First principle study on NiTi alloyed with transition elements

Lattice parameters, formation energy, elastic modulus and deformation charge density of NiTi alloyed by 3d, 4d, 5d transition elements have been calculated by the first principle method based on density functional theory (DFT). Then we discussed the site preference of transition elements in NiTi and their influence on the martensitic transformation temperature of NiTi. The results show that when the transition elements are added to NiTi alloy: (1) the groups of V, Cr, Mn, Fe, Co, Pd, Cu prefer the Ni-sites; (2) Sc, Y, Zr, Hf prefer the Ti-sites; (3) Zn and Cd can't form a stable structure. In the martensitic phase transformation process, the bigger C44 /C' and stronger bonding interaction mean the stronger transition resistance, which lead to a lower transformation temperature. By analyzing the elastics modulus and the differential charge density map of NiTi, we can infer that: (1) the replacement of Ni by the groups of V, Cr, Mn, Fe, Co or by Pd, Pt and the replacement of Ti by V, Cr, Mn, Fe will lower the transformation temperature M_s; (2) substitution of Hf, Zr, Ag, Au for Ni and substitution of Sc, Y, Hf, Zr for Ti will increase the transformation temperature M_s; (3) transformation temperature will be almost unchanged when Cu substitutes for Ni. These results are consistent with the experimental and we can understand the influence of alloying elements on the phase transformation temperature of NiTi from the microscopic point of view.