Monday, 11 October 2004 - 4:45 PM

This presentation is part of : Graduate Student Competition

Heat treating of commercial Ni-rich NiTi shape memory alloys for manufacturability

Jeffrey Tyber1, Carl P. Frick1, Alicia M. Ortega1, Ken Gall1, and Hans J. Maier2. (1) University of Colorado at Boulder, Boulder, CO 80309, (2) Institute für Werkstoffkunde, University of Paderborn, Paderborn, 33098, Germany

The purpose of this study is to determine at what heat treatment Nickel Titanium (NiTi) becomes solutionized. Currently, the majority of the studies in the shape memory field use a 1000oC for 1 hour heat treatment to solutionize NiTi. This heat treatment will lead to the increased chance of oxidation and is not always readily available due to the high temperature requirements. Polycrystalline Ti-50.9 at.% Ni was commercially hot rolled between 845-955 oC which caused dynamic recovery and recrystallization, as well as, suppressed precipitate formation. The hot rolled material was then heat treated for 1.5 hours at 600oC heat treatment and the conventional 1000oC heat treatment. Stress-strain behavior was investigated for the “as received” NiTi, in addition to the heat treated NiTi. The results illustrate all three materials were capable of pseudoelastic behavior at room temperature with only minor differences between the “as received” and the 600oC; implying a solutionizing heat treatment may not be necessary subsequent to hot working. Transmission Electron Microscopy pictures revealed extremely small precipitates (>>10nm) and relatively few dislocations for the “as received” and heat treated NiTi. The outcome of this study will have a great effect on the machining, manufacture, and economic viability of using NiTi in various applications.

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