Experimental and Simulation Study of the Effect of Precipitation Distribution and Grain Size on the AD730 Ni-Based Polycrystalline Superalloy Tensile Behavior

摘要

The mechanical properties of nickel-based superalloys depend strongly on their microstructure, namely the grain size and the state of precipitation. Main design criteria in aeronautical turbine disks are the resistance to disk burst and low cycle fatigue in the bore, but also to creep in the rim part due to higher temperatures. The chosen microstructures result from a compromise between these contradictory requirements. Indeed, creep durability is improved using a coarse grain microstructure while the increase of static and fatigue strength requires a fine grain microstructure. Moreover, the volume fraction and the size distribution of γ' precipitates are the predominant parameters controlling mechanical properties at lower temperatures. A spatial optimization of the microstructure is reachable using specific technologies, e.g. dual-microstructure heat treatment. The development of microstructure-sensitive models is thus a major concern for the optimal design of these components including gradient of grain size and/or precipitate size. Full-field finite element simulations may be employed to predict the macroscopic behavior of polycrystalline aggregates using crystal plasticity constitutive equations whose parameters depend explicitly on the microstructural attributes. In this framework, the present study is devoted to the evaluation of the yield stress of polycrystalline AD730 nickel-based superalloy, chosen as a model material. This work includes microstructural characterization and mechanical tests carried out on single crystals and polycrystalline specimens with well-controlled microstructures. Predictions of the macroscopic yield stress are provided by preliminary simulations carried out in the elastic regime combined with a specific post-processing.