Effect of ternary additions to structural properties of NiTi alloys

Abstract

In this work, the effects of small ternary additions to B2 NiTi structures was investigated through DFT calculations. The analysis considered deviations from stoichiometry arising from either simple substitution of host atoms in a given sublattice or from the formation of anti-sites. The calculations enabled the determination of the site preference of X ternary additions. Moreover, the results suggest that ternary additions located in the central region of the transition metal group across all periods tend to occupy Ni sites due to favorable X-Ti nearest neighbor (NN) interactions. This occupancy is achieved through substitution or through the generation of anti-site defects. On the other hand, ternary additions at both ends of a given transition metal row tend to occupy Ti sites due to favorable X-Ni NN interactions. Once site preferences are determined, the effect of alloying on the thermodynamic and mechanical properties of B2 NiTi-X structures are presented and trends are discussed.

<i>Ab Initio</i> Prediction of Atomic Location of Third Elements in B2-Type TiNi

“…Finally, we discuss our results above on the third elements site preferences in B2 type Ti-Ni-X (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) comparing to other prior approaches based on rst-principle calculations by Sheng et al 16) and Singh et al 22) To our knowledge, the earliest work on the current issue above approached by the electronic structure calculation was made by Sheng et al 16) They predicted the substitution behavior of third elements in TiNi compounds by the calculation using the DV-Xα cluster method, in which bond orders between X and Ti (Ni) were estimated employing Mulliken population analysis. As for the site preference trend of 3d transition metal elements in the B2-type Ti 8 Ni 6 X or Ti 6 Ni 8 X cluster consists of 15 atoms (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu), their results all agree with those of ALCHEMI analysis by Nakata et al 5,6) It overall coincides with our results using VASP, except for Cr and Mn as mentioned in the previous section.…”

“…In the most recent work at this moment using VASP on the third elements site preferences in TiNi compounds, Singh and collaborators 22) have reached their conclusions as follows: (1) Sc substitutes Ti site, and (2) Cr, Mn, Fe, Co, and Cu substitute Ni site, respectively, in either super lattice model of Ti-or Ni-rich. (3) V substitutes de cient site of Ti or Ni.…”

“…Singh et al 22) used Vienna Ab initio Simulation Package (VASP) to predict the site preference of third elements in the B2-type TiNi. They employed super lattice models of Ni 15 7,8) However, Cr, Mn, Cu and Pd disagree with those.…”

Computational Thermodynamics and Kinetics-Based ICME Framework for High-Temperature Shape Memory Alloys

“…Such calculations are important given the susceptibility of NiTi-based SMAs to hydrogen embrittlement [98]. Very recently, the present authors and collaborators [99] have used DFT methods to predict the site preference for different ternary additions to NiTi-based SMAs as shown in Fig. 10.…”

In Situ Neutron Diffraction Study of NiTi–21Pt High-Temperature Shape Memory Alloys

“…Increasing the application temperature of shape memory alloys (SMAs) is one of the main objectives in the development of solid-state actuators for aerospace, automotive, and other industrial applications. Over the years, numerous NiTi-based alloys have been investigated with macro-additions of Zr, Hf, Pd, Pt, and Au, and have been shown to exhibit transformation temperatures in excess of 500°C [1][2][3]. In particular, Pt proved to be an effective alloying addition, raising the martensitic transformation temperature as much or more substantially than any other ternary additions [1,4].…”