Wednesday, 13 October 2004 - 10:05 AM

This presentation is part of : Active Materials

Cast NiTi Shape Memory Alloys

Alicia M. Ortega1, Carl P. Frick2, Jeffrey Tyber2, Ken Gall2, and Hans J. Maier3. (1) University of Colorado at Boulder, Boulder, CO 80309, (2) University of Colorado, Boulder, CO 80309, (3) Institute für Werkstoffkunde, University of Paderborn, Paderborn, 33098, Germany

Nickel-Titanium’s unique shape memory behavior has made it an ideal candidate for many applications ranging from use in biomedical devices to large restrainer bars in civil infrastructure. Almost all of these applications make use of Nickel-Titanium (NiTi) that has been formed through a deformation process (like cold-drawing). However these deformation processes are often times a costly additional processing step. Thus it would be desirable to find a way to process the material for its various applications with minimal or no deformation processing while still having the material maintain its shape memory behavior. Although direct casting could circumvent these processing steps, the thermo-mechanical properties of NiTi in the cast state are not well known. The purpose of this study is to characterize NiTi in its cast state linking such things as nominal composition, structure, and resulting behavior. Techniques used in this investigation include optical microscopy, x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and tension/compression testing. Parameters to be varied are radial location within the cast ingot, orientation of uniaxial loading, tensile or compressive loading, and heat-treatment of the material. Minimal differences in the thermo-mechanical behavior of the cast material as a function of radial position or orientation of loading were observed. Additionally, the cast material showed recoverable strains on the order of 5% under both tensile and compressive loading. This observed lack of tension/compression asymmetry is due to the random texture found in the cast material.

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