Master of Science
Materials Science and Engineering
John N. DuPont
The solidification and weldability of nickel base alloys that simulate the base composition
range of Alloy 52i with systematic variations of C, N, Nb, Ti, Si, and Mg were studied
using solidification modeling, differential thermal analysis (DTA), microstructural
characterization techniques, and Varestraint weldability testing. The solidification path for
these systems generally follows a primary L → γ reaction, followed by a eutectic-type L
→ (γ + NbC) reaction which results in a smaller solidification temperature range and/or a
eutectic-type L → (γ + Laves) reaction which results in a larger solidification temperature
range. Depending on the C and N concentrations, other carbo-nitride phases can also form.
Increased carbon, lowered niobium, and moderate nitrogen were found to promote Nb-rich
phase formation, prohibit Laves phase formation, and minimize the solidification
temperature range. Increasing niobium, titanium, and nitrogen resulted in large blocky TiN
phases that formed in the dendrite cores and Laves phase formation at the crack tip,
increased solidification temperature ranges, and reduced weldability. Silicon was found to
promote Laves phase formation, increase the solidification cracking range, and increase
solidification cracking susceptibility. In this work, the relation between alloy composition,
solidification behavior, and weldability is described to aid in alloy development of solidification cracking resistant alloys for naval nuclear applications.
Fraser, Allison, "Effect of Alloying Elements on the Solidification Behavior and Weldability of Nickel Base Alloy 52" (2020). Theses and Dissertations. 5653.
Available for download on Friday, January 29, 2021