Analysis of multistep transformations in single-crystal NiTi

A. J.Wagoner Johnson, Reginald Felix Hamilton, H. Sehitoglu, G. Biallas, H. J. Maier, Y. I. Chumlyakov, H. S. Woo

Research output: Contribution to journalArticle

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Abstract

The effects of composition and heat treatment on the thermally induced phase-transformation behavior of single-crystal NiTi with compositions of 50.1, 50.4, 50.8, and 51.5 at. pct Ni are presented in this article. Differential scanning calorimetry (DSC) experiments reveal that a heat-treated 50.1 at. pct Ni alloy exhibits an unprecedented multiple-step transformation (MST) on both heating and cooling, with up to four peaks. This behavior is absent in the higher-Ni-content alloys. In polycrystalline NiTi alloys, MSTs have been attributed to microstructure heterogeneities such as grain boundaries and dislocations, which influence precipitation. In-situ scanning electron microscopy (SEM) results show that the MST in the 50.1 at. pct Ni alloy is associated with single-crystal defects such as dendrites and low-angle boundaries. A heterogeneous precipitate distribution is observed in transmission electron microscopy (TEM) images of the same low-Ni alloy, also associated with the defects, creating conditions that have been shown in other studies to promote the MST in polycrystals. These MSTs are not observed for high-Ni single-crystal alloys containing the same defects. In this article, we describe the origin of the extraordinary forward and reverse MSTs in the low-Ni alloy and the absence of the MST in high-Ni alloys. Transformation sequences are proposed based on the contrasting precipitate microstructures.

Original languageEnglish (US)
Pages (from-to)919-928
Number of pages10
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume36
Issue number4
StatePublished - Apr 1 2005

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Single crystals
single crystals
Precipitates
precipitates
Defects
microstructure
Microstructure
Dendrites (metallography)
Crystal defects
defects
Polycrystals
polycrystals
dendrites
Chemical analysis
Dislocations (crystals)
crystal defects
phase transformations
Differential scanning calorimetry
Grain boundaries
heat treatment

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

Cite this

Johnson, A. J. W., Hamilton, R. F., Sehitoglu, H., Biallas, G., Maier, H. J., Chumlyakov, Y. I., & Woo, H. S. (2005). Analysis of multistep transformations in single-crystal NiTi. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 36(4), 919-928.
Johnson, A. J.Wagoner ; Hamilton, Reginald Felix ; Sehitoglu, H. ; Biallas, G. ; Maier, H. J. ; Chumlyakov, Y. I. ; Woo, H. S. / Analysis of multistep transformations in single-crystal NiTi. In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. 2005 ; Vol. 36, No. 4. pp. 919-928.
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Johnson, AJW, Hamilton, RF, Sehitoglu, H, Biallas, G, Maier, HJ, Chumlyakov, YI & Woo, HS 2005, 'Analysis of multistep transformations in single-crystal NiTi', Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, vol. 36, no. 4, pp. 919-928.

Analysis of multistep transformations in single-crystal NiTi. / Johnson, A. J.Wagoner; Hamilton, Reginald Felix; Sehitoglu, H.; Biallas, G.; Maier, H. J.; Chumlyakov, Y. I.; Woo, H. S.

In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 36, No. 4, 01.04.2005, p. 919-928.

Research output: Contribution to journalArticle

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AU - Johnson, A. J.Wagoner

AU - Hamilton, Reginald Felix

AU - Sehitoglu, H.

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AU - Maier, H. J.

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N2 - The effects of composition and heat treatment on the thermally induced phase-transformation behavior of single-crystal NiTi with compositions of 50.1, 50.4, 50.8, and 51.5 at. pct Ni are presented in this article. Differential scanning calorimetry (DSC) experiments reveal that a heat-treated 50.1 at. pct Ni alloy exhibits an unprecedented multiple-step transformation (MST) on both heating and cooling, with up to four peaks. This behavior is absent in the higher-Ni-content alloys. In polycrystalline NiTi alloys, MSTs have been attributed to microstructure heterogeneities such as grain boundaries and dislocations, which influence precipitation. In-situ scanning electron microscopy (SEM) results show that the MST in the 50.1 at. pct Ni alloy is associated with single-crystal defects such as dendrites and low-angle boundaries. A heterogeneous precipitate distribution is observed in transmission electron microscopy (TEM) images of the same low-Ni alloy, also associated with the defects, creating conditions that have been shown in other studies to promote the MST in polycrystals. These MSTs are not observed for high-Ni single-crystal alloys containing the same defects. In this article, we describe the origin of the extraordinary forward and reverse MSTs in the low-Ni alloy and the absence of the MST in high-Ni alloys. Transformation sequences are proposed based on the contrasting precipitate microstructures.

AB - The effects of composition and heat treatment on the thermally induced phase-transformation behavior of single-crystal NiTi with compositions of 50.1, 50.4, 50.8, and 51.5 at. pct Ni are presented in this article. Differential scanning calorimetry (DSC) experiments reveal that a heat-treated 50.1 at. pct Ni alloy exhibits an unprecedented multiple-step transformation (MST) on both heating and cooling, with up to four peaks. This behavior is absent in the higher-Ni-content alloys. In polycrystalline NiTi alloys, MSTs have been attributed to microstructure heterogeneities such as grain boundaries and dislocations, which influence precipitation. In-situ scanning electron microscopy (SEM) results show that the MST in the 50.1 at. pct Ni alloy is associated with single-crystal defects such as dendrites and low-angle boundaries. A heterogeneous precipitate distribution is observed in transmission electron microscopy (TEM) images of the same low-Ni alloy, also associated with the defects, creating conditions that have been shown in other studies to promote the MST in polycrystals. These MSTs are not observed for high-Ni single-crystal alloys containing the same defects. In this article, we describe the origin of the extraordinary forward and reverse MSTs in the low-Ni alloy and the absence of the MST in high-Ni alloys. Transformation sequences are proposed based on the contrasting precipitate microstructures.

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