Master of Science (MS)
Materials Science and Engineering
First Advisor's Name
First Advisor's Committee Title
Second Advisor's Name
Second Advisor's Committee Title
Third Advisor's Name
Third Advisor's Committee Title
Grade 91 steel, Creep resistance, Ferritic-Martensitic steels, Welding microstructure, Computational thermodynamics, Secondary phase, Alloy composition
Date of Defense
Grade 91 (Gr.91) is a common structural material used in boiler applications and is favored due to its high temperature creep strength and oxidation resistance. Under cyclic stresses, the material will experience creep deformation eventually causing the propagation of type IV cracks within its heat-affected-zone (HAZ) which can be a major problem under short-term and long-term applications. In this study, we aim to improve this premature failure by performing a computational thermodynamic study through the Calculation of Phase Diagram (CALPHAD) approach. Under this approach, we have provided a baseline study as well as simulations based on additional alloying elements such as manganese (Mn), nickel (Ni), and titanium (Ti). Our simulation results have concluded that high concentrations of Mn and Ni had destabilized M23C6 for short-term creep failure, while Ti had increased the beneficial MX phase, and low concentrations of nitrogen (N) had successfully destabilized Z-phase formation for long-term creep failure.
Smith, Andrew Logan Mr., "Thermodynamic Evaluation and Modeling of Grade 91 Alloy and its Secondary Phases through CALPHAD Approach" (2018). FIU Electronic Theses and Dissertations. 3773.
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