Exploring crystallographic compatibility in polycrystalline Cu-based shape-memory alloys

• Main Author: Payne, Madelyn (Madelyn I.)
• Other Authors: Massachusetts Institute of Technology. Department of Materials Science and Engineering.
• Format: Others
• Language: English
• Published: Massachusetts Institute of Technology 2021
• Subjects: Materials Science and Engineering.
• Online Access: https://hdl.handle.net/1721.1/132913

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June, 2019 === Cataloged from the official PDF version of thesis. === Includes bibliographical references (pages 47-49). === Shape-memory alloys (SMAs) are a class of materials that can recover from apparent permanent strain (on the order of 5%) due to a solid-to-solid phase transformation. It has been recently suggested that SMAs satisfying a set of so-called cofactor conditions possess perfect interface compatibility and additional microstructural flexibility during transformation, which are theorized to result in excellent reversibility. Cu-based SMAs are cheaper than other alternatives, but polycrystalline Cu-based SMAs are unable to withstand many cycles because they are prone to cracking and degradation of functional properties. Previous research has identied improved shape-memory properties in Cu-Al-Ni-Mn SMAs in the oligocrystalline state, but polycrystalline material of the same composition has yet to be characterized. In this thesis, I characterize the compatibility of Cu-Al-Ni-Mn alloys according to the cofactor conditions and correlate these findings with results from superelastic mechanical cycling. Building on this knowledge, I also present a new alloy design that is predicted to meet the cofactor conditions and provides a promising path forward for a functionally stable, low-cost, polycrystalline Cu-based SMA. === by Madelyn Payne. === S.B. === S.B. Massachusetts Institute of Technology, Department of Materials Science and Engineering