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Characterization of NiTi Shape Memory Wires by Differential Scanning Calorimetry and Transmission X-ray Diffraction

Published online by Cambridge University Press:  25 February 2011

Ming-Yuan Kao ,
Sepehr Fariabi ,
Paul E. Thoma ,
Husnu Ozkan  and
Louis Cartz
Ming-Yuan Kao
Affiliation:
Johnson Controls, Inc., P.O.Box 591, Milwaukee, WI 53201
Sepehr Fariabi
Affiliation:
Johnson Controls, Inc., P.O.Box 591, Milwaukee, WI 53201. Currently with ACS Inc., P.O.Box 58167, Santa Clara, CA 95052
Paul E. Thoma
Affiliation:
Johnson Controls, Inc., 507 E. Michigan Street, Milwaukee, WI 53202
Husnu Ozkan
Affiliation:
Marquette University, Milwaukee, WI 53233. Currently with Middle East Technical University, Ankara, Turkey 06531
Louis Cartz
Affiliation:
Marquette University, Milwaukee, WI 53233
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Abstract

The reversible transformations between the Austenite (A) and Martensite (M) phases of NITI shape memory wires having a 78°C austenlte finish temperature (950°C annealed) were studied In the cold work and heat treatment ranges between 14 to 62% and 400 to 525°C respectively. The ranges of peak Transformation Temperatures (TI), determined by Differential Scanning Calorimetry (DSC) at a 10°C/min rate, were found to be 56 to 75°C, -28 to 33°C, and 38 to 52°C for the respective high temperature A, low temperature M, and the Intermediate Rhombohedral (R) phases. The degree of cold work and heat treatment had significant effects on the TT of NITI wires. The peak TT of A and M decreases with Increasing cold work. Except for the 14% cold worked wires, the peak TT Increases with Increasing heat treatment temperature for M, and Increases with Increasing heat treatment temperature for A for temperatures higher than 450°C. The peak IT of R Increases with Increasing cold work and decreasing heat treat temperature.

Using MoKα radiation, transmission x-ray diffraction analysis was utilized to determine the phases at room temperature on wires thinned down to 0.05 to 0.01 mm in diameter. The diffraction patterns of body-centered cubic austenite (132) and monodlinic martenslte (B19) for NITi were both Identified. In addition, extra diffraction lines observed for various samples were tentatively assigned to M and the Intermediate R-phase. Depending on the thermal history and the processing conditions, the NITI wires consist of either a pure M, a mixture of A and R, or a mixture of A, R, and M at room temperature.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 246: Symposium M – Shape-Memory Materials and Phenomena--Fundamental Aspects and Applications , 1991 , 225
Copyright
Copyright © Materials Research Society 1992

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References

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