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Instrumented Nanoindentation Studies Of Deformation In Shape Memory Alloys, Sudhir Rajagopalan
Instrumented Nanoindentation Studies Of Deformation In Shape Memory Alloys, Sudhir Rajagopalan
Electronic Theses and Dissertations
Near equi-atomic nickel titanium (NiTi) shape memory alloys (SMAs) are a class of materials characterized by their unique deformation behavior. In these alloys, deformation mechanisms such as mechanical twinning and stress induced phase transformation between a high symmetry phase (austenite) and a low symmetry phase (martensite) additionally occur and influence mechanical behavior and thus their functionality. Consequently, applications of SMAs usually call for precise phase transformation temperatures, which depend on the thermomechanical history and the composition of the alloy. Instrumented indentation, inherently a mechanical characterization technique for small sampling volumes, offers a cost effective means of empirically testing SMAs in …
Diffraction Studies Of Deformation In Shape Memory Alloys And Selected Engineering Components, Chandrasen Rathod
Diffraction Studies Of Deformation In Shape Memory Alloys And Selected Engineering Components, Chandrasen Rathod
Electronic Theses and Dissertations
Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated …