Committee:

Prof. Aaron Stebner, MSE/ME (advisor)

Prof. Naresh Thadhani, MSE

Prof. Josh Kacher, MSE

Prof. Richard Neu, ME/MSE

Dr. Othmane Benafan, NASA GRC

OPTIMIZATION OF A REFRACTORY NIOBIUM-RUTHENIUM SHAPE MEMORY ALLOY FOR HIGH TEMPERATURE APPLICATIONS

Abstract

Shape memory alloys can accommodate relatively large strains without permanent deformation due to a reversible martensitic solid phase transformation. Equiatomic NbRu shape memory alloys have shown to undergo two reversible phase transformations from b’’ to b’ to b (monoclinic to tetragonal to cubic) at temperatures ranging up to about 800°C. By increasing the relative content of Nb in the alloy, the transformation temperatures of the forward and reverse martensitic transformations have been shown to drastically decrease, even to a point where the cubic phase is not present even at room temperature. The current literature around this material shows it would be worth studying how this alloy system could function in high temperature environments, where previous NiTi-based shape memory alloys have failed to achieve an acceptable work output.

This work aims to fully explore the thermomechanical behavior of NbRu and study how mechanical processing, heat treatments, and ternary alloying elements will affect the alloy’s performance. The work also plans to study how the alloy system responds to high-strain rate loading. Thus far this work has focused on 51-55 at% Nb alloys and measured their properties through stress-free differential scanning calorimetry (DSC), in-situ X-Ray Diffraction (XRD), and thermomechanical cycling. Further testing on alloys that have undergone various processing steps or had a ternary alloying elements added are still needed. By then end of the project, we will know more about the behavior of this alloy and how feasible it is to apply it to high temperature applications such as solid-state gaskets.