Tyler Knapp
Advisors: Prof. Aaron Stebner and Prof. Naresh Thadhani

will defend a doctoral thesis entitled,

Thermomechanical Developments of Refractory Binary Niobium-Ruthenium Shape Memory Alloys for Ultra-High Temperature Applications

on Tuesday, August 19, 2025
10:00 AM
In-person at MRDC 4211
Or online at: Join the meeting now


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

Abstract
Shape memory alloys can accommodate relatively large strains without permanent deformation due to a reversible martensitic solid-state phase transformation. Equiatomic NbRu shape memory alloys have shown to undergo two reversible phase transformations from ’’ to ’ to  (monoclinic to tetragonal to cubic) up to temperatures exceeding 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 tetragonal phase is present at room temperature. Previous literature established that this alloy system could function in high temperature environments, where previous NiTi-based shape memory alloys have failed to achieve an acceptable work output.
For a shape memory alloy to be effective, it must be mechanically strong, output work while under load, and have a consistent and easily reversible thermomechanical response at the operating temperature ranges necessary. Previous literature on NbRu only shows the two reversible martensitic solid-state phase transformation happening across different binary compositions, the crystal structures associated with each phase, and some preliminary mechanical loading tests. These papers do not quantify the extent of uniaxial strain recovery by this alloy system, how stress of the material affects transformation temperatures, or to what extent superelasticity is possible.
This work further develops the process-structure-property relationships of binary NbRu and investigates the effects of stress and composition on the transformation temperatures of this binary alloy. This work focuses on 51-55 at% Nb alloys and quantifies their properties through stress-free differential scanning calorimetry (DSC), in-situ X-Ray Diffraction (XRD), ultra-high temperature mechanical testing, and load-biased thermal cycling. The goal of this research is to further the knowledge about the behavior of this alloy and how feasible it is to apply it to ultra-high temperature applications such as solid-state gaskets, actuators, and dampers. With more knowledge about this alloy, we can help better inform computer modeling, ternary alloying, and preprocessing studies about the capabilities and possibilities of this alloy.