Knoxville, TN, United States
Knoxville, TN, United States

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Teng Z.K.,University of Tennessee at Knoxville | Zhang F.,CompuTherm LLC | Miller M.K.,Oak Ridge National Laboratory | Liu C.T.,University of Tennessee at Knoxville | And 8 more authors.
Materials Letters | Year: 2012

NiAl-type precipitate-strengthened ferritic steels have been known as potential materials for the steam turbine applications. In this study, thermodynamic descriptions of the B2-NiAl type nano-scaled precipitates and body-centered-cubic (BCC) Fe matrix phase for four alloys based on the Fe-Al-Ni-Cr-Mo system were developed as a function of the alloy composition at the aging temperature. The calculated phase structure, composition, and volume fraction were validated by the experimental investigations using synchrotron X-ray diffraction and atom probe tomography. With the ability to accurately predict the key microstructural features related to the mechanical properties in a given alloy system, the established thermodynamic model in the current study may significantly accelerate the alloy design process of the NiAl-strengthened ferritic steels. © 2011 Elsevier B.V. All rights reserved.


Teng Z.K.,University of Tennessee at Knoxville | Zhang F.,CompuTherm LLC | Miller M.K.,Oak Ridge National Laboratory | Liu C.T.,University of Tennessee at Knoxville | And 8 more authors.
Intermetallics | Year: 2012

Two critical issues restricting the applications of NiAl precipitate-strengthened ferritic steels are their poor room temperature ductility and insufficient creep resistance at temperatures higher than 600 °C. In this study, a thermodynamic modeling approach is integrated with experiments focused on investigating the ductility and creep resistance of steel alloys based on the Fe-Ni-Al-Cr-Mo multi-component system. The mechanical property studies showed that the creep resistance increases with increasing the volume fraction of B2-ordered precipitates, while the opposite trend was observed for the ductility. Low solubility of Al in the α-Fe matrix was found to favor a ductility increase. Thermodynamic calculations were used to predict the volume fraction of B2-ordered precipitate and the elemental partitioning to guide the selection of alloy compositions that might exhibit the balanced creep resistance and ductility. Key experiments were then conducted to validate the prediction. This integrated approach was found to be very effective in the alloy development. © 2012 Elsevier Ltd. All rights reserved.

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