Abstract
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 (ΔE) 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 ΔE increases sharply with Pt concentration. It was found that the phase transition temperatures are closely related to the energy differences ΔE between parent and martensite phases. The electronic structures of martensite B19 and B19′ phases are also discussed.
Highlights
NiTi shape memory alloys (SMAs) exhibit the shape memory effect and superelasticity which are attributed to reversible thermoelastic martensitic transformations (MTs)
We describe the martensitic transformation through the energy differences between austenite and martensite phases in TiNiPt alloys
In the present paper we explored the strong dependence of the martensite start temperature martensite start temperatures (Ms) on alloy composition in ternary Ni-Ti-Pt shape memory alloys by means of density functional theory
Summary
NiTi shape memory alloys (SMAs) exhibit the shape memory effect and superelasticity which are attributed to reversible thermoelastic martensitic transformations (MTs). There are many reports on the crystal structures [11,14,15,16,17], phase transformations [18,19,20,21,22,23,24], shape-memory behaviors [12,25,26,27,28,29], and precipitate phases [30,31,32,33,34] in NiTiX (X = Pd, Hf, and Zr) alloys Of these HTSMAs, the (Ni,Pt)Ti system, owing to the highest potential use temperature, in spite of the high costs, has been studied as the promising SMAs for demanding applications, such as in the aerospace, automotive, power generation, and chemical processing industries. The MTs of ternary TiNiPt HTSMAs as a function of the Pt content is investigated in the present research by first principles
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