Pseudoelasticity and cyclic stability in Co49Ni21 Ga30 shape-memory alloy single crystals at ambient temperature

J. Dadda, H. J. Maier, D. Niklasch, I. Karaman, H. E. Karaca, Y. I. Chumlyakov

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


As-grown Co49Ni21Ga30 [001]- and [123]-oriented single crystals were subjected to cyclic compression loading at room temperature above the austenite finish temperature of 15 °C. Strain-controlled experiments were performed using both incremental strain steps and constant strain amplitudes. Cyclic deformation with a maximum strain amplitude of 2.5 pct resulted in rapid accumulation of irrecoverable strains in the [123]-oriented crystals. However, after a few cycles, the samples demonstrated cyclic stability with fully recoverable transformation. By contrast, the [001]-oriented crystals displayed excellent cyclic stability with hardly any change in stress-strain characteristics. In-situ optical microscopy and electron backscattered diffraction analysis were employed to clarify the events that take place at different stages of a typical loading-unloading history. The in-situ observations also revealed that the initiation and growth characteristics of stress-induced martensite (SIM) are heterogeneous on the microscopic scale in CoNiGa alloys. In addition, theoretical transformation and detwinning strains, and resolved shear stress factors (RSSFs), were calculated based on the energy minimization theory and are compared to the experimentally obtained orientation-dependent transformation stress and strain levels. It is shown that the selection of an appropriate orientation is one of the key criteria to optimize the pseudoelastic (PE) response and cyclic stability of CoNiGa alloys.

Original languageEnglish
Pages (from-to)2026-2039
Number of pages14
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Issue number9
StatePublished - Sep 2008

Bibliographical note

Funding Information:
The present study was supported by Deutsche For-schungsgemeinschaft, United States Army Research Office, Contract No W911NF-06-1-0319, and the United States Civilian Research and Development Foundation, Grant No RUE1-2690-TO-05.

ASJC Scopus subject areas

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


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