48. super-elastic response and shape memory behavior in ceramic materials

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: CaliBaja Center for Resilient Materials & Systems
Faculty Advisor(s): Olivia A. Graeve

Primary Student
Name: Hamed Hosseini Toudeshki
Email: hahossei@ucsd.edu
Phone: 619-288-6303
Grad Year: 2018

Super-Elastic Response and Shape Memory Behavior in Ceramic Materials Hamed Hosseini-Toudeshki1, Steven Herrera2, David Kisailus2, Olivia A. Graeve1,* 1Department of Mechanical and Aerospace Engineering University of California, San Diego 9500 Gilman Drive - MC 0411 La Jolla, CA 92093-0411 2Department of Chemical and Environmental Engineering Material Science and Engineering Program University of California, Riverside, CA 92521 MSE Building Room 343 Shape memory behavior is associated with specific materials that can be deformed to different levels of inelastic strain with the ability of returning back to their original shape upon heating. The essential requirement in crystalline materials to possess shape memory behavior is a thermo-elastic martensitic transformation between two crystallographic phases that can be induced thermally (shape memory effect) or by applying stress (super-elasticity). Shape memory ceramics are considered a family of smart materials with unique properties and diverse applications such as mechanical damping systems, actuations and sensors. Comparing with alloys, ceramics offer valuable advantages such as ability to stand and operate at high temperature environments, high toughness and chemical inertness. The major issue with ceramic materials that limits their super-elastic response and shape memory behavior is crack propagation during phase transformation. In fact, relief of residual stresses during reverse martensitic transformation, upon unloading, initiates micro-cracking and twinning. For shape memory alloys, it has been shown that metal micro-pillars plastic behavior is different than the material bulk. In fact, it has been shown that the cracking problem can be eliminated by reducing the sample size to the order of grain size. With this approach, a structure with large free surface area is created so that mismatch stresses are relaxed. In this study, we are investigating the super-elastic response and shape memory behavior of LaNbO4 ceramic materials utilizing nano-indentation. The material is synthesized and a densification process is performed utilizing the spark plasma sintering technique. To avoid mismatch stresses during phase transformation, experiments have been performed at micro scale sizes, in the order of grain sizes, on micro-pillars milled away from bulk ceramic using focused ion beam technology. Interestingly, two different super-elastic responses have been observed (instantaneous step-like response and wavy rubber-like behavior) on single-crystal and poly-crystal pillars. A combination of super-elastic cycles up to 5% recoverable compressive strain and pseudo-elastic responses up to 10% were achieved during the micro-compression experiments. Experimental results are compared with theoretical domain transformation models for LaNbO4. *Contact author (Email: ograeve@ucsd.edu, URL: http://graeve.ucsd.edu)

Industry Application Area(s)
Aerospace, Defense, Security | Civil/Structural Engineering | Materials

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