Local atomic and crystal structure rearrangement during the martensitic transformation in Ti50Ni25Cu25 shape memory alloy

The changes of crystal structure and local crystalline environment of Ti, Ni and Cu atoms in Ti50Ni25Cu25 shape memory alloy are investigated using X-ray diffraction and extended X-ray absorption fine structure spectroscopy (EXAFS) in temperature range of martensite transformation. The analysis of the EXAFS-spectra shows that the bonds involving Ni atoms have the highest degree of disorder and the change in the local environment around Ni atoms is significant for the occurrence of the shape memory effect, while Cu atoms occupy the normal positions in the crystallographic structure and have the lowest displacement amplitude leading to the stabilization of both phases.