Date

1-1-2020

Document Type

Thesis

Degree

Master of Science

Department

Materials Science and Engineering

First Adviser

John N. DuPont

Abstract

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.

Available for download on Friday, January 29, 2021

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