"Microsegregation in Single Crystal Ni-based Superalloys and Its Role in TCP Phase Formation" 

Juliana Alvarenga Santos Silva, MSE PhD Candidate 

Advisors: Professors David Johnson & Matthew Krane

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ABSTRACT

Jet engines turbine blades make use of single crystal Ni-based for their manufacturing. However, the presence of TCP (topologically closed-packed) phases, specifically σ and µ phases, can be harmful to the fatigue and creep properties that these components often need to withstand in service. Microsegregation during directional solidification can cause the precipitation of such phases in these types of alloys. This paper examines the fundamentals of microsegregation on the formation of TCP phases, focusing on 2 different superalloys (CMSX-4 and René N6). The existing models for the correlation between the microsegregation and the prediction of TCP precipitation are also evaluated regarding their assumptions, accuracy, and limitations. Possible solutions for this problem are proposed and evaluated, such as changes in the initial composition of the alloys, optimizing the processing parameters, and heat treatments. In conclusion, accurate partition coefficient values are necessary to use microsegregation models to predict the TCP phases. The heat treatment time has an impact on these phases' precipitation as well, and the existing models still deviate from reality.