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]
-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 . 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 .
 J. Dadda, H.J. Maier, I. Karaman, Y. I. Chumlyakov: Acta Mater. 57 (2009) 6123-6134.
 T. Niendorf, P. Krooß, C. Somsen, G. Eggeler, Y. I. Chumlyakov, H. J. Maier: Acta Mater. 89 (2015) 298.
 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.
 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.
 P. M. Kadletz, P. Krooß, Y.I. Chumlyakov, M. J. Gutmann, W.W. Schmahl, H. J. Maier, T. Niendorf: Mater. Letters 159 (2015) 16.
 X. Ren, K.Otsuka: Nature 389 (1997) 579.