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dc.contributor.advisorChristopher A. Schuh.en_US
dc.contributor.authorLai, Alan, Ph. D. Massachusetts Institute of Technologyen_US
dc.contributor.otherMassachusetts Institute of Technology. Department of Materials Science and Engineering.en_US
dc.date.accessioned2016-09-13T18:06:04Z
dc.date.available2016-09-13T18:06:04Z
dc.date.copyright2016en_US
dc.date.issued2016en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/104111
dc.descriptionThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.en_US
dc.descriptionThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.en_US
dc.descriptionCataloged from student-submitted PDF version of thesis.en_US
dc.descriptionIncludes bibliographical references (pages 133-139).en_US
dc.description.abstractShape memory ceramics rely on martensitic transformations which are similar to those found in metallic shape memory materials, but ceramics offer several advantages over metals such as higher operating temperatures and larger transformation stresses. However, polycrystalline shape memory ceramics have shown poor cycling performance which limits their use in practical applications. This is due to the inherent physical constraints of the grains that create stress concentrations and eventually leads to intergranular fracture. Here it is proposed that single crystalline and oligocrystalline ceramics-made with a single grain or very few grains-will avoid the physical constraints found in polycrystalline materials that lead to intergranular fracture and result in shape memory ceramics with enhanced cycling performance. Zirconia was chosen for study because it has the necessary martensitic transformations and has shown limited shape memory properties when in the bulk polycrystalline form. Focused ion beam milling was used to make single crystal and oligocrystal pillars of varying diameter that were compression tested using a nanomechanical testing platform to determine the mechanical properties. This work showed that removing grain constraints in micron-scale shape memory zirconia prevented cracking and fracture. It also enhanced the number of achievable repeatable cycles from five in bulk materials to at least hundreds in small structures. The transition from single- to oligo- to poly-crystal was explored and it was found that fracture is more likely in polycrystals and that the transformation stresses increase as pillar diameter is increased, the opposite of what is observed in shape memory metals. This phenomenon is attributed to the higher stiffness of ceramics making the stored elastic energy more important. The effect of crystal orientation was investigated to aid in design and optimization. Orientation maps were produced for fracture behavior, elastic modulus, transformation stress, and transformation strain. Finally four different scale-up architectures were proposed and implemented - powders, wires, foams, and thin films - and each demonstrated shape memory properties thereby paving the way for deployment in practical applications.en_US
dc.description.statementofresponsibilityby Alan Lai.en_US
dc.format.extent139 pagesen_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectMaterials Science and Engineering.en_US
dc.titleShape memory ceramics in small volumesen_US
dc.typeThesisen_US
dc.description.degreePh. D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Materials Science and Engineering.en_US
dc.identifier.oclc958136028en_US


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