Nanoscale studies of shape memory and superelastic properties of dual-phase shape memory alloys
Loading...
Authors
Dar, Rebecca Dorothy
Issue Date
2016-08
Type
Electronic thesis
Thesis
Thesis
Language
ENG
Keywords
Materials engineering
Alternative Title
Abstract
Co-Ni-Al is the primary model system selected for experimental studies. In nanoindentation tests using a Berkovich tip (~150 nm radius), enhanced strain recovery, superelastic recovery, and hardness are observed in austenite volume adjacent to its interface with precipitate as compared to other regions tested. A larger radius conospherical tip (~831 nm radius) produces less unrecoverable deformation, thereby enabling a larger portion of material to transform reversibly and is employed in nanoindentation tests in austenite β adjacent to intergranular precipitate, austenite β adjacent to bare grain boundaries, and in austenite β interior. Austenite interfaces adjacent to precipitate have the lowest energy dissipation, the highest hardness, and the highest strain recovery compared to β regions adjacent to bare grain boundaries or β interior. The ductile second phase improves superelasticity by plastically accommodating transformation strain from stress-induced martensitic transformation in its adjacent volume, alleviating stress concentration and relieving constraint on transforming austenite. As a result, a greater portion of austenite transforms reversibly and higher strain recovery is observed in austenite adjacent to the second phase. These results enable design of dual-phase microstructures with enhanced ductility, high recoverable strain, and high hardness for several applications, such as mechanical actuation, damping, and those which apply high loads to materials.
Description
August 2016
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY