Microstructure-property correlations of a Ni-based single crystal superalloy using computational homogenization

Abstract

The CMSX-4 alloy is widely used as a structural material for turbine blades due to its outstanding thermo-mechanical properties. These properties are governed by the interaction between γ/ γ’ phases of the microstructure. During service, the microstructure can undergo vast changes which have a direct influence on the overall performance of the material. In this thesis, the influence of microstructure changes on the mechanical performance of the macrostructure was studied. This was made possible due to the development of unified multiscale simulation scheme capable of avoiding the labor-intensive integration of several different representative volume elements. For the multiscale method the multilevel Finite Element Method FE2 was applied. It implies the usage of Finite Element Analysis (FEA) on both scales in a semi-concurrent manner. The load for microstructure is provided by macro simulation consequently for every integration point of every element. The response of the microstructure is homogenized and read by the macro simulation. As a base for the FEA the Abaqus commercial solver was chosen, due to its speed and availability of various subroutines. Since the macro simulation requires hours to converge even for the simplest cases, it has been successfully parallelized. This parallelization was thought through for Linux and Windows platforms, due to potential further development of the method as an Abaqus extension. The performance of the multiscale infostructure was confirmed on the seven simplified representative volume elements of γ and γ’. The influence of variation of γ’ phase volume fraction on the mechanical response on the macroscale was studied. Apart from this, the effect of microstructure degradation was also investigated. As it has been shown that the increase of the volume fraction of elastic hardening phase γ’ leads to the overall linear behavior of the model. The applied material model that assumed the pure elastic behavior of the precipitate was found to be insufficient to simulate the macroscale stressstrain curve that would correspond to experimental data. However, the model with a volume fraction of the precipitate similar to the one in CMSX-4 was proven to provide the correct Youngs modulus. The models with degraded microstructures did not show significant deviation in mechanical behavior when compared to the original cuboid model.