变化。这些调查的结果将是确定漂流的演化规律。由此得到的本构定律将考虑漂流引起的力学性能退化，从而允许在发生漂流的服役条件下对叶片进行有限元分析。

During high temperature service the y/y -microstructure of nickel-base superalloys becomes unstable: the cuboidal y precipitates coalesce into expanded y -rafts. Mechanical properties strongly degrade due to rafting . It is proposed to include the effect of rafting into modelling the mechanical behaviour of superalloy CMSX-4 widely used in gas turbines. This will be done in three steps: investigation of the rafting kinetics, mathematical description of rafting as a function of the deformation/stress state and the temperature, implementation of this function into a mechanical model. The rafting kinetics will be investigated at low stresses over a wide temperature range 825-1050°C simulating the operating conditions of aircrafts and power gas turbines. A new specimen design (flat wedge shape) will be applied. Its advantages are: the flatness allows preparing the surface of the same specimen anew after multiple load-annealing tests for investigation of the microstructual change by SEM and XRD; the wedge shape provides a linear change of stresses along the specimen axis. The outcome of these investigations will be the identification of an evolution law for rafting. The resulting constitutive law will take into account the degradation of the mechanical properties due to rafting thus allowing the Finite Element analysis of blades under service conditions, where rafting occurs.