Investigations of the ferromagnetic shape memory alloy Co-Ni-Al by X-ray Kossel microdiffraction

Abstract The ternary compound Co-Ni-Al was investigated by the X-ray Kossel microdiffraction as a member of this material class of ferromagnetic shape memory alloys for the first time. Thereby monocrystals with the nominal chemical composition Co 38 Ni 33 Al 29 were initially studied in the austenitic phase, in order to contribute to a better understanding of the complex behaviour of this material by means of a further diffraction method with a high informational content. While in the present two phase structure the precipitates could be clearly identified and confirmed as face-centred cubic cobalt solid solution by the Kossel diffraction, whereas for the expected B2-structure only 2 of the needed 5 superstructure reflections could be proved by means of the Kossel technique. A possible explanation lies besides the reason of a weak reflection intensity in a very strong discrepancy of 21 % of the ideal stoichiometric composition of (Co, Ni) 50 Al 50 in the investigated (Co, Ni) 71 Al 29 . As known from the literature to maintain the B2-structure under such conditions is only possible by the formation of an enormous number of so-called constitutional crystal defects, which could be used to explain the non-verified superstructure reflections. Moreover, the local lattice constant of the main crystal phase β was determined to a = (0.2855 ± 0,0002) nm by the Kossel technique.