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Type Yoon, Kevin Eylhan
  Publication Temporal Evolution of the Chemistry and Nanostructure of Multicomponent Model Ni-Based Superalloys Volume Book Whole
Pages 2004
  Abstract  
  Corporate Author  
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  Summary Language 189 Series Editor  
Abbreviated Series Title Ni-based superalloys are critical materials in the aerospace industry because of their excellent balance of mechanical properties including the elevated-temperature strength, which is a result of the dual-phase microstructure, consisting of the Ni-rich γ-matrix (FCC) and γ'-precipitates (L12 structure). It is critical to understand the effects of each alloying element on the microstructure of Ni-based superalloys in order to further improve the mechanical properties, which are direct consequences of the microstructure. Nanoscale chemistry, nanostructure, and temporal evolution of several Ni-based superalloys, ranging from a simple model Ni-Cr-Al ternary alloy to a complex commercial superalloy, René N6, have been investigated utilizing three-dimensional atom probe (3DAP) microscopy and conventional transmission electron microscopy (CTEM). First, this research demonstrates the power of 3DAP microscopy, which can analyze the chemistry of the complex commercial superalloy, René N6, with nine elements. Concentration profiles and proximity histogram were obtained displaying the partitioning behavior of all alloying elements and especially Re interfacial segregation at the γ/γ' interface. Next, a model Ni-based superalloy, Ni-Cr-Al alloy, was studied as a reference for the study of a more complex quaternary alloy, Ni-Cr-Al-Re alloy. The temporal evolution of chemistry and nanostructure of the alloy are determined employing 3DAP microscopy. The coarsening kinetics of the γ'-precipitates is examined and compared with theory, which is in partial agreement. A new coarsening mechanism has been suggested which explains the difference between the experimental results and the theoretical predictions. In addition, experimental results are also compared with the results of kinetic Monte Carlo (KMC) simulations. Finally, the effects of a Re addition on the temporal evolution of chemistry and microstructure of the Ni-Cr-Al alloy and coarsening kinetics of the γ'-precipitates have been investigated employing 3DAP microscopy and CTEM. The Re addition stabilizes the spheroidal morphology of the γ'-precipitates for extended aging times and retards the coarsening kinetics without any Re interfacial segregation. The coarsening kinetics is also compared with the theory.
  Series Issue ISSN Northwestern University  
Medium Ph.D. thesis
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no NU @ karnesky @ 15
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