Ab Initio Study of Martensitic Transformation in NiTiPt High Temperature Shape Memory Alloys

The crystal structures and martensitic transformation of Ti50Ni50-xPtx alloys (x = 0, 6.25, 8.33, 10.42, 12.5, 18.75, 25) were studied by means of density functional theory (DFT). The computational results indicate that the lattice parameters of Ti-Ni-Pt alloys continuously increase with increasing the Pt content. It is found that at <= 12.5 at.% Pt, the martensite structure is monoclinic B19 ' phase, and the energy differences between parent and martensite phases (Delta E) decrease slightly with a minimum observed at 6.25 at.% Pt. However, when the Pt content is increased to around 15 at.%, the most stable martensite phase is the orthorhombic B19 structure, and the Delta E increases sharply with Pt concentration. It was found that the phase transition temperatures are closely related to the energy differences Delta E between parent and martensite phases. The electronic structures of martensite B19 and B19 ' phases are also discussed.

Automated summary

The study found that the lattice parameters of Ti-Ni-Pt alloys continuously increase with increasing Pt content. Below 12.5% Pt, the most stable martensite structure is monoclinic B19' phase with the minimum energy difference observed at 6.25% Pt, while around 15% Pt, the orthorhombic B19 structure becomes the most stable martensite phase with a sharp increase in energy difference.