Abstract:Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, the binding energy ΔE and the electronic structure of the NiTiNb shape memory alloy doped with Co, Pd elements have been systematically calculated and analyzed carefully. The results show that the ΔE and ΔH of NiTi(Co→Ni) and NiTi(Nb, Co→Ni) models are smaller than those of NiTi(Co→Ti) and NiTi(Nb, Co→Ti), which means the alloying element Co will replace Ni atom in NiTiNb alloy. However, the Mulliken population and electronic density calculations show that the Co will cohere the nearest neighbor Ti atoms to be confined by strong bonds after solid solution, resulting in the Ni/Ti ratio increasing instead of decreasing by Co→Ni reaction process, then the Ms of NiTiNb(Co) is decreased. To Pd element addition, although the ΔH of NiTi(Pd→Ti) and NiTi(Nb, Pd→Ti) crystals are bit smaller than that of NiTi(Pd→Ni) and NiTi(Nb, Pd→Ni), the ΔE of the Pd replacing Ni models are much smaller than those of Pd replacing Ti. And the Mulliken population results show that some strong metallic bonds appear between Pd and Ti atoms in Pd→Ni solid solution reaction. So the Ms of NiTiNb(Pd) alloy will increase by the addition of Ni/Ti ratio for Pd taking the place of Ni. Then it can be seen, the bond strength between alloying elements and Ni or Ti atoms is the other micro-factor influencing on the ratio of Ni/Ti to the Ms.