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On the Role of atomic Ordering on functional Fatigue of Co-Ni-Ga High-Temperature Shape Memory Single Crystals

Thursday (29.09.2016)
12:30 - 12:45
Part of:

Superelastic Co-Ni-Ga high-temperature shape memory alloys (HT-SMA) are characterized by a wide range of adjustable transformation temperatures and lower costs than Ni-Ti-(Pd, Pt, ...) HT-SMA, which renders them attractive for high-temperature applications in automotive and aerospace industries. [1,2]

[001]-oriented single crystals show fully recoverable transformation strains up to 4.3 % under compressive and up to 8.5 % under tensile loads in superelastic single-cycle tests [3,4]. Up to 180 °C test temperature the alloy shows perfect cyclic stability; cyclic testing at higher temperatures leads to functional fatigue, i.e. accumulation of permanent strain and decrease of critical stress for phase transformation [3,4].

In recent studies [3-5] two major fatigue mechanisms could be identified. At 300°C, as found by neutron diffraction and TEM, fatigue is related to the formation of residual martensite mainly induced by an increased dislocation activity [3]. At 400°C fatigue is dominated by a different process: neutron diffraction experiments revealed a change of atomic order linked to martensite stabilization in Co49Ni21Ga30 single crystals [4,5]. This finding represents the first experimental evidence for the concept of 'symmetry-conforming short-range order' stated by Ren and Otsuka in 1997 [6].

[1] J. Dadda, H.J. Maier, I. Karaman, Y. I. Chumlyakov: Acta Mater. 57 (2009) 6123-6134.

[2] T. Niendorf, P. Krooß, C. Somsen, G. Eggeler, Y. I. Chumlyakov, H. J. Maier: Acta Mater. 89 (2015) 298.

[3] P. Krooß, T. Niendorf, P. M. Kadletz, C. Somsen, M.J. Gutmann, Y. I. Chumlyakov, W. W. Schmahl, G. Eggeler, H. J. Maier: Shap. Mem. Superelasticity 1 (2015) 6.

[4] P. Krooß, P.M. Kadletz, C. Somsen, M. J. Gutmann, Y.I. Chumlyakov, W.W. Schmahl, G. Eggeler, H. J. Maier, T. Niendorf: Shap. Mem. Superelasticity 2 (2016) 37–49.

[5] P. M. Kadletz, P. Krooß, Y.I. Chumlyakov, M. J. Gutmann, W.W. Schmahl, H. J. Maier, T. Niendorf: Mater. Letters 159 (2015) 16.

[6] X. Ren, K.Otsuka: Nature 389 (1997) 579.

Additional Authors:
  • Philipp Krooß
    Universität Kassel
  • Dr. Christoph Somsen
    Ruhr Universität Bochum
  • Dr. Matthias J. Gutmann
    Rutherford Appleton Laboratory
  • Prof. Dr. Yuri I. Chumlyakov
    Tomsk State University
  • Prof. Dr. Gunther Eggeler
    Ruhr Universität Bochum
  • Prof. Dr. Wolfgang W. Schmahl
    Ludwig-Maximilians-Universität München
  • Prof. Dr. Hans J. Maier
    Leibniz Universität Hannover
  • Prof. Dr. Thomas Niendorf
    Universität Kassel